The airway.

Abstract

Anaesthetists have a duty of care to provide safe and effective airway management. This is easily and safely achieved in most patients. Difficulties occur in a few patients. Morbidity and mortality as a consequence of management of these difficulties is a major cause of concern to anaesthetists worldwide [1-3]. Closed claims analysis indicates that there were avoidable factors in most cases [1]. A reduction in the incidence of these avoidable adverse outcomes requires a response from those institutions responsible for maintenance of standards and for training and from individual anaesthetists. Closed claims data in the US revealed that respiratory events accounted for the single largest class of injury. Three mechanisms accounted for nearly three quarters of the cases; inadequate ventilation (38%), oesophageal intubation (17%) and difficult tracheal intubation (18%). Caplan suggested that most outcomes were preventable with better monitoring and that improved strategies for management of difficult intubation were urgently required [1]. The American Society of Anaesthesiologists responded with the ‘practice guidelines for management of the difficult airway’ published in 1993 [4]. The Canadian Airway Focus Group (CAFG) developed strategies for management of unanticipated difficult airway in 1998 [5]. In the UK there are no national guidelines. The Royal College of Anaesthetists (RCA) has recommended that departments develop their own guidelines for management of failed intubation. The Difficult Airway Society (DAS) is currently developing guidelines for the management of unanticipated difficult intubation in the adult non-obstetric patient [6]. Practice guidelines are not intended as standards but they provide evidence-based recommendations derived by analysis of published literature and consensus opinion. Regular revision is necessary and the ASA guidelines have been updated several times [7, 8]. All guidelines strongly recommend the formation of specific strategies for management of difficult airway scenarios and have published algorithms to aid the anaesthetist's decisions in formulating a primary (Plan A) and back up (Plan B, C, etc.) plans. All emphasise the primacy of maintenance of oxygenation at all times and the need to avoid multiple attempts with the same technique. The CAFG and DAS algorithms, unlike the ASA ones, recommend the use of a small number of core techniques to execute each plan. The role of practice guidelines in patient safety can be evaluated by closed claims analysis. Currently, difficult airway claims are evaluated in a structured fashion with regard to whether the practice guidelines were followed or not [9]. Miller has summarised 98 such claims which predated the guidelines and use of LMA in the US [10]. A difficult airway was anticipated in 52% and unanticipated in 48% claims. In the anticipated group, there was no explicit information about a preformulated strategy in 28% (10/36) of cases. Repeated non-surgical intubating attempts were made in 77% of cases. Comparison of these data with post guideline claims should be available in the next few years and is eagerly awaited by the anaesthesia community. Although there are no equivalent studies in the UK, there is no room for complacency. An MDU publication in the early 1990s and a recent editorial [11] allude to continuing avoidable airway deaths in anaesthetic practice in the UK. The CAFG and DAS guidelines emphasise the importance of training programmes to ensure that trainees are competent in the core airway techniques recommended in their algorithms. There is evidence to support the teaching of specialised skills in ‘block rotation’[12]. This approach to airway training ensures that each trainee receives adequate exposure to both conceptual knowledge and necessary practical experience. In the USA, the Accreditation Council for Graduate Medical Education (ACGME) requires training programmes to provide significant experience with specialised techniques which include but are not limited to flexible fibreoptic intubation and laryngeal mask airway [12]. In the UK, the RCA has introduced competency-based modular training. An extensive airway syllabus is recommended but with no requirement for a designated airway module. It is expected that competency in airway management would be gained during other modules. An RCA Working Party recently concluded that there was no need for a designated person in each Trust to have specific responsibility for airway teaching skills [11]. Regional Advisers in Pain Management were recently appointed by the RCA. In contrast, requests by the DAS executive to appoint airway training co-ordinators for each School of Anaesthesia have been ignored. Only 27–33% of anaesthesia training programmes in the US and 28% in Canada provide a dedicated airway module [12-14]. In the US survey, modules last a month and take place in all years of training. All programmes taught fibreoptic intubation and about three quarters taught use of the lighted stylet and intubating LMA, but few trained in invasive rescue techniques. If airway training of future consultants is poor, we may expect an increased incidence of avoidable airway complications. In the UK, the RCA recommends standards of training but it is the responsibility of local departments and consultant trainers to provide training. Basic airway skills are important and should be taught by all consultants at every opportunity. Training in advanced skills such as fibreoptic intubation, intubating laryngeal mask and transtracheal techniques is a real cause for concern. Some of the skills are complex; training on live patients causes logistic problems, including equipment availability, adequate training time, suitable training lists and competent trainers. Airway techniques have traditionally been learned on the job and have used a ‘see one, do one, teach one’ approach. Techniques for management of the difficult airway were taught when these situations arose; consequently, teaching was occasional, incomplete and non-uniform. A variety of training methods have been devised to help overcome these problems [15]. One approach is to provide training on a variety of patient substitutes such as bench models and manikins. This approach avoids the ethical problems of using animals, cadavers and live patients and has been shown to be an effective means of teaching both basic skills and advanced techniques such as fibreoptic intubation, cricothyroidotomy and use of the intubating laryngeal mask [15]. Interactive manikins (patient simulators) can reproduce the conditions under which the skills learned by the trainee can be performed in a real life setting. Reinforcement of conceptual knowledge and behaviour, and management of infrequent events, such as failed ventilation, can be practised without risks to patients. The disadvantages are the cost and manpower requirements. A second approach is to enhance efficacy, provide safety and avoid complications when training takes place on patients. Most of the published work relates to fibreoptic intubation and has been extensively reviewed [15]. A third combined approach is to provide structured graduated training so that a complex skill is broken down into several steps, some of which can be learned on models and then reinforced on patients. This approach has been used in the author's and other departments to teach fibreoptic intubation [16-18]. Consideration of the issues relating to training in advanced airway techniques has resulted in a debate about consent. In the UK, the AAGBI recommends at least verbal consent for anaesthesia but not for each individual anaesthetic procedure, so long as it is performed routinely. It draws attention to the risk of restricted consent whereby a patient may give consent for anaesthesia but not for intubation. The question is whether techniques such as fibreoptic intubation may be considered routine and whether they pose additional risks. A working party set up by the Difficult Airway Society made the following recommendations after achieving consensus between its members (unpublished): Advanced airway techniques such as fibreoptic intubation and use of intubating laryngeal mask airway are now standard airway techniques and no longer research tools. Their use need not be confined to the management of the difficult airway, but deserves an equal place with rigid laryngoscopy in routine everyday practice. As for rigid laryngoscopy specific consent is not required for an advanced technique if the anaesthetist uses it regularly in his/her practice, unless it involves an anatomical route different from that required for the surgical procedure, e.g. nasal intubation or cricothyroid puncture when there is no clinical indication. Specific consent is desirable if the anaesthetist does not perform the particular technique regularly. This approach puts the issue of teaching advanced airway techniques on the same basis as other routine techniques such as regional block and invasive monitoring procedures. Learning curves to estimate the number of procedures which must be performed in order to reach an acceptable success rate have been produced for many airway techniques [15]. Numbers alone do not provide a basis on which to declare a trainee competent at a procedure and other methods such as objective structured assessment of technical skills (OSATS) – where the observer watches the trainee perform a procedure and scores them according to predetermined criteria have been proposed. Simulators may have a role in assessing competence in situations where conventional direct laryngoscopy is difficult or has failed. How should the anaesthetist transfer the guideline recommendations into his/her practice? The Union of European Specialists (UEMS) recommended that an individual specialist should have an up-to-date knowledge of and proficiency in 10 core topics including the ‘airway’. The recommendations include competency in strategies for difficult airway and failed intubation. What core skills should a consultant possess to achieve this goal? In my view, these include techniques to overcome four common scenarios: anticipated difficult airway, unanticipated difficult airway in routine and in rapid induction and the ‘can’t intubate, can't ventilate' situation. The process starts with airway evaluation. All guidelines recommend that pre-operative history and physical examination of the airway are performed on all patients. Predictive tests are used to identify difficulties in patients in whom there are no obvious abnormalities as a consequence of airway pathology. Yentis has described the characteristics of an ideal predictive test and its validation process [19]. Tests have moderate sensitivity but low specificity and a low positive predictive value. Yentis concluded that we should dispel the myth that airway assessment actually helps in predicting difficulty accurately but there is an important benefit in performing this ritual, namely, it forces the anaesthetist atleast to think about the airway and have a clear plan [19]. A false positive (the patient is falsely judged to be difficult to intubate) has very little consequences, whereas the false negative (the patient who turns out difficult despite our prediction) can have serious consequences. A few false positives may have a general advantage in that more awake intubations would be performed on easy patients, ensuring safety and providing training. Generally, multiple tests should be used and those listed in the latest ASA guidelines are recommended [8]. An unfortunate consequence of the incidence of false positives is that airway examination is often omitted and important findings are missed. There was no record of a significant airway history in 25% and the physical examination was incomplete in 22% of closed claims analysed [10]. The standard airway examination is designed to predict difficulties with the Macintosh technique. There is some information about prediction of difficult mask ventilation. One must also try to assess whether there is a probability of difficulty with the laryngeal mask airway, flexible fibrescope and surgical access, if these feature in the airway management plans. Anaesthetists should have strategies for dealing with the anticipated and the unanticipated difficult airway. Many new airway devices and techniques have been introduced in the last decade, each claiming a role in difficult airway management. Randomised controlled trials of different techniques in the difficult airway are not available because of its low incidence and lack of precise definitions. Cook has pointed out that new airway devices are introduced on the market without trials of clinical effectiveness and argued that this process should be changed [20]. Methods of gaining competence in these devices have been discussed. Short courses and workshops are a useful introduction but they should be followed up by routine practice. Successful outcome is determined less by the equipment than by the experience and the skill of the operator. Some recommended techniques for the four difficult airway scenarios are presented below. A primary technique (Plan A) must be formulated but preparations should be made to allow seamless progress to execution of subsequent plans. Consider the relative merits of securing the airway by surgical airway or tracheal intubation. In the case of intubation, consider whether Plan A should include awake intubation or intubation after induction of general anaesthesia. In the latter case, decide whether the patient should be paralysed or breathing spontaneously. Soon after the introduction of muscle relaxants we learnt that these drugs should not be used if there was any doubt about the ease of tracheal intubation. It is now appreciated that the safest strategy in these patients is to maintain consciousness until the airway is secured [21]. Almost all intubation techniques can be performed in the awake patient provided good airway anaesthesia has been achieved. There are compelling reasons to prefer the flexible fibreoptic laryngoscope for this purpose. The instrument offers flexibility to manoeuvre under vision through the most difficult pathological airway and permits immediate visual confirmation of the position of the tube. The ability to instil local anaesthetic and oxygen via the working channel are unique. The fibrescope can be used in all age groups for both oral and nasal intubation and facilitates the use of other devices. The success rate is very high. The safety and efficacy of fibreoptic intubation has been extensively researched and proven training methods exist. The author's experience of over 350 awake fibreoptic intubations confirm that with increasing experience, this technique is successful in the most difficult cases, some of which are considered contraindications by others [22]. The ability to perform awake fiberoptic intubation is also a useful back up plan after failed intubation. Mastery of fibreoptic endoscopy is useful in other situations such as checking the position of double-lumen tubes, elucidation of diagnostic problems in recovery room, tracheal tube exchange, percutaneous tracheostomy and diagnostic use in intensive care. A few patients will not co-operate for an awake intubation and plan A should include techniques under general anaesthesia, but spontaneous ventilation is essential whenever difficulty is anticipated. Local and regional anaesthesia are viable alternatives to general anaesthesia with tracheal intubation is some situations. However, the airway problem is not solved and the anaesthetist must have a predetermined plan to abort the procedure or secure the airway if the regional technique fails or proves ineffective. The Macintosh laryngoscope is commonly used to facilitate tracheal intubation. The first attempt should always be performed in optimal conditions, after ensuring adequate muscle relaxation, positioning of head and neck and the use of external laryngeal manipulation should be an integral part of this attempt [21]. An alternative technique using a gum elastic bougie and/or another blade will be needed if the view is grade 3 or 4. Many laryngoscope blades are available; the McCoy, straight blade and Bullard are of proven value. The value of these devices in patients with difficult airway problems is supported by a large number of publications [5]. The multiple-use gum elastic bougie (Eschmann introducer) technique combines simplicity of operation and high success rate with low cost and ready availability [23]. The technique is blind and should be used in the optimal way to ensure a high success rate and to avoid trauma. It is of limited value when it is not possible to elevate (grade 3B) [24] or visualise (grade 4) the epiglottis. Single-use disposable introducers have recently been introduced, but they are not as effective as the original multiple-use bougies [25]. The Lighted stylet [26] has been recommended in the CAFG guidelines. Flexible fibreoptic intubation is a more demanding technique in the anaesthetised patient but a high success rate has been achieved in experienced hands [27]. These techniques are performed in the apnoeic patient and adequate mask ventilation must be ensured between intubation attempts. Multiple attempts with the same technique should be avoided. If the techniques used in Plan A fail, then alternative techniques which facilitate ventilation both during and between intubation attempts should be used. ‘Dedicated airway devices’ facilitate tracheal intubation while maintaining airway patency [28]. Many supraglottic airway devices have been used but the laryngeal mask is the most frequently used and evaluated device. The techniques of use and the limitations of the classic laryngeal mask airway as a conduit for intubation are well known [16]. The intubating laryngeal mask airway was specifically designed to overcome these limitations and its use is recommended [29, 30]. It is preferable to use a fibreoptic technique to facilitate intubation through either of the laryngeal mask devices. The number of attempts with any device must be limited and the safest option is often to awaken the patient and then to perform an awake intubation. The option of continuing anaesthesia with the laryngeal mask is possible but is not a safe option when surgery can be postponed. The laryngeal mask airway is now used in many situations where tracheal intubation would formerly have been used. It is unclear whether this approach has reduced the number of failed intubations. Use of the LMA has clearly greatly reduced the number of routine tracheal intubations performed, to the extent that there is concern about training and maintenance of traditional airway skills [11]. This scenario should be managed in a different manner because the decisions and choice of techniques are influenced by the increased risk of aspiration, the application of cricoid pressure and the duration of paralysis with succinylcholine. The principles of optimizing the initial tracheal intubation technique and the use of the bougie and alternative blades are the same as during induction of anaesthesia for elective surgery. There is extensive literature on cricoid pressure, including the optimal technique, ideal force required and its effect on the performance of various airway techniques [31]. If intubation fails after a maximum of three attempts, then a failed intubation plan, with the aim of maintaining oxygenation and awakening the patient, should be initiated immediately. If the patient's life is in imminent danger from the surgical condition and it is essential to proceed with surgery, the traditional technique is to continue with mask ventilation and oral airway with continued application of cricoid pressure. Continuation of anaesthesia with a classic LMA is now an established technique [32], although not always effective. The Proseal LMA may prove to be the ideal device in this situation as it can provide improved protection against aspiration [33, 34] albeit at a cost of increased complexity of insertion. In the patient at risk of aspiration, the flexible fibrescope and the laryngeal mask devices cannot be included in the algorithm for intubation. Every intubation attempt increases the risk of aspiration and some techniques would be difficult to accomplish in the short duration of muscle relaxation provided by succinylcholine, so that there is a real risk of laryngeal spasm. This is usually the result of repeated attempts at intubation [1, 10]. Maximum efforts should always be made to achieve gas exchange with non-invasive techniques. These include the optimum use of face mask and airways, the laryngeal mask and possibly the Combitube [5, 21]. A decision to perform invasive techniques via the cricothyroid membrane must be made when these fail. Two techniques, cannula cricothyroidotomy with percutaneous jet ventilation and surgical (stab) cricothyroidotomy are recommended [35, 36]. Strategies should also be worked out for safe extubation. It is important to document details of the difficulties encountered and their management in the patient's notes and to arrange communication of these for the future care of the patient. Rosenblatt's survey of 472 anaesthesiologists in the United States to identify their preferred management techniques in 14 difficult airway scenarios involving co-operative patients revealed that experienced practitioners tended to use high-risk induction techniques [37]. The use of adjuncts to the direct laryngoscope or alternative devices was uncommon: in patients with previous difficult intubation, 60% would induce general anaesthesia and 59% would use direct laryngoscopy. A similar survey of practising Canadian anaesthesiologists conducted by Jenkins showed that direct laryngoscopy (48%) and fibreoptic bronchoscopy (34%) were the two most commonly used techniques for intubation [38]. Lighted stylets, intubating guides and rigid fibreoptic laryngoscopes, recommended in the Canadian guidelines, were rarely used. Kristensen's survey of Danish anaesthesiologists showed that 52–70% knew the basic principles of the ASA algorithm but only 25–50% would perform awake intubation if difficulty was anticipated [39]. The vast majority (> 67%) had no experience of using the flexible fibrescope for awake intubation despite its availability and 18–46% did not know how to oxygenate via the cricothyroid membrane. It is clear that most anaesthetists continue to use high-risk strategies as a consequence of a limited range of skills. Skills with the combination of the Macintosh laryngoscope, LMA and bougie are not sufficient core skills to allow safe airway management of all patients. Knowledge of airway management has increased greatly in the last decade and new tools and techniques have been introduced but many anaesthetists have failed to keep their skills up to date. An attitude of risk prevention can only be implemented with a sufficient range of skills. These skills can only be gained with the right attitude towards training and learning and should be our immediate goal to enhance safe airway management. I would like to thank Dr John Henderson for his helpful advice.