A patient presents for elective surgery with the following letter:
This 40-year-old male, 100 kg (220 lb), 170 cm (67 in) presented for elective surgery. History was remarkable for snoring and hypertension. Preoperative airway evaluation showed a Mallampati III/IV oropharyngeal view, normal inter-incisor and thyromental distances and moderately reduced cervical extension. Bag-mask ventilation was satisfactory. Three attempts at intubation were required. A Cormack-Lehane Grade III view was obtained and intubation was successful using an Airway Introducer (gum elastic bougie).
We have new practice guidelines for management of the difficult airway,1 but are we in agreement about to whom these guidelines apply? The above patient presents with a “Difficult Airway Letter,” but was his laryngoscopy “difficult,” or did it fail, since the larynx was not seen? Tracheal intubation was successful, but was this the result of skill or luck? Was this a “difficult airway” or a lucky patient?
After the introduction of the Miller and Macintosh laryngoscopy blades, advances in airway management stagnated for nearly three decades. We now have a variety of supraglottic devices that may avoid tracheal intubation, and several optical devices that make use of coherent fiberoptic bundles, prisms or video chips allowing us to see previously concealed structures. It is important that we make the appropriate adjustments in the terminology we use to describe what we do. Clear communication will reduce the probability of others repeating nonproductive strategies or subjecting patients to uncomfortable techniques that may not enhance their safety.
Preoperative bedside assessment of the airway continues to be advocated1 despite its poor specificity and sensitivity2 because any assessment is better than no assessment, and despite imperfect prediction, a seemingly problematic airway is more likely to be challenging than one that looks benign. Furthermore, it establishes that we have made an effort and helps us prepare for contingencies in the event of failure of our primary plan.
While a bedside assessment may fail to identify a difficult airway, evidence from Denmark demonstrated that a previous difficult or failed direct laryngoscopy is a strong predictor of subsequent difficulties or failure with an odds ratios of 22.9 (17.4-30.2, 95 percent CI) and 16.6 (11.9-23.2), respectively.3 Similarly, patients who experienced uneventful intubations by direct laryngoscopy were very likely to have an unremarkable subsequent experience.3 Thus, anesthesiologists must take previous difficulties seriously. This seems obvious, yet evidence exists that a known difficult airway is all too frequently managed with a routine induction, and when difficulties are encountered, there are persistent attempts using ineffective methods.4,5 The authors of the 4th National Audit Project of the Royal College of Anaesthetists and the Difficult Airway Society described the “failure to plan for failure” with its consequent poor outcomes. Crosby drew the following evidence-based conclusions: 1) difficult intubation remains a relevant issue; 2) there is little correlation between the airway evaluation and airway management strategy; 3) poor anesthetic practice contributes to adverse outcomes; and 4) criticism of adverse outcomes by experts is common.6
There is a growing body of literature suggesting that patients in whom intubation by direct laryngoscopy failed can be successfully managed using an alternative indirect method. Traditionally, this has been synonymous with flexible bronchoscopic intubation. And bronchoscopic intubation has generally meant awake intubation. We now have a variety of choices, including supraglottic airways as primary devices or conduits for intubation, rigid anatomically-shaped fiberoptic laryngoscopes (e.g., Bullard laryngoscope), lightwands and video laryngoscopes. All of these devices are independent of a line of sight and their success is more likely to be related to operator experience than the difficulty encountered with direct laryngoscopy. The evidence supporting the use of such devices should be interpreted cautiously:
Have they been evaluated in normal or abnormal airways?
Was the patient population similar to your own; indeed, were they evaluated in real patients or airway simulators?
Were the operators novices or experienced clinicians?
What training had they received prior to the study?
Were the outcomes clinically relevant?
A good or excellent laryngeal view is better than no laryngeal view but only insofar as it is associated with an increased successful intubation rate.
Two studies by Aziz and colleagues illustrate several of these points.7,8 Two centers participated in a database review of over 70,000 intubations and the electronic records were searched to identify patients in whom a GlideScope was used either as the primary or rescue device.7 They found that it was used mostly on patients with features suggesting a challenging direct laryngoscopy, and a total of 2,004 uses were identified. Features suggestive of such difficulty included patients with a Mallampati III or IV view, reduced thyromental distance, obese neck, neck pathology or radiation. The primary outcome was successful intubation on the first attempt, though repeated attempts were permitted. Overall, they observed that the GlideScope was quite effective in achieving success when used as a primary or rescue device. More interesting, however, was the difference between the outcomes at the two participating institutions – the center where the GlideScope was more readily available had significantly better outcomes. (Flexible bronchoscopic intubation failed in 10 patients and was successfully accomplished using the GlideScope in eight. The patients in whom GlideScope intubation failed were successfully intubated by direct laryngoscopy.)
When patients with at least one feature predictive of difficult (direct) laryngoscopy or a past history of such difficulty were prospectively randomized to intubation with a Macintosh or Storz C-MAC video laryngoscope, operators knowledgeable with both devices experienced greater first-pass success with the C-MAC (138/149 vs. 124/149; p=0.026).8 This represented a 52 percent reduction in the number of failed first attempts. Laryngeal views were markedly better in the C-MAC group with less frequent reliance of external laryngeal pressure and the need for a gum-elastic bougie. Shorter intubation times (13 seconds) were seen with direct laryngoscopy in those patients successfully intubated.
Generally, the quality of evidence supporting many of the airway practice guidelines is low, consisting largely of well-intended but biased expert opinion. In the end, devices don’t manage airways – airway managers do, and their skills and judgments are determined by their experience. The more often they use devices, the better they recognize the limitations of a tool and also how well it performs in their own hands. Reserving a device for salvage rather than routine use is likely to be associated with less satisfactory outcomes.
Let us return to our patient with the “Difficult Airway Letter”: the letter fails to identify the device that was originally used and by whom. We are forced to draw conclusions that may or may not be correct. Furthermore, we do not know whether there were any optimizing maneuvers done between attempts such as repositioning, the use of a stylet or selection of an alternative blade. Nonetheless, the clinician may be able to draw from his or her own experience the likelihood that intubation will be successful using an alternative to direct laryngoscopy and create conditions that are conducive to patient comfort and safety. An experienced and skilled video laryngoscopist most likely could manage the above patient after the induction of anesthesia. This includes optimal positioning for the first attempt, adequate pre-oxygenation and a strategy to manage unexpected failure. The decision to manage the airway prior to induction does not automatically imply election of the flexible bronchoscopic approach; however, it is important that the clinician retain his or her skills with this technique and seek out opportunities to refine it. It is commonly observed that, as video laryngoscopy becomes readily available, awake bronchoscopic intubation is less frequently performed. There are many situations when it remains the most appropriate technique and skill retention is essential for patient safety.
The intention of this discussion is not to diminish the value of the “Difficult Airway Letter” but rather to reinforce its possibilities. It is valuable only insofar as it informs the subsequent care provider precisely what was done initially and thereafter. It does not automatically dictate the need for either awake or bronchoscopic intubation. Indeed, it should dictate nothing other than to serve as an indication that a repetition of the previous method has a high probability of the same outcome – an unnecessarily difficult and potentially injurious encounter.
Richard Michael Cooper, M.D., F.R.C.P.C. is Professor, Department of Anesthesia, University of Toronto, Director, Anesthesia Airway Fellowship at Toronto General Hospital, Toronto, Ontario, Canada. He is President, Society of Airway Management.
1. Apfelbaum JL, Hagberg CA, Caplan RA, et al.; American Society of Anesthesiologists Task Force on Management of the Difficult Airway. Practice guidelines for management of the difficult airway: an updated report. Anesthesiology. 2013;118(2):251-270.
2. Shiga T, Wajima Z, Inoue T, Sakamoto A. Predicting difficult intubation in apparently normal patients: a meta-analysis of bedside screening test performance. Anesthesiology. 2005;103(2):429-437.
3. Lundstrom LH, Moller AM, Rosenstock C, Astrup G, Gatke MR, Wetterslev J; Danish Anaesthesia Database. A documented previous difficult tracheal intubation as a prognostic test for a subsequent difficult tracheal intubation in adults. Anaesthesia. 2009;64(10):1081-1088.
4. Rose DK, Cohen MM. The airway: problems and predictions in 18,500 patients. Can J Anaesth. 1994;41(5 part 1):372-383.
5. Cook TM, Woodall N, Frerk C, eds. Fourth National Audit Project of The Royal College of Anaesthetists and Difficult Airway Society. Major Complications of Airway Management in the United Kingdom: Report and Findings. London: Royal College of Anaesthetists; 2011. http://www.rcoa.ac.uk/node/4211. Accessed July 8, 2013.
6. Crosby ET. An evidence-based approach to airway management: is there a role for clinical practice guidelines? Anaesthesia. 2011;66(suppl 2):112-118.
7. Aziz MF, Healy D, Kheterpal S, Fu RF, Dillman D, Brambrink A. Routine clinical practice effectiveness of the Glidescope in difficult airway management: an analysis of 2,004 Glidescope intubations, complications, and failures from two institutions. Anesthesiology. 2011;114(1):34-41.
8. Aziz MF, Dillman D, Fu R, Brambrink AM. Comparative effectiveness of the C-MAC video laryngoscope versus direct laryngoscopy in the setting of the predicted difficult airway. Anesthesiology. 2012;116(3):629-636.
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