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Pathophysiologic Considerations in Obesity
- 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
- Increased airway pressures are a result of increased airway resistance (heavier chest walls, increased abdominal girth, atelectatic lung bases). The increased pressures lead to:
- Smaller oxygen reserves at baseline
- Increased work of breathing
- Shorter time to desaturation during induction and a shorter Safe Apnea Time
- Higher incidence of hypoxemia and hypercapnia at baseline
- Higher risk of aspiration pneumonitis
- 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) |
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