Airway anatomy and physiology are altered in obesity, and an understanding of these changes is key to appropriate airway management. Longitudinal studies of pulmonary function have shown reduction in pulmonary tests with obesity. The functional residual capacity (FRC) is reduced by the conduct of general anaesthesia. In the obese, the resting metabolic rate, oxygen consumption and also carbon dioxide production are all increased, compounding the reduction in FRC. In addition to acting as an oxygen store, FRC is important in splinting small airways. Respiratory mechanics are affected even in moderate obesity. Prediction of difficulty: Mallampati score and neck circumference are better predictors than body mass index (BMI) and a history of obstructive sleep apnoea (OSA), but their predictive value is not strong. Difficult mask ventilation and difficult intubation are uncommon. Awake intubation is worthwhile if difficulty is expected, because of the rapid desaturation problem.

This chapter discusses difficult airway, causes of difficulty, patient factors, and types of difficulties. One of the principal difficulties in predicting airway problems under anaesthesia is that in most unexpected cases there are no symptoms. The symptoms associated with obstructed sleep apnoea (OSA) syndrome should be sought in suspected cases. Anaesthetists should be aware of the symptomatology (and signs) of impending airway obstruction. The chapter briefs about special investigations such as 'Quick look' laryngoscopy, ultrasound and radiology. Sleep apnoea patients in particular may well be at greater risk in the postoperative period than at induction, whilst some types of surgery are notorious for engendering airway difficulty post-operatively; facio-maxillary and anterior cervical surgery are examples. Rheumatoid and acromegalic diseases of the larynx are particularly prone to post-extubation obstruction, so that the smallest possible size of tracheal tube should be used.