Supraglottic airways in difficult airway management: successes, failures, use and misuse
- Consultant Anaesthetist, Department of Anaesthesia and Pain therapy, Helios Klinikum Emil von Behring, Berlin, and Privatdozent (Associate Professor) of Anaesthesia, Intensive Care and Emergency Medicine, Georg-August University of Goettingen, Goettingen, Germany
Priv. Doz. Dr med. A. Timmermann
Supraglottic airway devices (SAD) play an important role in the management of patients with difficult airways. Unlike other alternatives to standard tracheal intubation, e.g. videolaryngoscopy or intubation stylets, they enable ventilation even in patients with difficult facemask ventilation and simultaneous use as a conduit for tracheal intubation. Insertion is usually atraumatic, their use is familiar from elective anaesthesia, and compared with tracheal intubation is easier to learn for users with limited experienced in airway management. Use of SADs during difficult airway management is widely recommended in many guidelines for the operating room and in the pre-hospital setting. Despite numerous studies comparing different SADs in manikins, there are few randomised controlled trials comparing different SADs in patients with difficult airways. Therefore, most safety data come from extended use rather than high quality evidence and claims of efficacy and particularly safety must be interpreted cautiously.
Definitions and devices
Most supraglottic airway devices (SADs) are designed for use during routine anaesthesia, but there are other roles such as airway rescue after failed tracheal intubation, use as a conduit to facilitate tracheal intubation and use by primary responders at cardiac arrest or other out-of-hospital emergencies . Supraglottic airway devices are intrinsically more invasive than use of a facemask for anaesthesia, but less invasive than tracheal intubation.
The term ‘extraglottic airway device’ may be more accurate than ‘supraglottic’, since it includes all devices that lie inside the oropharyngeal and oesophageal area, but outside the glottis. Figure 1 illustrates how depth of airway instrumentation correlates with anatomical position . However, the term ‘extraglottic’ is not in common use in the English literature, so the term ‘SAD’ is used here to include all extraglottic devices.
Supraglottic airway devices can usefully be classified as first and second generation SADs and also according to whether they are specifically designed to facilitate tracheal intubation. First generation devices are simply ‘airway tubes’, whereas second generation devices incorporate specific design features to improve safety by protecting against regurgitation and aspiration . The first generation SADs include the classic LMA™ (cLMA, Intavent Direct, Maidenhead, UK) and all other standard laryngeal mask airways (LMAs). This group also includes the CobraPLA™ perilaryngeal airway and CobraPLUS™ Airway (Pulmodyne, Indianapolis, IN, USA) although their design differs substantially from the cLMA.
The second generation SADs include the LMA Pro-Seal™ (PLMA), the LMA Supreme™ (SLMA) (both Intavent Direct) and the i-gel™ (Intersurgical, Wokingham, UK). These devices all incorporate a drain tube to separate the respiratory and gastrointestinal tracts and minimise the risk of aspiration. They also create a higher oropharyngeal leak pressure compared with the first generation SADs [4–8]. The SLIPA™ Airway (Streamlined Liner of the Pharynx Airway, SLIPA, CurveAir Limited, London, UK) has design features (a sump) that arguably makes it a second generation device but there is little evidence of performance benefit.
Some SADs are specifically designed to enable or assist in tracheal intubation, e.g. the LMA Fastrach™ (Intubating LMA, ILMA, available in reusable and single use versions, Intavent Direct) and the Air-Q™ Laryngeal Airway Device (also reusable and single use versions, Mercury Medical, Clearwater, FL, USA). Tracheal intubation may also be possible via other SADs not specifically designed for this role, while others are poorly suited to this role. In broad terms, standard LMAs, the i-gel and PLMA perform well while the Laryngeal Tubes and SLMA are less well suited to such use due to narrow calibre airway tubes (SLMA) or airway orifices (Laryngeal Tube family).
Finally, oesophageal blockers were initially designed for emergency airway management, e.g. in an out-of-hospital setting and for usage by medical personnel who do not perform tracheal intubation on a daily basis. They consist of two blocking cuffs, one in the laryngopharyngeal area (marked B in Fig. 1) and the other in the oesophageus (marked D in Fig. 1). Ventilation is provided through an outlet between the two cuffs. The Combitube™ (Tyco Healthcare-Kendall, Pleasanton, California), Easytube™ (Ruesch, Kernen, Germany) and different versions of the Laryngeal Tube (original Laryngeal Tube), disposable version (LT-D) Laryngeal Tube suction mark II (LTS II) and disposable version (LTS D), all VBM, Sulz, Germany) all belong to this group. Amongst the Laryngeal Tubes those without a drain (LT and LT-D) can be considered first generation SADs and those with a drain tube as second generation devices (LTS II and LTS-D).
According to Brimacombe  there are five major considerations that highlight the role of a LMA in the management of the difficult airway: first and foremost, the anatomical and/or technical factors making facemask ventilation and laryngoscope-guided tracheal intubation difficult do not usually influence LMA insertion and function. Thus, in situations where facemask ventilation and laryngoscope-guided tracheal intubation have failed, the LMA has a high likelihood of succeeding. Secondly, the LMA can be used both as a ventilatory device and for intubation of the airway. Thirdly, tracheal intubation via the LMA can take place in an unhurried fashion while the patient is being oxygenated and his/her lungs ventilated. Fourthly, insertion of the LMA is atraumatic and does not reduce the chances of other techniques subsequently succeeding. Finally, the widespread use of the LMA in routine anaesthesia practice means that it is readily available and most anaesthesiologists reasonably skilled in its use.
Therefore, the use of the LMA is now included in many difficult airway guidelines. The American Society of Anesthesiologists includes the LMA as a ventilatory device at two points in the algorithm: first in the anaesthetised patient whose trachea cannot be intubated (anaesthetised non-emergency limb); and second in the anaesthetised patient whose trachea cannot be intubated and whose lungs cannot be conventionally ventilated (anaesthetised emergency limb) . A similar strategy is described in the algorithm of the Difficult Airway Society in the UK . This algorithm recommends the use of a cLMA: (i) during an unanticipated difficult tracheal intubation as a conduit for fibreoptic-guided tracheal intubation (with the ILMA as an alternative); (ii) during failed intubation in the setting of rapid sequence induction as a method of airway rescue (with the PLMA as an alternative); and (iii) as a rescue device in the event of a ‘cannot intubate cannot ventilate’ situation. Comparable uses can also be found in many other national recommendations such as those from Germany or Italy [12, 13]. In addition, Weiss and Engelhard recently published a proposal for management of the difficult paediatric airway . In the situation of failed facemask ventilation and failed tracheal intubation, they recommended the use of the LMA or ILMA first for ventilation and also as a conduit for tracheal intubation. The LMA is likely to be equally prominent in the paediatric difficult airway guidelines currently under development by the Association of Paediatric Anaesthetists of Great Britain and Ireland and the Difficult Airway Society, and is also included as the Plan B after failed tracheal intubation in the recommendations of the working group on Paediatric Anaesthesia of the German Society of Anaesthesia and Intensive Care Medicine .
Therefore, the LMA and in particular the ILMA has become an integral part of each algorithm, especially in management of the unanticipated difficult airway. Of note, since the development of these guidelines, many of which are more than a few years old, numerous newer SADs have been designed and several have been shown to have performance benefits over the cLMA in some circumstances (e.g. improved airway seal, more reliable ventilation, easier use as a conduit, access to the gastrointestinal tract, improved protection against aspiration). It is therefore arguable that several SADs other than the standard LMA and ILMA should be included in updated difficult airway algorithms.
Manikin vs patient-based studies
Rai and Popat recently commented on the large number of manikin studies in airway management research and the relative lack of similar studies in patients . They posed the question as to what should be the minimum evidence to label an airway device as efficacious and fit for purpose.
They refer to an editorial by Cook, who suggested that a new airway device should undergo a three-stage process . In stage 1, devices are evaluated on the bench-top and in specifically designed manikins; in stage 2, a rigorous pilot study takes place to determine whether the device is effective and safe; and in stage 3, the device is compared in a randomised controlled trial (RCT) against the current gold standard for the procedure for which it is expected to be used (e.g. in the case of first generation SADs, the cLMA).
The problem nowadays is that most studies only focus on stage 1, the manikin-based study, but do not progress to stages 2 or 3, which will require study of patients. There are several reasons for this. Many ethics committees do not consider approval necessary for manikin studies and if approval is applied for, it is usually easily obtained and participant information, consent and recruitment involve staff and not patients . Furthermore, there are no adverse effects that might potentially halt the trial. The study can be completed in days, for example in a training course, rather than months or years.
But the patients’ anatomy and physiology differ in many respects, which cannot be modelled by simple manikins or even sophisticated simulators . Manikins do not represent easy or difficult human anatomy in its enormous variety (for example the lack of obese manikins is a notable omission). The manikin’s upper airway ‘tissues’ are stiff, non-compliant, static and generally patent rather than soft, fragile, dynamic and collapsible as in humans. Secretions, lubrication and bleeding are simulated poorly (if at all); there are no coughing reflexes, or modelling of regurgitation or aspiration, that may impair ventilation or the view to the larynx. Difficulties in standard procedures such as mask ventilation or tracheal intubation are mostly reflected unrealistically and the fidelity of SAD insertion is also very poor .
Even when there are reasons why a manikin-based study is appropriate (e.g. the study design requires conditions that cannot be recreated in patients), there is a trend to extrapolate data from stage 1 to clinical practice. While it is extremely frequent to read in researchers’ concluding statements that ‘further clinical studies are needed to evaluate the effectiveness of the device in patients’, these studies are rarely done. One of the exceptions is a trial from our own group, where the study design was first applied to manikins  and in a follow up a RCT (level 1b) performed on patients in the operating room . There are other examples where both stages are performed in the same study [23, 24].
Therefore, in accordance with Rai and Popat’s conclusion that “in very much the same way as the trainee graduates from a manikin to a patient when using a new airway device, it is time for serious researchers to move on to study patients rather than manikins”, the following articles will - whenever possible and not otherwise noted - reflect data obtained in human rather than manikin studies.
Level of evidence
More recently, Pandit et al. described a very reasonable strategy for airway equipment evaluation, based on the recommendation of the ‘Airway Device Evaluation Project Team’ of the Difficult Airway Society . They refer to evidence-based hierarchies from level 1a to 5 (Table 1) and while acknowledging that there are other useful ways to judge research evidence, they propose that local purchasers might demand a minimum level of published evidence on a new airway device before considering it for purchasing.
|1a||Systematic review of RCTs|
|1c||All-or-none study (i.e. when all patients died before the therapy became available, but some now survive on it; or when some patients died before the therapy became available, but none now die on it)|
|2a||Systematic review of Level 2b cohort studies|
|2b||Single cohort study or low-quality RCT|
|2c||Outcomes studies that investigate outcomes of healthcare practices using epidemiology to link outcomes (e.g. quality of care, quality of life) with independent variables such as geography, income or lifestyle, etc.|
|3a||Systematic review of Level 3b studies|
|3b||Single case-control or historical-control study|
|4||Case report or case series|
|5||Expert opinion or ideas based on theory, on bench studies or first principles alone|
Level 3b is judged the minimum level of evidence that can be subjected to a systematic review, in turn helping create level 3a evidence that can be assimilated into a wider evidence base. The authors acknowledge that level 2 and higher levels are of course acceptable (even desirable) and that results of RCTs will be useful, but for pragmatic reasons they try to define a minimum level of evidence to balance between what is achievable and what is meaningful. They illustrated this balance as level 5 being easily achievable but barely meaningful, whereas level 1 RCTs are very meaningful but difficult to achieve. For these reasons, level 3b is judged to be an appropriate point of balance as an adequate minimum level of evidence, that should be required before a purchaser might consider a device, although this evidence is not itself a sufficient criterion for equipment selection. While this argument is largely applied by Pandit et al. to purchase of devices for elective use, logically it is equally if not more important to apply it to devices for difficult airway management and emergency use.
Ventilation via different SADs in a difficult to manage airway
Since the development of the cLMA more than 20 years ago, there is now a much increased choice of SADs. For many SADs, however, there is still a lack of high-quality data regarding efficacy . To fulfil the requirements of Cook’s stage 3, and the best evidence, RCTs comparing each new device against an established alternative are needed. These studies need to be suitably powered to detect clinically relevant differences in outcomes. Given the lack of such studies in elective anaesthetic use, it is not surprising that there are even fewer such studies in the setting of difficult-to-manage airways. Not only are ‘true’ difficult airways rare but, as this situation is potentially dangerous for the patient, best clinical practice is needed to resolve the airway challenges.
There is a considerable body of data (level 3b and 4) about the successful use of the ‘gold standard’ cLMA in patients with difficult to manage airways: over 300 publications including more than 3000 such patients . Also the ILMA, designed especially for the management of the difficult airway, has been described as being successfully used for ventilation in the anticipated [26–32] and unanticipated [33, 34] difficult airway in 97–100% of cases.
Case reports or series (level 4) of successful ventilation in patients with difficult airways have been described for many other SADs: the LMA PLMA [35–41], the SLMA [42–44], the i-gel [45–50], the Ambu-i™, the Air-Q [52–55], the CobraPLA  and the CobraPLUS . The Laryngeal Tube, designed for emergency ventilation, is also successfully described in difficult airway management in elective adult  and paediatric  patients in the operation room. Up until now there are no publications published in a peer reviewed journal about the use of the SLIPA in patients with difficult airways.
The so-called second generation SADs offer some important benefits over the first generation SADs: (i) they provide a higher leak pressure, which makes ventilation with higher airway pressure possible; (ii) they offer feedback of correct pharyngo-laryngeal positioning with the tip in the post-cricoid region (PLMA and SLMA), which potentially reduces the chance of gastric insufflation; and (iii) access via the drain tube facilitates the insertion of a gastric tube for drainage of the stomach and potentially reduces the risk of regurgitation and aspiration . Although these benefits are important in elective surgery, there are no clinical trials demonstrating benefit or higher success rates in difficult airways.
There are only a few RCTs comparing other SADs against the cLMA in patients with a difficult airway. In 1998, Langenstein and Moeller reported the success rates for ventilation via the cLMA and the ILMA in patients whose tracheas were difficult to intubate: efficacy was similar with 92% vs 93% success, respectively . Two recently published RCTs, examining intubation through different SADs in patients with predictors of difficult intubation, did not find any significant difference in rates of successful ventilation between the single-use ILMA and the i-gel (78/80 vs 79/80, respectively) [61, 62].
In conclusion, there are reports of successful ventilation in patients with difficult airways, for many of the newer SADs, but there are not enough data to judge any individual device as superior. While several of the newer devices have design features that might be expected to improve ease of insertion or efficacy of subsequent ventilation, the cLMA remains the device with the greatest body of published literature. For many single-use LMAs there are no such published data at all. To some extent, therefore, the decision on which SAD to use to establish ventilation when airway management proves difficult is likely to be based on extrapolation from data in trials of patients undergoing elective anaesthesia whose airways are known not to be difficult to manage.
Intubation through a SAD
Intubation through a SAD has been reported using a blind technique and assisted by lightwands, optical stylets or flexible fibreoptic guidance. Flexible fibreoptic guided intubation through a SAD is facilitated by use of an Aintree™ intubation catheter (AIC; Cook Ireland Ltd., Limerick, Ireland, Fig. 2) [63–65] or a guide wire . In some SADs these techniques are compulsory as the airway lumen or outlet is too small to advance a tracheal tube of appropriate size: this is so for the SLMA, Laryngeal Tube and Combitube.
The ‘gold standard’ for blind intubation is the reusable ILMA, which is only available for patients over 30 kg. In a meta-analysis in 2005, Brimacombe reported a 90% overall blind success rate in 2221 patients with normal airways in 23 non-RCTs (level 3a and 4) and a 90% success rate in 618 patients with abnormal airways in 16 non-RCT studies . The success rate in patients with abnormal airways may increase to 100%, if a flexible Lightwand™ (Vital signs, Totowa, NJ, USA) [33, 68], a Trachlight™ (Teleflex Medical Europe Ltd, Athlone, Ireland) , a Foley optical stylet tool™ (Clarus Medical, Minneapolis, MN, USA)  or a flexible fibrescope [26, 28] is used.
Blind intubation via many SADs fails either because of non-alignment of the device orifice and the glottis or, more frequently, because a tube or introducer passed down the SAD exits the ventilation orifice posteriorly and enters the oesophagus. Most SADs therefore, with the exception of those specifically designed for intubation, require fibreoptic guidance to increase the rate of successful intubation, even in patients with normal airways, above around 15%.
Successful fibreoptic guided intubation of a difficult airway via many other SADs has been reported: via the cLMA in adults [71, 72] and children [73, 74] and the PLMA in grossly and morbidly obese patients . Case reports have been published with the SLMA , Aura-i™ (Ambu)  and i-gel . There is a report of successful fibreoptic guided intubation via the i-gel in two patients in whom the technique failed via a cLMA .
Just recently, a few level 1b studies (RCTs) have been published comparing different SADs with the ILMA. Results for blind intubation are reported in Table 2. There is one study comparing fibreoptic guided intubation through the single use ILMA and the i-gel in patients with predictors of a difficult airway . Only one attempt was allowed for intubation and reported success rate was not statistically significantly different: ILMA (90%); i-gel (96%). Of note for blind intubation, the single-use ILMA was considerably more successful than the i-gel: 69% vs 15%, respectively.
|Theiler et al., 2011 *||80||Yes||69%||15%|
|Karim and Swanson, 2011 †||154||No||99%||77%|
|Erlacher et al., 2011 ‡||180||No||95%||57%||47%|
|Darlong et al., 2011 §||60||No||90%||87%|
In summary, for blind intubation via a SAD the largest number of published studies and the greatest clinical experience is for the reusable ILMA. Again, there are reports of successful fibreoptic guided intubation via many newer SADs but there are not enough data to judge any of them to be superior over the ‘gold-standard’ ILMA.
The use of SADs for difficult airway management in the pre-hospital setting
The importance and prevalence of SADs in airway management in the pre-hospital setting have increased considerably in recent years. There are three main reasons for this: (1) emergency tracheal intubation outside the hospital environment is notably more likely to fail than during elective anaesthesia in hospital; (2) equipment and strategies to manage the difficult airway are limited outside hospital; and (3) direct laryngoscopy is frequently performed by paramedics or emergency medicine physicians who do not practice tracheal intubation on a daily basis .
In contrast to the controlled environment of the operating theatre, out-of-hospital airway management often involves coping with the presence of debris, secretions, blood, vomitus, anatomical derangement, dental damage, or the application of cervical spine immobilisation devices or in-line axial stabilisation. Together, these factors reduce the success rates of direct and indirect laryngoscopy techniques and facemask ventilation. Respiratory dysfunction and hypoxia are also often present and the position of the patient sometimes makes access to the head difficult. Other issues complicating airway management of the emergency pre-hospital patient include simultaneous performance of cardiopulmonary resuscitation (CPR) or other medical procedures, altered and varying levels of patient consciousness and lack of trained assistance . As a result, the incidence of difficult laryngoscopy reported by experienced anaesthesiologists during emergency laryngoscopy may be as high as 20% in adult  and paediatric  patients, much higher than in the operating room .
According to studies by Konrad et al.  and Mulcaster et al.  laryngoscopic-guided tracheal intubation must be performed approximately 50–60 times in patients who appear to be normal on routine airway examination to achieve proficiency. Johnston et al.  reported an average of only 6–10 tracheal intubations performed by paramedics during their airway management training in the operation room. Therefore, success rates as low as 50% have been noted for emergency medical technicians, who do not perform tracheal intubation frequently, even under the controlled environment of the operating room . A survey among German pre-hospital emergency physicians (non-anaesthesia trained), however, also demonstrated that 20% of the physicians had performed fewer than 20 tracheal intubations under supervision before their assignment to the rescue service .
Therefore, several studies report the incidence of a surgical airway to be as high as 10–15% when direct laryngoscopy was attempted by paramedics [74, 75]. A high incidence of unrecognised misplaced tubes following intubation by paramedics has also been reported: when the position of tracheal tubes placed out-of-hospital was re-examined by independent observers on arrival in the emergency department, unrecognised oesophageal or hypopharyngeal intubation was recorded in up to 25% [76, 77]. One study also reported an incidence of unrecognised oesophageal intubations of 6.7% when tracheal intubation was performed by emergency medical service physicians . While the 24-h mortality rate of patients whose tracheas were intubated correctly was reported as 10%, this rate increased dramatically to 70–90% for those with misplaced tubes [77–79].
With these high rates of failure of airway management, it can therefore justifiably be argued that in the pre-hospital setting all airways are, at least potentially, difficult airways. Use of SADs in the pre-hospital setting should be judged in this context.
It is therefore understandable that despite the fact that tracheal intubation is perceived as the optimal method of providing and maintaining a clear and secure airway, the 2010 European Resuscitation Guidelines recommend that tracheal intubation is only attempted when trained personnel are available to carry out the procedure with a high level of skill and confidence . Several SADs are now included in these recommendations and in guidelines for out-of-hospital airway management, not only for management of difficult intubation but as a primary approach for those who do not perform tracheal intubation regularly [85–87].
The particular benefits of use of an appropriate SAD over facemask ventilation in the pre-hospital setting include higher success rate and tidal volume, less hand fatigue  and less gastric insufflation, regurgitation or aspiration (during continuous chest compression) . Ventilation with an automated ventilator is possible, which frees the rescuer for other tasks . Compared with tracheal intubation, SADs have a higher success rate and are quicker to insert [22, 91] and unlike tracheal intubation, they can generally be inserted without interrupting chest compressions (at least in manikins) . The unique problems of pre-hospital care (e.g. lack of starvation, necessity for assisted ventilation perhaps during chest compressions) mean that second generation SADs logically have more desirable performance features than first generation devices.
Several SADs have been considered for pre-hospital airway management. There are published studies in patients undergoing CPR or during trauma management with the cLMA [93–96], the SLMA [44, 97], the ILMA [98–103], the i-gel , the Combitube [95, 96, 105–107] and versions of the Laryngeal Tube [108, 109]. None of these studies have been adequately powered to enable survival to be studied as a primary endpoint; instead, most researchers have studied insertion and ventilation success rates. There are no RCTs comparing different SADs (even in terms of successful ventilation and insertion times) in the pre-hospital setting. Such studies are needed to inform this evolving area of practice.
Of note, data obtained in the controlled environment of the operating room or in simulated manikin scenarios cannot automatically be transferred to the pre-hospital setting. An example of this is a recent study by Trimmel  comparing out-of-hospital intubation success rates of a conventional laryngoscope with those of the Airtraq® videolaryngoscope (King Systems, Noblesville, IN, USA) in the pre-hospital setting. Although the Airtraq has been demonstrated to be effective in elective patients in the operating theatre [111–114], in the pre-hospital setting anaesthesia trained emergency physicians achieved only 49% successful tracheal intubation with the Airtraq, whereas conventional laryngoscopy was successful in 99%. Moreover, in 54 of 56 patients where Airtraq intubation failed, direct laryngoscopy was successful on the first attempt.
Hence, there is not enough evidence to support the routine use of any specific SAD in pre-hospital airway management. The best technique is dependent on the precise circumstances and the competence of the rescuer achieved by training in patients under supervision in a controlled environment .
Several factors support the use of a SAD in the management of the difficult airway. Many studies and case reports or series have been published that illustrate the efficiency of SADs in difficult ventilation and failed intubation situations. Supraglottic airway devices are included in many guidelines and recommendations for securing the airway in diverse medical environments. By far the most publications and clinical experience still exist for the cLMA and ILMA. Numerous studies compare different SADs in huge variety of ‘clinical settings’ in manikins, but there are very few comparable studies in appropriate patients. The results of manikin studies cannot be assumed to transfer to clinical practice due to the low fidelity of manikins’ upper airways both in terms of anatomy and physiology. At present there is inadequate robust evidence to support any of the new SADs as superior to the so called ‘gold standards’. To determine whether any of the newer SADs (with design features that might be anticipated to offer performance benefits) offer genuine clinical advantages, properly powered RCTs in patients with difficult-to-manage airways are needed, both in hospital and in the pre-hospital setting.
No external funding or competing interests declared.
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© 2011 The Author. Anaesthesia © 2011 The Association of Anaesthetists of Great Britain and Ireland
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- Accepted: 10 Sept 2011
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The difficult airway with recommendations for management – Part 1 – Difficult tracheal intubation encountered in an unconscious/induced patient
Prise en charge des voies aériennes – 1re partie – Recommandations lorsque des difficultés sont constatées chez le patient inconscient/anesthésié
Department of Anesthesia, Queen Elizabeth II Health Sciences Centre, Dalhousie University, Halifax Infirmary Site, 1796 Summer Street, Halifax, NS B3H 3A7 Canada
J. Adam Law, Phone: +902-473-4326, Fax: +902-473-3820, Email: ac.lad@walj.
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Received 2013 Feb 28; Accepted 2013 Aug 13.
Copyright © The Author(s) 2013
Open AccessThis article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited.
This article has been cited by other articles in PMC.
Previously active in the mid-1990s, the Canadian Airway Focus Group (CAFG) studied the unanticipated difficult airway and made recommendations on management in a 1998 publication. The CAFG has since reconvened to examine more recent scientific literature on airway management. The Focus Group’s mandate for this article was to arrive at updated practice recommendations for management of the unconscious/induced patient in whom difficult or failed tracheal intubation is encountered.
Nineteen clinicians with backgrounds in anesthesia, emergency medicine, and intensive care joined this iteration of the CAFG. Each member was assigned topics and conducted reviews of Medline, EMBASE, and Cochrane databases. Results were presented and discussed during multiple teleconferences and two face-to-face meetings. When appropriate, evidence- or consensus-based recommendations were made together with assigned levels of evidence modelled after previously published criteria.
The clinician must be aware of the potential for harm to the patient that can occur with multiple attempts at tracheal intubation. This likelihood can be minimized by moving early from an unsuccessful primary intubation technique to an alternative “Plan B” technique if oxygenation by face mask or ventilation using a supraglottic device is non-problematic. Irrespective of the technique(s) used, failure to achieve successful tracheal intubation in a maximum of three attempts defines failed tracheal intubation and signals the need to engage an exit strategy. Failure to oxygenate by face mask or supraglottic device ventilation occurring in conjunction with failed tracheal intubation defines a failed oxygenation, “cannot intubate, cannot oxygenate” situation. Cricothyrotomy must then be undertaken without delay, although if not already tried, an expedited and concurrent attempt can be made to place a supraglottic device.
Actif au milieu des années 1990, le Canadian Airway Focus Group (CAFG), un groupe dédié à l’étude des difficultés imprévues dans la prise en charge des voies aériennes, a émis des recommandations sur ce sujet dans une publication datant de 1998. Le CAFG s’est réuni à nouveau pour passer en revue la littérature scientifique récente concernant la prise en charge des voies aériennes. Dans cet article, le CAFG s’est donné pour mission d’émettre des recommandations visant la prise en charge du patient inconscient ou anesthésié qui présente des difficultés d’intubation significatives.
Dix-neuf cliniciens ayant une formation en anesthésie, en médecine d’urgence ou en soins intensifs composent le CAFG actuel. Les participants ont passé en revue des sujets précis en consultant les bases de données Medline, EMBASE et Cochrane. Les résultats de ces revues ont été présentés et discutés dans le cadre de téléconférences et de deux réunions en personne. Lorsqu’indiqué, des recommandations fondées sur des données probantes ou sur un consensus ont été émises. Le niveau de confiance attribué à ces recommandations a aussi été défini.
Le clinicien doit avoir conscience des lésions qu’il peut infliger lors de tentatives multiples d’intubation trachéale. Il est possible d’éviter de telles lésions en abandonnant rapidement une technique d’intubation infructueuse afin d’opter pour une méthode alternative (ou ‘plan B’) à condition que l’oxygénation par masque facial ou par l’utilisation d’un dispositif supraglottique s’avère possible. Nonobstant la ou les techniques choisies, un maximum de trois tentatives infructueuses mène à la conclusion qu’il s’agit d’un échec d’intubation et devrait inciter le clinicien à adopter une stratégie de retrait. Une situation dans laquelle il est impossible de procéder à l’oxygénation du patient à l’aide d’un masque facial, d’un dispositif supraglottique ou de l’intubation endotrachéale est qualifiée de scénario cannot intubate, cannot ventilate. Il est alors impératif de procéder sans délai à une cricothyrotomie, à moins que l’insertion d’un dispositif supraglottique n’ait été tentée. Celle-ci peut alors être effectuée rapidement et parallèlement à la réalisation de la cricothyrotomie.
What other statements of recommendation are available on this topic?
In 1998, Canadian recommendations were published on management of the unanticipated difficult airway. More recent national recommendations and guidelines on difficult airway management have been published in the USA, the United Kingdom, and other western European countries.
Why were these recommendations developed?
Canadian recommendations were overdue for an update. Since the last review, many new devices useful in difficult airway management have been introduced. In addition, the Anesthesia Closed Claims Project and other observational studies have highlighted potential areas for improvement in management of the difficult and failed airway.
How do these statements differ from existing recommendations?
These statements reflect current evidence and thinking on an appropriate response to difficult airway management encountered in the unconscious/induced patient. The importance of engaging an exit strategy after a limited number of attempts at tracheal intubation is emphasized, as is a simplified response to a failed oxygenation, “cannot intubate, cannot oxygenate” situation.
Why do these statements differ from existing recommendations?
These statements differ from existing recommendations in order to simplify decision-making when failed tracheal intubation or failed oxygenation is encountered in the unconscious/induced patient.
Incidence and scope of the problem
Management of the difficult and failed airway in the unconscious/induced patient
The primary approach to tracheal intubation: “Plan A”
The alternative approach to tracheal intubation: “Plan B” in the adequately oxygenated patient
Failed tracheal intubation in the adequately oxygenated patient
Failed oxygenation: the emergency strategy
Tracheal intubation confirmation
The obstetric airway: special considerations
The pediatric airway: special considerations
Documentation following an encounter with a difficult airway
Education in the management of a difficult airway
Summary of recommendations
Bedside predictors of difficult tracheal intubation are imperfect. Accordingly, when general anesthesia (GA) is induced despite predictors of difficult intubation, many cases prove unchallenging. Conversely, unanticipated failure of tracheal intubation by direct laryngoscopy or other technique can occur when no such challenges were expected. Encountering difficult tracheal intubation in the unconscious patient is a concern, as many studies involving several specialties have documented increasing patient morbidity with multiple tracheal intubation attempts.1-5
Other hazards associated with difficulty in airway management have been highlighted in recent publications. Studies of closed legal actions6-8 related to airway management and the recent 4th National Audit Project (NAP4) of the Royal College of Anaesthetists and the Difficult Airway Society in the United Kingdom9,10 have helped direct attention to problem areas. In the NAP4 study, a prospective registry was created of major complications related to airway management occurring over a 12-month period in all 309 National Health Service hospitals in the United Kingdom. Complications were reported if they led to death, brain damage, need for emergency surgical airway, unanticipated intensive care unit (ICU) admission, or prolongation of ICU stay.9 The results of the audit provide considerable insight into causes of airway management-related morbidity and potential areas for improvement.
This first of two publications addresses airway management in the unconscious patient when difficult tracheal intubation is encountered. The second publication will focus on options and the approach to the patient when difficult airway management is anticipated.11 Taken together, the articles are intended to assist the practitioner with recommendations for airway management when confronted with a difficult or failed airway, regardless of where in the hospital an airway intervention occurs.
The Canadian Airway Focus Group (CAFG) was originally formed in the mid-1990s and published recommendations for the management of the unanticipated difficult airway in 1998.12 Four of the original CAFG members rejoined the current iteration, and the first author invited an additional 14 clinicians with an interest in airway management to participate. The current Focus Group includes representatives from anesthesiology, emergency medicine, and critical care.
Topics for review were divided among the members, and participants conducted a literature review on their topic(s). Electronic literature searches were not conducted according to a strict protocol, but participants were instructed to search, at a minimum, Medline and EMBASE databases together with the Cochrane Central Register of Controlled Trials (CENTRAL). Search strings were determined by individual participants. A worksheet was completed for each topic with details of the search strategy, a synopsis of the relevant studies, an overall summary of findings, the perceived quality of evidence, and the author’s suggestion(s) for strength of recommendation (see below). Once finished, worksheets were made available to the CAFG membership on a file hosting service.
The Focus Group convened regularly by teleconference, and face-to-face meetings occurred twice during the 24 months taken to complete the process. Worksheet authors presented their topics to the members, who then arrived at consensus on overall quality of evidence and any recommendations. In the event that evidence was of low quality or altogether lacking, “expert opinion” by consensus was sought. Finally, a draft of the completed manuscript was distributed to all members for review prior to submission.
The strength of a recommendation and the accompanying level of evidence were modelled after the GRADE system, as per previously published criteria.13,14 When made, formal strength of recommendations adhere to the following descriptors:
Strong recommendationfor – most patients should receive the intervention; most patients in this situation would want the recommended course of action;
Weak recommendationfor – most patients would want the suggested course of action, but some would not; the appropriate choice may vary for individual patients.
Strong recommendationagainst – most patients should not receive the intervention; most patients in this situation would not want the suggested course of action;
Weak recommendationagainst – most patients would not want the suggested course of action, but some would; the appropriate choice may vary for individual patients.
Three levels of evidence were applied,13 as follows:
Level of evidence A (High) – systematic reviews of randomized controlled trials (RCTs), RCTs without important limitations, or observational studies providing overwhelming evidence;
Level of evidence B (Moderate) – RCTs with limitations, observational studies with significant therapeutic effect;
Level of evidence C (Low) – RCTs with significant limitations, observational studies, case series, or published expert opinion.
When a level of evidence is not specifically supplied in this manuscript, recommendations reflect the consensus opinion of the authors.
The following definitions of terms are presented to clarify their use in the text. Some definitions have changed from the 1998 iteration of these recommendations to reflect the increased use of alternatives to direct laryngoscopy (DL) and ventilation with a supraglottic device (SGD).
Difficult airway: A difficult airway can be defined as one where an experienced provider anticipates or encounters difficulty with any or all of face mask ventilation, direct or indirect (e.g., video) laryngoscopy, tracheal intubation, SGD use, or surgical airway.
Difficult face mask ventilation: It has been suggested that inadequate mask ventilation may be more difficult to recognize than its complete absence.15 Although various definitions relating to difficulties with mask ventilation have been proposed,16-18 ease of mask ventilation is best described as a continuum from no difficulty to impossible. Difficult face mask ventilation may be signified by manipulations required for its facilitation, including adjustments of the head and neck, the use of adjuvants (e.g., an oral or nasal airway), use of exaggerated jaw lift, two-handed face mask application, and the assistance of a second operator.
Difficult laryngoscopy: Laryngeal exposure using DL is generally quantified using the Cormack-Lehane grade19 or one of its modifications.20,21 Most authorities agree that grade 1 and 2 views, where most or some portion of the glottis is seen, represent easy DL, while grade 3 and 4 views represent difficult and failed DL, respectively, even if tracheal intubation itself succeeds. The same classification can be employed when indirect techniques, such as video laryngoscopy, are utilized. Regardless of the technique used (DL or indirect laryngoscopy), the specific device should always be described in addition to the view obtained, the number of attempts, and the ancillary maneuvers required to achieve the result.
Difficult tracheal intubation: The success of direct or indirect laryngoscopy and tracheal intubation should be assessed independently, regardless of the technique. Difficult tracheal intubation can be defined as one or all of the following:12
Multiple attempts or more than one operator required;
An adjunct such as a tracheal tube introducer (“bougie”) is required to facilitate tracheal intubation;
An alternative intubation device is required after unsuccessful use of the primary, “Plan A” device.
A common reason for difficulty with tracheal intubation is a poor laryngeal view; however, if a Cormack-Lehane 1 or 2 view is obtained but difficulty occurs with directing or advancing the endotracheal tube (as may happen with video laryngoscopy), it is reasonable to describe this in some form of narrative. Alternatively, difficulty can be quantified using a scale based on several parameters.22
Difficult SGD use: Difficult or failed oxygenation and ventilation with an SGD may result from difficulties accessing the patient’s mouth or hypopharynx, achieving a seal,23 or ventilating the lungs.
Difficult transtracheal surgical airway: A surgical airway can be achieved by percutaneous needle-guided cannula methods or by an open operative technique. A difficult transtracheal surgical airway is one that requires excess time or multiple efforts.
Failed airway: Defining a failed airway helps serve notice to the clinician that a different course of action may be needed to minimize the potential for harm to the patient:
Failed tracheal intubation can be defined as failure to achieve successful tracheal intubation in a maximum of three attempts, irrespective of the technique(s) used.
Failed oxygenation (“cannot intubate, cannot oxygenate” [CICO])24 has occurred if, in the face of failed tracheal intubation, the patient cannot be successfully oxygenated by employing face mask or SGD ventilation.
Extubation of the difficult airway: Extubation is unsuccessful when a tracheal tube is removed but requires unanticipated replacement. This replacement (including tracheal tube exchange) can be difficult or fail. A clear definition of difficulty does not exist, but it is reasonable to assume that the difficulty further contributes to rather than resolves a deteriorating situation. A high-risk extubation can be described on two axes: the risk of not tolerating extubation and the risk of re-intubation being difficult or unsuccessful. Extubation of the patient with a difficult airway is addressed in the second article in this series.11
Incidence and scope of the problem
The published incidence of difficult airway management interventions varies substantially (Table 1). Although different definitions, patient populations, and clinician experience make these figures difficult to compare directly, a few trends emerge. Perhaps one of the more significant trends is the higher occurrence of difficulty encountered in locations outside of the operating room (OR).
Approximate incidence of difficulty with various airway interventions – by hospital location
Management of the difficult and failed airway in the unconscious/induced patient
Most airway management is performed in an unconscious patient, usually pharmacologically induced for surgical anesthesia. Outside the OR environment, a critically ill patient may be induced for the sole purpose of securing the airway or may already have been unconscious on initial presentation.
Airway management in the induced surgical patient may involve SGD or face mask ventilation, tracheal intubation, or rarely, a primary cricothyrotomy or tracheotomy. Difficulty may be encountered with any of these modalities and should be met with an appropriate response.
The primary approach to tracheal intubation: “Plan A”
For the unconscious/induced patient requiring tracheal intubation, the clinician’s primary “Plan A” approach may have been facilitated by DL or an alternative to DL, such as video laryngoscopy. Alternatives to DL may be chosen as the primary approach due to anticipated difficulty with DL, their utility in teaching, or clinician preference. The chosen technique should be suited to the context of patient anatomy and pathophysiology, operator familiarity, and the practice environment. The probability of first-attempt success should be maximized by familiarity with and attention to equipment and adjunct (e.g., malleable stylet or tracheal tube introducer) preparation, patient positioning, and optimal pharmacotherapy.51
Response to difficulty encountered in the unconscious patient
Difficult direct laryngoscopy: If a poor view is obtained during attempted DL despite proper positioning of the patient and the laryngoscope blade tip, optimizing maneuvers should occur, such as application of external laryngeal pressure (Strong recommendation for, level of evidence B). Unless contraindicated by C-spine precautions, additional head lift (to accentuate lower neck flexion and head/upper neck extension) may also be helpful.52-54
External laryngeal pressure is effective at improving the view during DL.55-63 This maneuver is distinct from cricoid pressure, applied to the cricoid cartilage to help prevent passive regurgitation of gastric contents. In studies, cricoid pressure resulted in no improvement64-66 or a worse64,67-69 view with DL; hence, a recommendation can be made against its use for the sole purpose of improving the view during DL if used instead of laryngeal pressure (Weak recommendation against, level of evidence C). External laryngeal pressure and head lift can be performed sequentially during the first attempt at DL.
There is little evidence that an automatic blade change is an effective strategy for a second attempt at DL unless a specific anatomic finding during the initial laryngoscopy suggests a benefit. Examples include a long, floppy epiglottis that could be directly elevated with a longer curved, or straight blade, or a suspicion that a Macintosh blade is too short to completely advance into the vallecula, thus failing to engage the underlying hyoepiglottic ligament.
The tracheal tube introducer has been extensively studied as an adjunct to DL. It is an effective aid to tracheal intubation faced with a restricted view during DL20,25,38,70-74 and may also be useful with some video laryngoscopes. If a restricted (e.g., Cormack-Lehane grade 2b or 3)19,20 view obtained during DL persists after optimization maneuvers such as external laryngeal pressure or additional head lift, use of a tracheal tube introducer should be considered (Strong recommendation for, level of evidence B). The CAFG recommends immediate availability of a tracheal tube introducer at all airway management locations.
Difficult video laryngoscopy: There are three independent tasks with video laryngoscopy, namely, laryngeal exposure, delivery of the tracheal tube to the laryngeal inlet, and advancement within the trachea. Use of a video laryngoscope will generally result in a good laryngeal view, although blades with more angulation or curvature will enable better exposure. The following techniques can facilitate passage of the tracheal tube: preparing a tracheal tube with a preloaded stylet with a curvature matching that of the video laryngoscope blade, partial withdrawal of the blade to provide a wider visual field, and deliberately not seeking a full view of the larynx before attempting passage of the tube. Once placed through the glottic opening, withdrawing the stylet 5 cm will help circumvent impingement of the tracheal tube tip on the anterior tracheal wall, permitting gentle tube advancement. Rotation of the tube may also address impingement. Video laryngoscopes with channeled blades (e.g., Airtraq®, Ambu® AWS, and KingVision™) also exist to facilitate delivery of the tracheal tube. Failure to achieve a view of the larynx with video laryngoscopy can be minimized by suctioning the oropharynx prior to initial blade insertion.
Difficult face mask ventilation: Difficult face mask ventilation of the unconscious patient before or between tracheal intubation attempts should be addressed with a graduated response, including placement of an appropriately sized oropharyngeal and/or nasopharyngeal airway, use of a two-handed mask hold, and exaggerated head extension, unless contraindicated (Strong recommendation for, level of evidence C).
The two-handed face mask hold facilitates ventilation by projecting the mandible anteriorly into the mask, which pulls the tongue forward and further opens the airway. It also provides an improved mask seal. Ventilation can be provided by an assistant or by the anesthesia machine ventilator if the patient is in the OR.
Cricoid pressure may make face mask ventilation difficult, especially if applied with excess force.75 If cricoid pressure has been applied and difficult face mask ventilation is deemed unresponsive to the foregoing measures, progressive release of pressure should be considered (Weak recommendation for, level of evidence C).
If difficult or impossible face mask ventilation persists despite corrective maneuvers, a SGD should be placed or tracheal intubation should be undertaken if not already attempted.15,76,77 Failure to ventilate with a SGD can often be resolved by ensuring an adequate depth of anesthesia, appropriate (e.g., no more than 60 cm H2O) cuff inflation, reinsertion of the device with a fully deflated cuff, or placement of a larger SGD.
Unsuccessful primary approach to tracheal intubation
An attempt at tracheal intubation may be unsuccessful despite optimized conditions and technique. In the induced/unconscious patient, this will most often be followed by face mask ventilation or, optionally, placement of a SGD. The success of oxygenation by face mask or SGD ventilation in this context dictates subsequent actions (Fig. 1). As long as oxygenation is non-problematic, the situation is stable, and if deemed appropriate, time exists for additional careful attempts at tracheal intubation. Conversely, the failure of face mask ventilation or a SGD to maintain adequate oxygenation after a failed attempt at tracheal intubation indicates a failed oxygenation/CICO situation (represented in the Emergency pathway on the right-hand side of the Fig. 1 flow diagram).
Flow diagram: difficult tracheal intubation encountered in the unconscious patient. SGD = supraglottic device
With non-problematic oxygenation, a second attempt at tracheal intubation can occur using the primary “Plan A” technique, but only if it is reasonable to presume that the factors contributing to the initial unsuccessful attempt can be addressed during the subsequent attempt. For example, an unsuccessful primary attempt at intubation using video laryngoscopy may yield information about the ideal curvature of a tracheal tube with preloaded stylet required for a second attempt.
The alternative approach to tracheal intubation: “Plan B” in the adequately oxygenated patient
An alternative “Plan B” approach to tracheal intubation should be employed if the primary approach is unsuccessful, if oxygenation remains non-problematic, and if further intubation attempts are planned. Experienced providers will often proceed to the alternative approach after only a single failed attempt with the primary device, recognizing the low incremental probability of successful intubation with a second attempt using the same device. In general, the alternative approach should be used after no more than two failed attempts at tracheal intubation using the primary approach and should employ a different device or operator.
Numerous alternatives to DL, used alone or in combination, have been proven effective in obtaining an improved view of the larynx and/or enabling successful tracheal intubation when DL is unsuccessful (Table 2). Many of the devices presented in Table 2 are indirect (e.g., video) laryngoscopes, although other techniques are also effective in experienced hands. Equally, there is also some evidence that DL-facilitated intubation may succeed should primary use of some of these same alternatives fail.78,79 As such, an argument can be made that these alternative devices should complement and not necessarily replace DL at this time. Irrespective of the technique chosen, proficiency demands elective experience in human subjects.
Effectiveness of a selection of alternatives to direct laryngoscopy in the difficult airway
There should be a reasonable expectation that the selected “Plan B” technique will address the reason, anatomic or otherwise, for failure of the primary approach. As with the primary approach, each use of the alternative device should be optimized, and a second attempt using the same device should occur only if made with a substantive change, e.g., a change in the size of the device, altered endotracheal tube/stylet conformation, or use by a more experienced operator. All clinicians with a mandate for airway management should be familiar with at least one alternative technique (e.g., video laryngoscopy) to DL to enable tracheal intubation (Strong recommendation for, level of evidence C), and such equipment should be immediately available. When difficult or failed DL is encountered, proceeding with a “Plan B” alternative intubation technique without awakening the elective surgical patient is common practice and is probably safe, provided that oxygenation remains unchallenged.
Failed tracheal intubation in the adequately oxygenated patient: exit strategies
Limits to tracheal intubation attempts
Evidence continues to emerge that patient morbidity increases with the number of attempts at tracheal intubation (Table 3). Mainly derived from the critically ill population, it must be acknowledged that there is marked heterogeneity in harmful “outcomes” reported in these studies (e.g., aspiration, hypoxemia, hypotension, trauma etc.), including composite outcomes. Furthermore, there is variable use of neuromuscular blockade, and it is unclear if the apparent risk relates to the number of attempts required, additional exerted force, or the associated delay in successful intubation. Nevertheless, the studies do provide a warning that the number of attempts at tracheal intubation should be minimized, irrespective of practice location. Incremental risk must be assumed with each failed attempt such that a second or third tracheal intubation attempt should occur only if a different tactic is used and there is a reasonable expectation of success. Proceeding with more than three attempts at tracheal intubation requires compelling justification.
Adverse effects associated with multiple attempts at tracheal intubation
With the evidence of harm accruing from multiple attempts at tracheal intubation, an argument can be made for always including first-attempt success rates in future studies of intubation devices, techniques, or skills acquisition.
Failed tracheal intubation: exit strategies
Three failed attempts at tracheal intubation should be taken as an indication to declare a failed intubation situation. This should signal the team to pause and consider an exit strategy, to avoid repetitive ineffective intubation attempts that might result in harm to the patient. In the adequately oxygenated unconscious/induced patient, a number of exit strategies exist:
Awakening the patient. The option of allowing the induced oxygenated patient to wake after failed tracheal intubation should be considered when feasible (Weak recommendation for, level of evidence C). Once awake and cooperative, awake tracheal intubation can be attempted in the spontaneously breathing patient. Alternatively, an elective surgical case could be deferred or potentially performed under regional or infiltration anesthesia. Oxygenation should be maintained with face mask or a SGD until the patient emerges from general anesthesia. Awakening the patient may not be possible or appropriate in an emergency, during an attempted resuscitation, or if the patient cannot cooperate with awake intubation or surgery under regional anesthesia. While there is no evidence to support the contention that awakening the elective surgical patient will confer an outcome benefit when tracheal intubation has failed, this option is supported by expert consensus to prevent deterioration to a failed oxygenation, “cannot intubate, cannot oxygenate” scenario.
Proceeding with surgery (or temporizing an emergency situation) using face mask or SGD ventilation. As an exit strategy for failed tracheal intubation in the induced/unconscious patient, the benefit of proceeding with surgery under face mask or SGD ventilation must exceed the risk of foregoing tracheal intubation. In general, this will be easier to justify for brief or urgent surgeries, although risk of aspiration must be considered. If surgery proceeds under face mask or SGD ventilation, a plan should exist for difficulty with or failure of oxygenation during the case. The critically ill non-surgical patient temporized with face mask or SGD ventilation will likely still require tracheal intubation or a surgical airway, sooner rather than later.
Obtaining equipment or additional expert help for a further controlled attempt at tracheal intubation. There is no doubt that minimizing tracheal intubation attempts is a sound principle. Nevertheless, the goal of engaging an exit strategy is not necessarily to prohibit more than three intubation attempts so much as to serve as a warning that further attempts may be attended by increasing patient harm and decreasing chances of success. Consequently, an “exit strategy” attempt at tracheal intubation should occur only with a high likelihood of success and a low probability of creating complications. For example, if a SGD had been placed after three failed attempts at tracheal intubation, bronchoscopy-aided intubation could have ensued via the SGD once an appropriate flexible bronchoscope became available. Alternatively, if additional expert help had been available, another attempt at intubation could have occurred with the same or a different device, being mindful of the need to avoid traumatizing the airway during the attempt.
Proceeding with surgical access. In rare circumstances, it may be appropriate to proceed with surgical access (cricothyrotomy or tracheotomy) following failed tracheal intubation in the adequately oxygenated unconscious/induced patient. This may be required if awakening the patient is not an option, i.e., most often in urgent or emergency situations.
Failed tracheal intubation may be apparent and an exit strategy engaged before three attempts at intubation have occurred, even after a single unsuccessful attempt.
Failed oxygenation during attempted tracheal intubation: the emergency strategy
Failed oxygenation (“cannot intubate, cannot oxygenate” [CICO]) exists following failed tracheal intubation if the patient cannot be successfully oxygenated by optimized face mask or SGD ventilation (Fig. 1). Three corrective measures are vital: immediate recognition, a call for help, and preparation for proceeding rapidly with a surgical/transtracheal airway (most often cricothyrotomy in the adult patient).
Due to the rarity of this situation, clinicians commonly exhibit a lack of situation awareness when failed oxygenation/CICO is encountered, having become fixated on multiple unproductive attempts at tracheal intubation or SGD placement. The failure to recognize failed oxygenation/CICO and respond appropriately has been shown to delay cricothyrotomy, resulting in cerebral hypoxia and cardiac arrest.6,9 It is imperative that all members of the assembled team be empowered to call for help or raise the need for emergency cricothyrotomy.
The Focus Group was reluctant to recommend a specific arterial oxygen saturation (SaO2) trigger for cricothyrotomy in a failed oxygenation/CICO situation. Nevertheless, given the sigmoid shape of the oxyhemoglobin dissociation curve, as SaO2 descends through 90%, the rate of desaturation will accelerate if efforts at oxygenation remain unsuccessful. A failed oxygenation/CICO situation with a rapidly declining SaO2 despite maximum attempts at oxygenation should be taken as an indication for cricothyrotomy, especially with the onset of bradycardia.172,173
Published case series174-176 and reports38,177-180 have described successful rescue oxygenation in failed oxygenation/CICO scenarios with placement of a SGD. Although recommended by national guidelines in many countries,12,17,172,181,182 evidence is lacking on whether outcome is improved with attempted SGD placement prior to cricothyrotomy in failed oxygenation/CICO situations. Regardless, if failed oxygenation/CICO occurs, one attempt should be made at placing an appropriately sized SGD familiar to the operator, unless this has previously failed (Strong recommendation for, level of evidence C). During this SGD attempt, a second individual should simultaneously prepare equipment and the patient’s neck for cricothyrotomy. If oxygenation is not restored via the SGD, immediate cricothyrotomy should proceed without further attempts at either SGD placement or transglottic tracheal intubation (Strong recommendation for, level of evidence C). As it takes longer than cricothyrotomy, retrograde intubation is not recommended in failed oxygenation/CICO scenarios.
For emergency subglottic transtracheal access, cricothyrotomy is most often recommended in adults over tracheotomy, particularly when performed by a non-surgeon. This is advocated because the space is less vascular and more readily palpable.
Cricothyrotomy can be categorized as surgical or non-surgical. Surgical cricothyrotomy involves the use of a scalpel to incise the skin and cricothyroid membrane, with placement of a small (e.g., 6.0-mm internal diameter [ID] in the adult) endotracheal or tracheostomy tube. Other instruments needed for the procedure may include a tracheal hook, a Trousseau dilator, or a tracheal tube introducer.183
Non-surgical cricothyrotomy involves one of two options: percutaneous insertion of a wide bore (≥ 4-mm ID) cannula by either cannula-over-needle or Seldinger wire-guided (e.g., Melker) techniques, or percutaneous insertion of a narrow bore (≤ 2-mm) intravenous-type cannula. Narrow-bore cricothyrotomy with jet ventilation requires a high-pressure ventilation source in adults (not universally available in all airway management locations); it is more likely to result in breath stacking, barotrauma, catheter kinking, or dislodgement, and does not provide airway protection with a cuff. Of the available options, it is associated with the highest complication and failure rates.6,9,10 Unless the clinician is very experienced with jet ventilation, this suggests that options in failed oxygenation/CICO in the adult patient should be limited to either the percutaneous needle-guided wide-bore cannula or the open surgical technique (Strong recommendation for, level of evidence C). Both percutaneous wide-bore cannula and open surgical choices allow the desirable option of placing a cuffed tracheal cannula/tube.
There is some evidence that the percutaneous needle-guided wide-bore cannula technique may be less effective than the open surgical procedure.9,10,184 Nevertheless, a recent survey suggested that Canadian anesthesiologists were most comfortable with a percutaneous technique.185 On balance, we recommend that adult cricothyrotomy should proceed with either a percutaneous needle-guided wide-bore cannula or an open surgical technique, governed by operator preference and equipment availability. Even so, mindful of the significant reported failure rates of the percutaneous techniques, clinicians must be prepared for immediate conversion to an open surgical technique should the percutaneous needle-guided technique fail.
Recent studies suggest that anesthesia providers may have difficulty with correctly identifying the cricothyroid membrane using external landmarks.186,187 This may argue for always beginning cricothyrotomy with a 3-cm vertical midline incision over the presumed location of the cricothyroid membrane (Weak recommendation for, level of evidence C), at least in the patient with indistinct external landmarks. The cricothyroid membrane may then be more accurately identified within the incision, and the cricothyrotomy can continue with either a needle-guided wide-bore cannula or surgical technique.
As one of the major complications of cricothyrotomy placement is false passage, correct cannula or tube location must be objectively confirmed using capnography or endoscopy.
Even if administering (or re-dosing) a neuromuscular blocking agent is not indicated as part of the initial management plan, once a failed oxygenation/CICO situation occurs, it should be considered to address possible laryngospasm and facilitate face mask ventilation (Weak recommendation for, level of evidence C).48 Secondly, if bradycardia should occur, administration of epinephrine or atropine may forestall cardiac standstill. In both instances, these actions are to be delegated to an assistant and must not delay cricothyrotomy.
As an infrequently-performed yet life-saving procedure, all airway managers must acquire and maintain cricothyrotomy skills through educational programs. Cricothyrotomy equipment should be readily accessible, and all clinicians and ancillary staff should know its location.
Tracheal intubation confirmation
The persistent presence of exhaled carbon dioxide “appropriate to the clinical circumstance” provides objective confirmation of tracheal intubation.12 Visualization of a tracheal tube between the cords or endoscopic visualization of the subglottic airway through a tracheal tube can provide additional confirmation.12 Chest rise and auscultation, tube misting, chest radiography, and pulse oximetry are not robust indicators of successful tracheal intubation.
In the NAP4 study, many complications of airway management reported in the emergency department (ED) and ICU were related to unrecognized esophageal intubation or tracheal tube dislodgements. The inconsistent use of capnography for confirmation of tracheal intubation or the lack of continuous capnographic monitoring of already intubated patients was judged contributory.10 Thus, capnographic confirmation of tracheal tube placement should occur for all hospitalized patients (Strong recommendation for, level of evidence B), and ongoing continuous waveform capnographic monitoring should occur for the duration of intubation and ventilation (Strong recommendation for, level of evidence C). The latter recommendation will facilitate early detection of tube dislodgement as well as inadvertent hyper- or hypoventilation.
Additionally, NAP4 found that the absence of a capnographic waveform in the setting of cardiac arrest was sometimes incorrectly ascribed to the absence of pulmonary perfusion without consideration of either esophageal intubation or a completely obstructed tracheal tube or trachea.9,10 This occurred in OR, ED, and ICU environments. In actual fact, the first 30 min of cardiac arrest with adequate chest compressions is often associated with an attenuated but present capnography trace when the tracheal tube is correctly situated and unobstructed.188 A flat capnograph should prompt exclusion of a misplaced or blocked tracheal tube.
Continuous capnographic monitoring has also been recommended for patients without tracheal intubation who are undergoing deeper levels of procedural sedation (e.g., Ramsay sedation scores 4-6).189
The obstetric airway: special considerations
A higher incidence of failed tracheal intubation has been reported in the parturient than in the general surgical population.31,32,190 Nevertheless, in series originating in jurisdictions with either a high volume of obstetrical general anesthetics or coverage limited to senior trainee or consultant anesthesia staff, the incidence of failed intubation is more consistent with that of general surgical cases.30,191,192 This should not induce complacency, however, as multiple issues can converge and potentially contribute to airway-related morbidity in the parturient193 (Table 4). To help mitigate these factors, it is essential that obstetrical units have appropriately trained staff and airway equipment that is immediately accessible and of the same quality and type (e.g., video laryngoscopes) as that used in the main surgical ORs of the facility (Strong recommendation for, level of evidence C).
Factors with the potential to have an adverse impact on airway-related morbidity in the parturient
Difficult and failed tracheal intubations may be avoided by the more frequent use of regional anesthesia for obstetric surgical procedures.192,201,202 High levels of anesthetic skill and experience facilitate effective and rapid neuraxial anesthesia in many emergency situations.202 On the other hand, as general anesthesia rates continue to fall, there is ongoing concern that trainees are not being adequately exposed to airway management of the parturient—many tertiary care centres now typically have general anesthesia rates of 5-7% for Cesarean delivery.32,202
Avoiding a bad airway-related outcome – first steps: Antenatal airway screening of all parturients should ideally occur to identify potential challenges.30,203-205 Once a parturient with difficult airway anatomy is identified, good communication is crucial. A plan should be formulated with the attending obstetrician with the understanding that, if operative delivery is likely, it should occur under controlled conditions. Early placement of an epidural catheter should be considered. The catheter should be tested to confirm its efficacy so that rapid conversion to a surgical level of anesthesia can occur for emergency Cesarean delivery. If the epidural is not working and time permits, it should be re-sited. Once the need for general anesthesia becomes apparent, the attending anesthesiologist should perform a formal assessment of the airway. The patient should be given pharmacologic anti-aspiration prophylaxis (Strong recommendation for, level of evidence C).
For induction of general anesthesia, all parturients should be appropriately positioned (e.g., “ramped” as needed to ensure the patient’s external auditory meatus is level with the sternal notch).206 Pre-oxygenation should occur using high flow rates of oxygen, with tidal volume breathing for three minutes, if time permits, or eight deep breaths over 60 sec207 (Strong recommendation for, level of evidence B). Cricoid pressure should be applied with induction and maintained as appropriate until the airway is secured. Succinylcholine is generally used to facilitate laryngoscopy if no contraindication exists. After induction, face mask ventilation with low insufflation pressures can occur while awaiting full onset of neuromuscular blockade. This is carried out both to extend oxygenated apnea time during tracheal intubation and to anticipate ease of face mask ventilation should a first attempt at intubation fail (Strong recommendation for, level of evidence C). Although this recommendation is a departure from the classic teaching of avoiding face mask ventilation during rapid sequence induction, the potential benefit of oxygenation probably outweighs the small risk of gastric insufflation causing regurgitation, especially if insufflation pressures are kept < 20 cm H2O.172,208
Failed primary attempt at intubation encountered in an induced/unconscious parturient: If a first attempt at tracheal intubation fails despite optimized technique, gentle face mask ventilation should be resumed (Fig. 2), and help summoned. Cricoid pressure should be maintained unless thought to be contributing to difficulty. Any difficulty with face mask ventilation should be met with a standard response of oropharyngeal airway insertion, two-handed mask hold with exaggerated jaw thrust, incremental release of cricoid pressure, and if necessary, SGD placement. If oxygenation is non-problematic, a second tracheal intubation attempt can occur with the following provisos: there must be a reasonable likelihood of success based on findings at the initial attempt and a different technique (e.g., video laryngoscopy) or operator should be employed.
Flow diagram: difficult tracheal intubation encountered after induction of general anesthesia in the parturient. SGD = supraglottic device
Exit strategy – failed tracheal intubation in the oxygenated parturient withNOfetal or maternal emergency: If tracheal intubation has failed and further attempts are predicted to have a low incremental likelihood of succeeding, the acuteness of the situation should be assessed. With no fetal or maternal emergency, the goal should be to maintain oxygenation and allow the parturient to emerge from general anesthesia. At that point, a decision can be made to revisit regional anesthesia (if not contraindicated) or proceed with awake tracheal intubation for general anesthesia. If face mask ventilation becomes difficult, a SGD should be placed to assist oxygenation while awaiting emergence from anesthesia. Use of a SGD with a second lumen to allow esophageal and gastric venting should be considered.
Exit strategy – failed tracheal intubation in the oxygenated parturientWITHfetal or maternal emergency: If persistent fetal distress or a maternal emergency exists following failed tracheal intubation in the adequately oxygenated parturient, Cesarean delivery and/or maternal resuscitation can proceed with face mask or SGD ventilation. Cricoid pressure should be released for SGD insertion. Most Focus Group members agree that re-applying cricoid pressure is unlikely to be beneficial after placement of a SGD with an esophageal port. After failed tracheal intubation for Cesarean delivery under face mask or SGD ventilation in an emergency, the obstetrician should be requested to make a generous surgical incision and to minimize fundal pressure or use vacuum extraction at the time of delivery209 (Strong recommendation for, level of evidence B). With uncomplicated and expeditious surgery, the procedure can be completed with face mask or SGD ventilation. If the case is complex, once the fetus has been delivered or the maternal emergency is stabilized, a cuffed tracheal tube can be placed under more controlled conditions (e.g., flexible bronchoscopic-aided intubation through a SGD), if required. If conditions permit, the surgery should be halted temporarily while the airway is secured, with optimized patient positioning and obstructing drapes moved aside.
A number of observational studies from outside North America have been published on using SGDs for elective Cesarean delivery in a select group of women. The subjects in these studies were of normal body mass index and well-fasted; they had anti-aspiration prophylaxis and underwent quick uncomplicated surgery. Although each study used a different version of the Laryngeal Mask Airway (LMA™), they were consistent in reporting a high rate of successful SGD placement and ventilation.44-46 In North America, with general anesthesia reserved mainly for emergency cases and with parturients typically having a higher body mass index, SGDs cannot be recommended for elective Cesarean delivery at this time (Strong recommendation against, level of evidence B). Nevertheless, these and other studies190 do support the early use of a SGD in any airway rescue scenario in the parturient (Strong recommendation for, level of evidence B).
Emergency strategy – failed intubation, oxygenationNOTpossible with face mask or SGD ventilation: Following a failed attempt at tracheal intubation, the failure to oxygenate the parturient with face mask or SGD ventilation (failed oxygenation/CICO) will also quickly result in fetal compromise. As with the general surgical patient, the default response to this scenario is cricothyrotomy, with a parallel bridging attempt at oxygenation with a SGD if not already tried. Once the patient is re-oxygenated via SGD or cuffed cricothyrotomy cannula, Cesarean delivery or further resuscitation can occur if a fetal or maternal emergency exists; however, if the situation is now stable, optionally, the patient can be awakened and a plan can be made for definitive care.
It must be emphasized that the failed oxygenation/CICO scenario implies a complete inability to oxygenate the patient. In this situation, the parturient will undergo rapid oxygen desaturation, indicating why further attempts at tracheal intubation are contraindicated and also why it would be impractical to allow the mother to wake.
Extubation and the postpartum period: Recent maternal mortality statistics from both the United States and United Kingdom indicate a shift in many airway catastrophes from induction of general anesthesia to the postpartum period, i.e., at emergence, in the postanesthesia unit, or when applied for postpartum surgical procedures.210,211 Heightened vigilance during these phases is clearly required.
The pediatric airway: special considerations
Respiratory complications continue to be a major source of morbidity in children requiring airway management.212,213 Despite this, difficult DL is rare in an otherwise healthy child. In an audit of 11,219 pediatric general anesthetics in a tertiary care centre, the incidence of difficult DL (Cormack-Lehane grade 3 or 4 views) was 4.7% in children less than one year of age and 0.7% in children older than one year.214 In another audit of 24,165 anesthetics in a tertiary care pediatric centre, the frequency of unanticipated difficult tracheal intubations was 0.24% in children less than one year of age and 0.07% in children older than one year.213 These figures may reflect a higher than expected incidence compared with that encountered in community hospitals due to referral bias.
Unexpected difficult face mask ventilation is also rare in pediatrics. When difficult mask ventilation is encountered, causes such as laryngospasm or gastric distension must be considered. Clinicians should include the unexpected in their differential diagnosis, such as congenital airway anomalies or airway obstruction by foreign bodies.215 The pediatric airway is very susceptible to trauma when compared with the adult airway, and repeated attempts at intubation may result in more swelling and subsequent airway compromise. Rapid desaturation during apnea and a lack of patient cooperation are additional significant considerations.
Video laryngoscopy: Many case reports describe video laryngoscopy facilitating successful tracheal intubation in children with difficult airways. As with adults, the majority of current studies show that use of certain video laryngoscopes can facilitate an improved glottic view when compared with DL in pediatric patients with a reassuring airway exam. However, time to intubation is either unchanged or prolonged.216-219 In one pilot study in pediatric patients with known or anticipated difficult airways, use of the GlideScope Cobalt™ resulted in a significantly improved glottic view compared with DL in 17 of 18 patients, although tracheal intubation failed when using the device in three of the 18 patients.220 Despite the lack of published pediatric studies, video laryngoscopy has the potential to be useful in the pediatric difficult airway.
Cuffedvsuncuffed tracheal tubes in children: There is no direct evidence that use of a cuffed tracheal tube in children will cause more subglottic injury or iatrogenic stenosis than an uncuffed tube.221,222 Use of a cuffed tracheal tube will minimize need for re-intubation,221 decrease the potential for loss of effective ventilation,223 and may protect against micro-aspiration.224 As long as close attention is paid to maintaining an adequate air leak (i.e., occurring at < 20-25 cm H2O) and/or monitoring cuff pressure, a recommendation can be made to use cuffed tracheal tubes for all difficult or emergency pediatric tracheal intubations (Strong recommendation for, level of evidence B).
SGDs in the difficult pediatric airway: Apart from case reports, little published evidence exists on the use of SGDs in the setting of difficult DL, difficult airway, or failed oxygenation/CICO situations in children. Case series support the use of SGDs, such as the LMA Classic™ and the air-Q® Intubating Laryngeal Airway, as conduits for intubation when difficult pediatric DL is encountered or anticipated.99,100,225-227 In most of these series, intubation was facilitated with flexible or semi-rigid endoscopy through the SGD. In a failed oxygenation/CICO situation, as with adult recommendations, an attempt should be made to oxygenate the pediatric patient with a SGD while equipment is being prepared for a surgical airway.
Transtracheal/surgical airway: Failed oxygenation/CICO situations are rare in children. The best strategy for emergency transtracheal oxygenation in children under 8-10 years of age remains unclear. In this population, the cricothyroid space is underdeveloped, leaving needle tracheotomy or surgical tracheotomy below the cricoid ring as the only options for transtracheal access. Depending on the pathology (e.g. subglottic stenosis, tracheal foreign body), rigid bronchoscopy may be the intervention of choice. In children older than eight to ten years of age, the vertical span of the cricothyroid space enlarges sufficiently to accommodate several of the commercially available cricothyrotomy products, although some of these devices have been associated with tracheal damage in animal models.228,229
The few reports on emergency transtracheal airway access in children under age 18 vary greatly in circumstances, equipment used, and patient age.9,230-233 Experience with transtracheal catheters placed for elective pediatric surgical procedures suggests that, despite controlled conditions, use of jet ventilation through such catheters is associated with a significant rate of complications, including barotrauma.234-236 Animal237,238 and bench239 modelling indicate that adequate oxygenation can be provided through transtracheal catheters without the use of jet ventilation.
In children younger than eight to ten years in a failed oxygenation/CICO situation, help should be summoned, and if not already attempted, a SGD should be placed while equipment is readied for surgical or needle tracheotomy (or rigid bronchoscopy, when indicated) (Strong recommendation for, level of evidence C). For the needle tracheotomy option, a kink-resistant240 catheter specifically made for this purpose should be used. Oxygenation can be provided via an Enk Oxygen Flow Modulator™ (Cook Medical, Bloomington, IN) with a flow rate of 1 L per year of age239 and an inspiratory-to-expiratory (I:E) ratio sufficient to allow expiration. As full expiration of tidal volume will not occur through the transtracheal catheter, continued attempts at airway-opening maneuvers and securing a definitive airway are essential.
Documentation following an encounter with a difficult airway
Appropriate documentation should be completed following every airway intervention, difficult or otherwise. The record should make specific mention of ease of face mask or SGD ventilation, the device used to perform tracheal intubation, the view obtained, and the number of attempts (Strong recommendation for, level of evidence C).
If airway management is difficult once, it seems intuitive that subsequent attempts will also be difficult, although patient, operator, or equipment factors may differ significantly. There is some evidence that a previously designated difficult or failed DL or intubation does confer a higher likelihood of encountering similar circumstances on a subsequent occasion.29,241,242 However, pertinent high-level prospective outcome studies using precise definitions are currently lacking, and may never be published. Even so, experts agree that it seems likely that good documentation and dissemination of difficult airway information may reduce critical airway events. The CAFG advocates a multi-layered strategy appropriate to the local system when a difficult airway situation has been encountered. At a minimum, this should include clear and accurate documentation in the patient’s medical record, personally informing the patient and the patient’s surgeon, and providing a difficult airway letter to the patient with copies to both the chart and the primary care provider.
Electronic recording and alert systems are advances over traditional handwritten records. In-hospital alert bracelets and local or national databases (e.g., the MedicAlert Foundation) should also be considered. Such databases have the advantage of being widely accessible without restriction of space or jurisdiction.
While subjective, the trigger for invoking this multi-layered strategy may include factors such as an inability to visualize the larynx, very difficult or impossible face mask ventilation, or opinion that future airway interventions would occur most safely with the patient awake.
Copies of a difficult airway alert letter (e.g., Appendix 1) should be stocked in locations where airway management regularly occurs. The content and structure of information contained in airway alerts should be clear and complete to maximize both patient safety and the potential for future database research.