Airway management in obese patients

Summary

Airway management is often the principal concern of the majority of anaesthetists when presented with an obese patient for general anaesthesia. Many anaesthetists will be increasingly encountering obese patients requiring all types of surgery. With the expansion of bariatric surgery both worldwide and in the UK, there is now a greater evidence base to inform and guide airway management in the obese patient. This article aims to improve understanding of the term ‘difficult airway’ in the obese population and focuses primarily on evidence related to pre-operative airway assessment and intra-operative airway management in the obese patient.

Introduction

Anaesthesia in morbidly obese patients can present many challenges. The overriding concern of most anaesthetists however, is airway management, as traditionally, obese patients have been thought to be at greater risk of difficult airway and/or difficult intubation, when compared with the general population. There is plenty in the literature regarding this subject area, but the mundane is rarely reported, and so this article aims to clarify the incidence and objectively review, the evidence for difficult airway in the obese population.

The term ‘difficult airway’ has been defined by the American Society of Anesthesiologists (ASA) taskforce as the clinical situation in which a conventionally trained anaesthetist experiences problems with mask ventilation or tracheal intubation or both.¹ Difficult endotracheal intubation has also been defined by the ASA as more than 2 attempts at intubation or attempts lasting more than 10 min.

The literature concerning difficult intubation uses numerous different definitions of ‘difficult intubation’ and this lack of consensus translates to difficulty in comparing airway studies. Some authors use the Cormack and Lehane grading of 3 or 4 (C & L, grades 3–4) as an end-point to define difficult laryngoscopy and hence difficult intubation, in an attempt to simplify the issue. However ‘difficult laryngoscopy’ does not always equate with ‘difficult tracheal intubation’ and ‘easy laryngoscopy’ does not always equate with ‘easy intubation’.

Other definitions of the difficult airway include complete failure to intubate and more than three attempts to pass the endotracheal tube. Although the view at laryngoscopy is a frequently used definition, the relationship between the number of laryngoscopies, the number of tracheal intubation attempts and the degree of post-operative morbidity has not been clearly defined.²

The Intubation Difficulty Scale score³ has been used in several studies to assess difficult intubation and takes into account difficult laryngoscopic view, number of attempts required to intubate the trachea and other factors associated with difficulty. It is a validated objective scale producing a score that can be used to evaluate intubating conditions and techniques. It correlates with time to intubation and a Visual Analogue Scale (VAS) assessment of difficulty. A point is scored for each variable encountered. The variables used in the score are as follows:

• N₁ – number of additional attempts;

• N₂ – number of additional operators;

• N₃ – number of alternative intubation techniques used;

• N₄ – glottic exposure as defined by Cormack and Lehane;

• N₅ – lifting force applied during laryngoscopy;

• N₆ – need to apply external laryngeal pressure to improve view;

• N₇ – position of vocal cords at intubation.

A summary of how the IDS score is calculated and the interpretation of this score is given in Table 1.