Anaesthesia for the morbidly obese patient

Last Updated on by FRCEM Intermediate

Pathophysiologic Considerations in Obesity

  1. The decreased respiratory reserve is secondary to diminished total lung capacity and functional residual capacity. The decreased reserve compromises an obese patient’s ability to tolerate respiratory insults such as pneumonia
  2. Increased airway pressures are a result of increased airway resistance (heavier chest walls, increased abdominal girth, atelectatic lung bases). The increased pressures lead to:
    1. Smaller oxygen reserves at baseline
    2. Increased work of breathing
    3. Shorter time to desaturation during induction and a shorter Safe Apnea Time
  3. Higher incidence of hypoxemia and hypercapnia at baseline
  4. Higher risk of aspiration pneumonitis
  5. More difficult to ventilate with BMV

 

Ventilation and Induction in Obese patient

GET HELP: anticipate challenging airway.an experienced physician should be the first to attempt intubation. Consider calling your colleagues from anesthesia, ICU or ENT.

RAMP: 30 degree head up position, try to achieve ear-to-sternal-notch Position with towels or commercially available products. then position the patient in reverse Trendelenburg to take the weight of the pans off the chest.

APNOEIC OXYGENATION: Use nasal cannulas at 15L underneath the facemask or bag-valve-mask to maintain diffusion of oxygen and help blow open the oropharynx

MINIMAL DRUGS: Know the correct dosing scalars for induction agents and muscular relaxants

PRE-OXYGENATE WITH NIV: This will help improve Safe Apnea Time in patients with decreased respiratory reserve.

PARALYSIS – Use of appropriate dose is sedation and paralytic. Once paralyzed you may encounter a “can’t oxygenate, can’t ventilate” situation.

The PLAN FOR FAILURE:

  • Mallampati and large neck circumference = difficult laryngoscopy /intubation.
  • Facemask ventilation is frequently problematic –needs two hands ventilation and airways.
  • Avoid laryngeal and supraglottic devices, endotracheal tubes should be the default airway

A summary of the available strategies for reducing aspiration risk

Reducing gastric volume Preoperative fasting
Nasogastric aspiration
Prokinetic premedication
Avoidance of general anaesthetic Regional anaesthesia
Reducing pH of gastric contents Antacids
H2 histamine antagonists
Proton pump inhibitors
Airway protection Tracheal intubation
Second-generation supra-glottic airway devices
Prevent regurgitation Cricoid pressure
Rapid sequence induction
Extubation Awake after return of airway reflexes
Position (lateral, head down or upright)

Read :

Episode 69 Obesity Emergency Management

Apnoeic oxygenation

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