Difficult Airway Society guidelines (2004)

I would like to comment on four aspects of the editorial accompanying the Difficult Airway Society (DAS) guidelines (Chambers, Anaesthesia 2004; 59: 631–3). Professor Chambers described the DAS guidelines as being drawn up by ‘a group of enthusiasts’. He is right: the four authors have shown enormous enthusiasm in creating these guidelines, from inception to publication; as have the Difficult Airway Society members, providing comment and support during this process. However, the authors are not primarily enthusiasts, they are experts. The consequences of poor airway management are potentially disastrous. However, airway obstruction is uncommon and the causes are multiple. Inevitably the guidelines are therefore based on sparse good quality evidence, often necessarily extrapolated from elective or mannequin work to emergency patient care. Some controversy is therefore not surprising. Who are the guidelines for? Are they principally for experienced anaesthetists and specialists in airway management, or trainees and those with less experience? There is concern, at present, that airway skills are deteriorating, leading to actual patient harm [1], with trainees most, but not solely, ‘at risk’[1]. Professor Chambers suggests the flowcharts have little to offer in acute situations and that problematic airway management should be ‘almost second nature’ to anaesthetists. To the novice SHO performing rapid sequence induction (RSI) alone, for the first or even the tenth time, it is probably not. A 3-month audit of 16 novice anaesthetists in Glasgow reported the airway management of 3039 cases. The chosen technique was face mask in 7.5%, tracheal tube in 39.5% and laryngeal mask airway in 53%. Six percent of laryngeal mask airway insertions and 10% of intubations (78% of which were subsequently grade 1–2 laryngeal view) failed. Facemask ventilation throughout a case and RSI were performed less than once per week per trainee [2]. The DAS guidelines are more didactic and specific than North American guidelines [3, 4], which with multiple junctions and choices at each junction lead to more pathways and less guidance. The DAS guidelines emphasise a four-point plan with each consequent on the earlier plan failing. Plan A: Initial intubation attempt. Plan B: Secondary intubation attempt. Plan C: Maintain oxygenation and ventilation and bale out. Plan D: Invasive techniques for ‘can’t intubate, can't ventilate' (CICV). There is guidance on when a plan should be deemed to have failed. If the plan teaches nothing else it should be praised for this clear sensible, universal approach. Key elements include the use of transferable skills, routinely available equipment and the various laryngeal mask airways as part of plans B–D. There are several reasons why these elements are particularly appropriate in the UK: UK trainees spend more time unsupervised than in many other countries; frequently anaesthetizing emergencies out-of-hours and alone. Reducing training duration may compound this. Despite competency-based training, few hospitals have a formal ‘airway block’. Advanced airway skills acquisition is assumed to take place during other ‘blocks’. The increased use of supraglottic airways has reduced intubation experience [1] and UK trainees probably have more experience with laryngeal mask airways than anywhere else in the world. The structured A–D approach has further strengths: it is adaptable enough to allow local development of guideline variations while retaining the basic structure and it is suitable for assessment of competency-based training, examination and audit. Professor Chambers infers a need for better pre-operative assessment, a return to the basic skills of facemask ventilation and more use of succinylcholine. Features predictive of intubation difficulty may be present in as few as one third of patients who are difficult to intubate [5, 6] and a recent editorial questioned the usefulness of all attempts at prediction [7]. Facemask ventilation is clearly an essential skill. Although it may be heresy to some, one could argue that ventilation via a laryngeal mask airway is an intrinsically better technique where ventilation difficulties occur. Nurses, after 30 min of instruction and mannequin practice, achieved 30% larger tidal volumes with bag and laryngeal mask airway than anaesthetists with a bag and mask [8]. A prospective protocol whereby all ‘can’t intubate, can't ventilate' (CICV) cases were managed with a laryngeal mask airway, re-established the airway in 16 of 17 cases [9]. In another study, intubation or mask ventilation difficulties were managed with a gum elastic bougie (GEB) (for difficult intubation) or intubating laryngeal mask airway (for GEB failure or difficult mask ventilation) [10]. In 11 257 cases, 100 (0.9%) cases of difficulty occurred. The GEB enabled 80 intubations and the intubating laryngeal mask airway 13 (and in 15 cases enabled ventilation). The median time to secure the airway was less than 5 min. As regards succinylcholine, the argument continues as to the correct dose and, indeed, whether it should be used at all [11-13]. Professor Chambers takes issue with the apparent pre-eminence of invasive techniques in plan D (CICV). The guidelines do not advocate invasive techniques for failed intubation and difficult ventilation, but for ‘failed intubation and ventilation with increasing hypoxaemia’. They state ‘these techniques can have serious complications – use only in life threatening situations’. Further, they caution repeatedly against starting invasive techniques without ‘maximum effort to provide ventilation and oxygenation via facemask or LMA’ and ‘only in life-threatening circumstances’. Up to 28% of anaesthesia-related deaths are reported to be due to these circumstances [14]. Invasive techniques should not be undertaken lightly but many failed intubations are unpredicted, and failed intubation is often associated with difficult mask ventilation [15, 16]. All anaesthetists must be prepared and able to manage an unexpected CICV situation. This includes the ability to perform invasive tracheal access. The challenge is to develop appropriate off-patient training to ensure that appropriate familiarity is widespread [17, 18]. These guidelines are a starting point. No doubt, like the ASA guidelines, they will evolve. Individuals or institutions may wish to modify the guidelines to suit local caseload, skills and facilities. However the structure of the DAS guidelines with a clear plan whose duration is explicit, with a logical progression through a series of back-up plans is an excellent foundation for all guidelines. Perhaps in the future no anaesthetist will anaesthetise any patient without plans A, B, C and D being ‘almost second nature’. I was asked to comment on an early draft of the guidelines, though through computer error it is unclear if my comments ever arrived. I am not a member of the Difficult Airway Society. I have received free airway equipment for research from a variety of manufacturers and also a small honorarium for Intavent Orthofix, the manufacturers of laryngeal masks in 2000 for addressing a company meeting.