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