The airway in obese patients

Pulmonary physiology Diminished lung capacity Diminished vital capacity Decreased chest wall compliance Increased abdominal cavity contents Increased airways resistance Relative room air hypoxia and hypercapnia VQ mismatch from collapse of small airways Decreased FRC Increased O2 consumption and CO2 production

Resulting in: Decreased Oxygen Reserve Rapid desaturation during periods of apnoea

Gastrointestinal physiology Increased intra abominal pressure Hiatus hernias Reflux Larger gastric volume Lower pH of gastric contents INCREASED RISK OF ASPIRATION AND LUNG INJURY POST ASPIRATION

Predicting difficult airway Obesity does not necessarily predict difficult laryngoscopy and intubation - other factors may be more important than BMI Obesity does reliably predict DIFFICULT MASK VENTILATION If time allows consider awake intubation by an anaesthetist

Preoxygenation Elevate patient’s head to 25 degrees during preoxygenation prolongs time to desaturation Preoxygenation with 100% O2 via CPAP at 10cm H2O will give you an extra 1 minute Consider the use of NIV to avoid intubation Dangers - increased risk of gastric insufflation and aspiration Nasal prongs

Drugs Renal blood flow Volume of distribution Liver metabolism

In general Hydrophilic drugs should be dosed on ideal body weight Lipophilic drugs should be based on total body weight

Positioning Head and shoulders should be elevated about the chest such at the external auditory canal is level with the sternal notch Ramped position - multiple folded blankets under head and neck

Intubation Limit the number of conventional laryngoscopy attempts to 3 Consider other advanced airway techniques Video laryngoscopy Bougie Supraglottic devices

Surgical airway Landmarks obscured by excessive soft tissue and a short neck Longer tracheostomy tube with more acute angle Size 6 ETT Under ideal circumstances cricothyroidotomy requires greater than 100 seconds to achieve ventilation

Mechanical ventilation Respiratory mechanics and gas exchange impaired Lung volumes should be based on ideal body weight (often overestimated) PEEP 10 Reverse Trendelenburg