Assessment of anaesthetists’ ability to predict difficulty of bag-mask ventilation

Abstract

Editor—I read with interest the Correspondence by Roberts and colleagues1Roberts S Cyna AM Walsh JP Davis JS Assessment of anaesthetists’ ability to predict difficulty of bag-mask ventilation.Br J Anaesth. 2013; 111: 676-677Abstract Full Text Full Text PDF PubMed Scopus (2) Google Scholar regarding the anaesthetists’ ability to predict difficult bag-mask ventilation (BMV). Their findings show unreliable preoperative prediction of quality of BMV after induction of anaesthesia. However, the authors do not specify how many patients had received a neuromuscular blocking agent at the time of assessment of BMV. Such information is important because there is considerable evidence that early muscle relaxation will facilitate BMV. The findings of a prospectively assessed algorithm for difficult airway management including 12 221 BMVs are one example in support of the benefit of early muscle relaxation on the quality of BMV.2Amathieu R Combes X Abdi W et al.An algorithm for difficult airway management, modified for modern optical devices (Airtraq laryngoscope; LMA CTrach™): a 2-year prospective validation in patients for elective abdominal, gynecologic, and thyroid surgery.Anesthesiology. 2011; 114: 25-33Crossref PubMed Scopus (126) Google Scholar Patients with indications for awake fibreoptic intubation were excluded. The algorithm required that patients with three and more risk factors for difficult airway management receive succinylcholine right after induction of anaesthesia without prior assessment of quality of BMV. There were 188 patients who qualified for this approach. After administration of succinylcholine, BMV was grade I (ventilation without need for an oral airway) or II (ventilation requiring oropharyngeal airway) in 175 (93%), grade III (difficult and variable ventilation requiring an oral airway and two providers, or an oral airway and one provider using pressure-controlled mechanical ventilation requiring 25 cm H2O) in 12 (6.3%), and grade IV (ventilation inadequate with no PE′CO2 measurement and no perceptible chest wall movement during attempts at positive pressure ventilation) in one patient (0.5%) (grades I and II, and grades III and IV being equivalent to scores <3 and 3 or more, respectively, used by Roberts and colleagues). Thus, of those 188 patients with predicted difficult BMV, barely 7% actually demonstrated difficult BMV. This is less than half the incidence reported by Roberts and colleagues.1Roberts S Cyna AM Walsh JP Davis JS Assessment of anaesthetists’ ability to predict difficulty of bag-mask ventilation.Br J Anaesth. 2013; 111: 676-677Abstract Full Text Full Text PDF PubMed Scopus (2) Google Scholar It is conceivable that the higher incidence in the latter report was caused by the absence of muscle relaxation at the time of assessment of BMV. In patients with <3 risk factors, the quality of BMV was assessed before administration of a neuromuscular blocking agent. After the administration of succinylcholine in 90 patients with BMV difficulty grade III, the quality of BMV improved by one grade in 56 (62%), and did not worsen in any of the remaining 34 patients. After administration of a non-depolarizing neuromuscular blocking agent in 12 003 patients with BMV difficulty grade I and II, the quality of BMV did not worsen in a single patient. These findings confirm previous ones showing that in patients with unimpaired3Goodwin MWP Pandit JJ Hames K Popat M Yentis SM The effect of neuromuscular blockade on the efficiency of mask ventilation of the lungs.Anaesthesia. 2003; 58: 60-63Crossref PubMed Scopus (67) Google Scholar or with a mix of unimpaired and moderately difficult BMV,4Warters RD Szabo TA Spinale FG DeSantis SM Reves JG The effect of neuromuscular blockade on mask ventilation.Anaesthesia. 2011; 66: 163-167Crossref PubMed Scopus (91) Google Scholar the quality of BMV either remained unchanged or improved after the administration of a neuromuscular blocking agent, but never worsened. During the past 25 yr, in the absence of indication for awake fibreoptic tracheal intubation, I have routinely administered the planned full dose of the neuromuscular blocking agent as soon as the patient went off to sleep. With this practice, I have rarely encountered impossible BMV. In my view, lack of administration of muscle relaxation immediately after induction of anaesthesia should be considered a predictor of difficult BMV. I fully agree with the authors’ statement that BMV is ‘a vital1, life-saving skill for anaesthetists’1Roberts S Cyna AM Walsh JP Davis JS Assessment of anaesthetists’ ability to predict difficulty of bag-mask ventilation.Br J Anaesth. 2013; 111: 676-677Abstract Full Text Full Text PDF PubMed Scopus (2) Google Scholar (although with the advent of supraglottic airway devices, the importance of BMV has somewhat diminished). However, BMV may iatrogenically be made difficult by the reluctance of early muscle relaxation. The authors of the 4th National Audit Project (NAP4) of the Royal College of Anaesthetists and The Difficult Airway Society5http://www.rcoa.ac.uk/nap4 (accessed 2 October 2013).Google Scholar make this point a couple of times in the context of difficult ventilation. None declared.