Airway management in critical illness: practice implications of new Difficult Airway Society guidelines

When a large international body such as the Difficult Airway Society (DAS) issues its fourth (or, depending on how one counts, its fifth) set of guidelines on airway management, there might be understandable concern about repetition or worse, contradiction. The recently- published guidelines on managing the airway in critically ill patients 1 joins past guidelines for failed tracheal intubation and extubation in adults, and for airway management in paediatrics and obstetrics (www.das.uk.com) 2. Yet, the content and approach remain fresh and unique; there is only the barest of necessary repetition and certainly no contradiction. There are also important implications, which its authors and DAS itself may not have fully considered, which we now address below. The new guidelines stress that the target group of patients is those who are ‘critically ill’, regardless of location. The implication is that this set of guidelines supervenes all other DAS guidelines, in the specific scenario of critical illness. However, this is not made explicit, and in some of the text there is an equal implication that messages from other DAS guidelines might continue to have a role. We feel this could be confusing to readers. Moreover, the guidelines do not define what is meant by ‘critically ill’. Although this apparent omission may have been intentional, because it allows the individual practitioner latitude in employing the guidelines, some clarification would have been helpful. In the broadest sense, this encompasses any patient so ill or badly injured that they might soon die and, therefore, it can be safely assumed that most patients will be classed as ‘critically ill’ if they fulfil the criteria for intensive or high dependency care admission, or require urgent airway management at emergency admission. It will be interesting to see if, in fact, colleagues will class stable patients with rapidly developing pathologies (e.g. those needing major surgery) who have a significant chance of later intensive care unit (ICU) admission as ‘critically ill’. If so – and it would be a reasonable decision – then the reach of these guidelines may be far greater than the authors anticipated. Distinct from all other DAS guidelines, these are designed to guide planning and are not failed in- tubation guidelines. A prerequisite to planning is the act of prediction. Hitherto, strategic planning for airway management has been hindered by the perception that a difficult airway ‘cannot be predicted’ 3. This view has recently been challenged by Pandit and Heidegger 4 who argue that binary prediction is both necessary and successful. This does not mean that all difficult airways can be predicted with certainty; nor that all airways predicted as difficult will be so. Rather, it means that it is possible to divide all airways into the ‘likely easy’ (when difficulty is extremely uncommon) and the ‘plausibly difficult’ (when difficulty is several thousand per cent more common than in the alternative group). Consistent with this, these new guidelines recommend a specific management plan when a critically ill patient is predicted to have a difficult airway. The authors suggest using the MACOCHA score as the basis for prediction (determined by Mallampati score, presence of obstructive sleep apnoea, cervical spine mobility, opening of mouth, coma, hypoxia and anaesthetist/non-anaesthetist practitioner 5). We do not take a view on the best score to use, but agree with the philosophy of identifying a plausibly difficult airway, distinct from the likely easy airway, and preparing an appropriate airway management plan. In the DAS guidelines, this tailored plan involves the early use of videolaryngoscopy, if available. Thus, it should become evident from later review of an anaesthetic chart that, where non-standard devices such as these were employed and an airway team assembled (see below), difficulty was expected. An alternative approach is simply to apply a generic management plan to all patients and then rely on existing failed intubation algorithms in the rare case of failure 6. This alternative is explicitly rejected by the new guidelines, as it has been in previous correspondence 6. Moreover, if this act of predicting the difficult airway in a binary manner becomes embedded in practice for the critically ill, then we anticipate that it will naturally be extended to binary airway prediction for all patients as an essential part of anaesthetic management. Despite the advocacy of videolaryngoscopy, the guidelines unashamedly stress that successful airway management does not rely solely on the introduction of new devices or even improved technical skills, but rather on human factors, a cohesive airway team, planning and communication. On one level, this has important implications for the strategy of DAS as an organisation. Until very recently, a main focus of DAS has been the development and investigation of devices. Discussions around ‘kit’ have dominated its popular annual meetings and device research has been at the root of its strategy 7. The strong implication of the guidelines’ statement is that DAS should now re-focus on a more holistic adoption of ‘oxygen-management’ or ‘hypoxia-prevention’ as its core mission, in which studies of equipment to manage the upper airway form just one aspect. We might anticipate and hope that DAS moves away from promoting research into ‘device A vs. device B’ and instead supports research into better understanding of hypoxia physiology, including studies of how interventions like transnasal humidified rapid insufflation ventilatory exchange (THRIVE) might work 8, or into relevant human factors, psychology or simulation research. Thereby, DAS might wish to evolve into a ‘difficult oxygenation society’ rather than a ‘difficult airway society’. Yet, readers should not jump to the conclusion that devices are to be regarded as irrelevant. The guidelines are forceful in their emphasis that videolaryngoscopy with a screen visible to all should be used early. Some large UK hospitals still have not purchased any videoloaryngoscopes, and many that have appeared to have opted for the cheapest possible optical devices that lack a visible screen 9. After publication of these guidelines, it is difficult to see how any hospital in an economically developed country can claim to provide safe anaesthesia for the critically ill unless it can demonstrate investment in suitable with-screen videolaryngoscopes and appropriate training in their use. Also, given the likely widening of the definition of who is ‘critically ill’ (see above), it will simply not suffice to purchase a single device that sits as a totem, unused and gathering dust in a cupboard, Moreover, the guidelines stress the need for second generation supraglottic airway devices (SADs). Again, hospitals relying purely on first-generation SADs should bear this in mind if they wish to be judged as providing optimal peri-operative care. The guidelines emphasise the role of bougies in patients with grade-2b or -3a laryngoscopy views. Not all bougies perform equally, so a range should be stocked, and that this should include the gum elastic bougie which, notwithstanding user preference, has been objectively established to perform best, over single-use versions 10. Additionally, the guidelines remind us that a stylet (a shorter, stiffer stick) is needed to pre-shape the tracheal tube for use with hyperangulated videolaryngoscopes. Experienced users will know to lubricate the stylet before shaping the tube, otherwise it can be very difficult to remove it after intubation. Perhaps it is the recommendations around the ‘airway team’ that will present the most radical change in practice. The guidelines specify several team models in which four, five or six members are assembled, with at least two ‘intubators’; presumably anaesthetists, although this is not specified. Note that gathering a team from the start, before any intervention, is quite distinct from ‘calling for help’ in an unanticipated failed intubation, as was the emphasis in previous DAS guidelines. This mandate for teams may come as a (welcome) surprise to many UK readers who are used to having just two members of the team – themselves and their anaesthetic assistant – even in a failed intubation scenario. Indeed, anecdotally, it has now been the norm for many years that UK consultants and other senior doctors work alone, in isolation, as much in NHS/public hospitals as in private practice 11. Whole theatre suites in the UK regularly function with staffing of just one anaesthetist per theatre, who may even be a trainee 12, 13, with no ‘spare’ anaesthetist. Additional assistance often comes with some luck, only after the most critical events have occurred. Clearly this aspect of the recommendations has profound implications for anaesthetic staffing and we hope the serious consequences of failing to meet the need will place pressure on hospitals to comply. There are several details concerning anaesthetic practice which we hope will inspire correspondence. The guidelines repeatedly refer to ‘rapid sequence induction’ (RSI) and ‘modified rapid sequence induction’ (MRSI). Although they are widely understood, we are not convinced that these terms have ever been properly defined. In principle, a description of RSI would encompass the judicious use of a hypnotic and neuromuscular blocking drug in a way that facilitates rapid anaesthesia and intubation of the trachea without antecedent mask ventilation of the lungs, coupled with cricoid pressure to prevent regurgitation of gastric contents. In detail, the term RSI appears associated with: (a) pre-oxygenation; (b) use of a pre-judged dose of thiopental; (c) avoidance of opioids; (d) cricoid pressure; (e) administering suxamethonium; and (f) intubating the trachea before mask ventilation (and usually after the muscle fasciculations have subsided). Any departure from the detail of (a)–(f) might be regarded as ‘modified’. For example, the 5th National Audit Project (NAP5) on accidental awareness during general anaesthesia, noting the prevailing practice in its activity survey 14, suggested that propofol was a suitable alternative to thiopental, and that opioids could or should be included in RSI/MRSI 15. More recently, with the availability of sugammadex, there is also the option of rocuronium as the neuromuscular blocker. A consensus is emerging that cricoid pressure. The new DAS guidelines go further and advise that cricoid pressure should be removed even to facilitate SAD insertion 17. The guidelines also modify RSI to the extent that they advocate mask ventilation before intubation (after paralysis), and to perform it in between intubation attempts 18, 19. Consequently, perhaps we need to cease discussing notions of variously ‘modified’ RSI, and instead collectively to define what we mean by ‘RSI’ in the modern era. The DAS guidelines offer insightful recommendations for tracheal extubation, particularly in the context of ICU management, which echo those presented independently in a recent narrative review 20. The authors observe that ~15% of patients whose tracheas are extubated in the ICU require tracheal re-intubation within 48 h. They go on to recommend that extubation should, therefore, always be considered a ‘trial’, with an active plan for an immediate, difficult re-intubation; that is, assembling the airway team of four, five or six staff, etc., as discussed above. Specifically, the guidelines recommend that planned extubation of known difficult airways should only be performed in ‘daytime’ hours. All this builds on the technical advice provided in the previous DAS guidance on difficult extubation. The clear logic is that all patients requiring tracheal extubation who were judged critically ill at time of intubation, or who were not critically ill but underwent difficult airway management, should be regarded as difficult extubations and, therefore by default, may need potentially difficult and rapid re-intubation. These recommendations might greatly challenge the practice in some ICUs in the UK, where a practice of ‘fast track extubation’ may have become embedded. The practice probably originated with observations after cardiac surgery, but reports have described this practice after major transplant and lung surgery and, therefore, can be applied to any patient being considered for ICU admission 21. Many anaesthetists will have experienced being asked by ICU colleagues to try and extubate a surgical patient's trachea before transfer after ~18.00 h, mainly on the grounds that their gas exchange is adequate and, therefore, continued ventilation does more harm than good. The DAS guidelines no longer support such practice as routine, especially if the airway was initially difficult or has become so 20. Even if a decision is made to extubate before ICU admission so late in the day, the consensus from both the DAS guidelines and the previous narrative review 20 is that this should now only be attempted after a full risk assessment, assembling the four to six person airway team, all appropriate equipment and an active plan made for difficult, immediate re-intubation. Like so many of the others, this set of DAS guidelines has profound implications for clinical practice. For individuals, it creates a requirement routinely to predict the difficult airway with a binary conclusion on difficulty or not, and to act on the findings. This may, in turn, mean greater use of established technologies like with-screen videolaryngoscopes. On identifying a critically ill patient who is plausibly difficult, the important change in practice will be to summon the appropriate assistance and team from the start, and not just as a later ‘call for help’. Where difficulty has been anticipated, pressing on alone regardless will no longer be seen as a sign of skill or experience, but as recklessness or ignorance. ‘Fast track’ postoperative extubation after difficult airway management in the critically ill is generally inappropriate, and in any case, all planned tracheal extubations in this group are now recommended only in daytime hours with the recommended airway team with a plan for rapid re-intubation. For hospitals, the new guidelines will require an even greater focus on anaesthetic staffing. It can no longer be considered safe for workforce plans to rely on consultants or other doctors working alone with no spare anaesthetist in the hospital, let alone in the theatre suite. Hospitals will be expected to invest in videolaryngoscopes with visible screens, in addition to other suitable laryngoscopes, and to stock a range of bougies and stylets, as are needed for the proper use of these devices. Upgrades to at least second-generation SADs will be required. The DAS has not held back from offering impactful recommendations, which will undoubtedly become practice standards that promote patient safety. It is now up to the anaesthetic community and hospital management to make use of them. JP is the Deputy Scientific Officer of the Difficult Airway Society, but had no role in the development of the guidelines discussed. JP and MI are Editors of Anaesthesia. JP is Chair of the Safe Anaesthesia Liaison Group and Council Member, Royal College of Anaesthetists: the views expressed are personal and not of those organisations. No other competing interests declared.