M. Popat

Difficult Airway Society guidelines for management of the unanticipated difficult intubation

Problems with tracheal intubation are infrequent but are the most common cause of anaesthetic death or brain damage. The clinical situation is not always managed well. The Difficult Airway Society (DAS) has developed guidelines for management of the unanticipated difficult tracheal intubation in the non‐obstetric adult patient without upper airway obstruction. These guidelines have been developed by consensus and are based on evidence and experience. We have produced flow‐charts for three scenarios: routine induction; rapid sequence induction; and failed intubation, increasing hypoxaemia and difficult ventilation in the paralysed, anaesthetised patient. The flow‐charts are simple, clear and definitive. They can be fully implemented only when the necessary equipment and training are available. The guidelines received overwhelming support from the membership of the DAS.

Difficult Airway Society Guidelines for the management of tracheal extubation

Summary Tracheal extubation is a high-risk phase of anaesthesia. The majority of problems that occur during extubation and emergence are of a minor nature, but a small and significant number may result in injury or death. The need for a strategy incorporating extubation is mentioned in several international airway management guidelines, but the subject is not discussed in detail, and the emphasis has been on extubation of the patient with a difficult airway. The Difficult Airway Society has developed guidelines for the safe management of tracheal extubation in adult peri-operative practice. The guidelines discuss the problems arising during extubation and recovery and promote a strategic, stepwise approach to extubation. They emphasise the importance of planning and preparation, and include practical techniques for use in clinical practice and recommendations for post-extubation care.

Evaluation of airway equipment: man or manikin?

The past decade has seen significant changes in the area of airway management. The difficult airway continues to be an elusive problem, with an incidence that has remained largely unchanged and with complications arising from its management that remain a leading cause of anaesthetic morbidity and mortality [1]. The anaesthetic profession has responded with the publication of structured guidelines for difficult airway management [2]. Industry has not lagged behind, with a proliferation of new airway devices aimed to provide anaesthetists with alternatives to conventional airway management techniques. Cook listed 14 different types of supraglottic devices in 2003 [3], whilst a recent meta-analysis mentioned another 13 types of intubating aids including six videolaryngoscopes, two optical bougies and two airway conduits [4]. Add to that new designs of tracheal tubes, exchange catheters, stylets, lightwands and bougies and one has a long list that has probably grown by the time this editorial is in print. There has also been a move towards single-use equipment and for every device that is developed, one can be certain that a disposable version will soon follow. So, how does the discerning modern anaesthetist decide which device to use? In this era of evidencebased medicine, it should simply be a matter of looking at the supporting research. The gauntlet has been taken up rather enthusiastically by anaesthetists whose prolific articles are rivalled only by the burgeoning number of devices. This decade has also seen changes in the way research is conducted. The Research Governance Framework [5] was introduced in an attempt to regulate and maintain the quality of published research. The Central Office for Research Ethics Committees (COREC) was established in 2000 in order to streamline the research ethics process and in 2007 was incorporated along with the local research ethics committees (REC) into the National Research Ethics Committee (NRES) [6]. The process of setting up a clinical trial in humans is complex, and obtaining ethical approval is a difficult and longwinded process that can, at best, take up to 3–6 months. To add to the difficulties involved in conducting clinical research, shift patterns and limitation of trainees’ working hours result in many trainees’ completing their training without ever being involved in a single research project. What, then, should be the minimum evidence to label an airway device as efficacious and fit for purpose? Unlike introducing a new drug, there are no requirements for airway devices to undergo trials in humans before being introduced into the market. Cook, addressing this question in an editorial in Anaesthesia [3], suggested that a new airway device should undergo a threestage process: in stage 1, devices would be evaluated ‘on the bench’ and in specifically designed manikins; in stage 2, a rigorous pilot study would take place (in humans) to determine whether the device is effective and safe; and in stage 3, the device would be compared in a randomised controlled trial (in humans) against the current gold standard for the procedure for which it is expected to be used (in the case of supraglottic airways, the ‘classic’ laryngeal mask airway). Stage 1 would probably not require ethical approval; stages 2 and 3 would require both ethical approval and written consent. Many researchers have addressed these difficulties by finding an innovative solution: manikin studies. It is quite easy to see why manikin studies are attractive to researchers. Not all research ethics committees consider approval necessary for these studies and if approval is applied for it is usually easily obtained [7–10], as the issues around participant information, consent and recruitment involve staff and not patients. Furthermore, there are no adverse effects that might potentially halt the trial and the study can be completed in days, rather than months or years. There is certainly an important place for manikin studies in anaesthesia. For example, in some studies patients are not essential and manikins will suffice [11, 12]; others may require conditions that cannot be recreated easily in patients and manikins can offer an excellent alternative [13–15]. However, we are disturbed by a growing trend amongst researchers to circumvent Cook’s suggested stages 2 and 3, by extrapolating results from the evaluation of new airway devices on manikins to humans. We conducted a search using ‘manikins’ or ‘mannequins’ as keywords in the PUBMED database (http://www. ncbi.nlm.nih.gov/sites/entrez?db=pub med) and the websites of five premier anaesthetic journals, from January 2000 to July 2010. The results were analysed for studies in which manikins were used to evaluate or compare airway devices. A total of 57 such publications were found: 40 in Anaesthesia, 10 in the European Journal of Anaesthesiology: three each in the British Journal of Anaesthesia and Anesthesia and Analgesia; and one in Anesthesiology. The newest entry into this arena is the paediatric manikin: a search for ‘paediatric manikin’ studies comparing airway devices generated four papers in the last 2 years. Dare we say that having grown tired of comparing adult devices in adult manikins, researchers have now turned their attention to paediatric devices in paediatric manikins? This is exemplified by a recent publication [8] that looked at minimum and optimum light requirements for laryngoscopy in paediatric anaesthesia, in which data were obtained from 50 anaesthetists performing laryngoscopy on a child manikin. The authors had published a study [9] in Anaesthesia, 2011, 66, pages 1–9 .....................................................................................................................................................................................................................

The effect of neuromuscular blockade on the efficiency of mask ventilation of the lungs.

Summary We conducted a two‐part study to assess the practice of withholding neuromuscular blockade until the ability to ventilate the lungs using a bag and face mask (mask ventilation) has been established following induction of anaesthesia. The first part of the study consisted of a postal survey (71% response rate) of 188 anaesthetists in the Oxford region to assess their current practice. Thirty per cent of respondents always checked mask ventilation before administering a neuromuscular blocking drug, whereas 39% of respondents (all them consultants) never did this. A further 31% only did so in the case of known or anticipated difficulty with the airway. In the second part of the study, we measured inspired (VTI) and expired (VTE) tidal volumes before and after neuromuscular blockade in 30 patients undergoing general anaesthesia. The ratio VTE/VTI was used as a measure of the efficiency of ventilation. There was no difference in VTE/VTI before [mean (SD) 0.47 (0.13)] and after [0.45 (0.13)] neuromuscular blockade. We conclude that neuromuscular blockade does not affect the efficiency of mask ventilation in patients with normal airways.

The i‐gel™ airway for ventilation and rescue intubation

However, continuous intravenous midazolam infusion is another commonly used agent that will preclude BSD testing and it is almost certain that a similar inconsistency and confusion exists. Accumulation of midazolam and its active metabolite, 1-hydroxymidazolam glucuronide, are known to occur in critical illness, especially in the presence of renal impairment and it may take several days for adequate elimination to occur [5, 6]. In the absence of a clear understanding of how to determine the absence of pharmacological sedation it is logical to explore the feasibility of ancillary investigations to assist with or determine BSD diagnosis. The draft revision of the Code of Practice does indeed mention ancillary investigations such as fourvessel angiography, transcranial Doppler, magnetic resonance angiography, positron emission tomography and evoked potentials. However, the draft was unable to provide significant support for their use due to the lack of clear evidence of their role. I believe it is vital that we start to record how many UK patients fail to undergo BSD testing due to persisting sedation by adding this data to the Potential Donor Audit. There is a need to reach consensus on the use of ancillary investigations in the diagnosis of death and on the correct method for the assessment of potential residual sedation caused by longer acting agents. We can then move significantly closer to the goal of allowing all brain stem dead patients to donate if that has been their expressed wish.

Use of the bougie in simulated difficult intubation. 2. Comparison of single-use bougie with multiple-use bougie*

Summary We studied the success rates for tracheal intubation in 32 healthy, anaesthetised patients during simulated grade IIIa laryngoscopy, randomised to either the multiple‐use or the single‐use bougie. Success rates (primary end‐point) and times taken (secondary end‐point) to achieve tracheal intubation were recorded. The multiple‐use bougie was more successful than the single‐use one (15/16 successful intubations vs. 9/16; p = 0.03). With either device, median [range] total tracheal intubation times for successful attempts were < 54 [24–84] s and there were no clinically important differences between these times. We conclude that the multiple‐use bougie is a more reliable aid to tracheal intubation than the single‐use introducer in grade IIIa laryngoscopy.

Determination of the site of tracheal tube impingement during nasotracheal fibreoptic intubation.

This study examines the incidence and site of tracheal tube impingement during nasotracheal fibreoptic intubation, and the efficacy of anticlockwise tube rotation to overcome the problem. Forty‐three patients underwent fibreoptic‐assisted nasotracheal intubation using a preformed nasal tube, and a second fibrescope was used to observe any obstruction to passage of the tracheal tube. Impingement occurred in 10 cases, with the most common site being the right arytenoid cartilage. Rotation resulted in successful intubation in all 10 cases, but proximal rotation did not always result in an equal degree of rotation at the tube tip. We conclude that the site of impingement for nasotracheal intubation with preformed nasal tubes is located at the posterior structures of the laryngeal inlet and that anticlockwise rotation is a simple and effective solution.

Comparison of fibreoptic‐guided orotracheal intubation through classic and single‐use laryngeal mask airways*

We compared times to intubate the trachea orally and success rates using two fibreoptically assisted techniques in 42 healthy patients with normal airways using (a) a 6.0‐mm nasal RAE tracheal tube passed through a classic laryngeal mask airway (CLMA group) or (b) a 6.0‐mm nasal RAE tracheal tube passed through a new disposable Portex Soft Seal laryngeal mask airway (PLMA group). The mean (SD) total intubation times were 82 (14) and 80 (17) s, respectively (p = 0.55). The success rates for intubation at the first attempt were similar (17/21 in the CLMA vs. 16/21 in the PLMA group; p = 0.50). We conclude that there is no clinically significant difference between the times to intubate the trachea or success rates using these two devices, but there may be other more subtle measures which might influence the choice of device in clinical practice. Finally, in the course of this study we developed a grading scale to describe the laryngeal views obtained when using a fibrescope passed through supraglottic airway devices.

Use of the bougie in simulated difficult intubation. 1. Comparison of the single-use bougie with the fibrescope.

We studied the success rates for tracheal intubation in 64 healthy patients during simulated grade III laryngoscopy after induction of anaesthesia, using either the single‐use bougie or oral flexible intubating fibrescope, both in conjunction with conventional Macintosh laryngoscopy. Patients were randomly allocated to either simulated grade IIIa or grade IIIb laryngoscopy, and also to one of the two study devices. Success rates for tracheal intubation (primary outcome measure) and times taken to achieve intubation (secondary outcome measure) were recorded. For the simulated grade IIIa laryngoscopy group, the fibreoptic scope was more successful than the bougie (16/16 successful intubations vs. 8/16; p = 0.02). For the simulated grade IIIb laryngoscopy group, the fibreoptic scope was also more successful than the bougie (8/16 successful intubations vs. 1/16; p = 0.02), but clearly use of the fibreoptic scope was not as successful as it had been in simulated grade IIIa laryngoscopy (p = 0.04). With either device, median (range) total tracheal intubation times for successful attempts with either grade of laryngoscopy were less than 60 s (19–109) and there were no clinically important differences. We conclude that the fibrescope used in conjunction with Macintosh laryngoscopy is a more reliable method of tracheal intubation than the single‐use bougie in both types of grade III laryngoscopy. This finding has implications for the management of patients in whom grade III laryngoscopy is encountered unexpectedly after induction of anaesthesia, and also for the management of patients previously known to have grade III view at laryngoscopy.

A comparison of a flexometallic tracheal tube with the intubating laryngeal mask tracheal tube for nasotracheal fibreoptic intubation using the two-scope technique*

We compared the incidence and site of impingement of a flexometallic tracheal tube with those of the re‐usable intubating laryngeal mask (ILMA) tube in 60 anaesthetised patients undergoing nasotracheal fibreoptic intubation for oral surgery. A two‐scope technique was used, observing the site of impingement with one scope whilst intubating with the other. The tubes were 6.0‐mm in females and 6.5‐mm in males. Impingement occurred with 10 (33%) flexometallic and 2 (7%) ILMA tubes (p < 0.032). In all but one case, the impingement was posterior to the right arytenoid cartilage. When impingement was observed, a single disempaction with a 90° anticlockwise rotational manoeuvre overcame impingement in every case except one, allowing successful intubation. We conclude that the incidence of impingement of the tracheal tube, and therefore of potential laryngeal trauma from nasotracheal fibreoptic intubation, is significantly greater with the flexometallic tube than with the ILMA tube.