Morbidly obese patients can pose numerous challenges when it comes to airway management. Morbid obesity can make vascular access more difficult and you need good vascular access prior to any attempts at safe airway management. In addition, morbid obesity can cause an anatomically difficult airway and decreases the safe apnea time until desaturation occurs and increases the recovery time once the patient does desaturate. Finally, the medications frequently used for intubation and ongoing sedation and analgesia must be dosed differently compared with non-obese patients.
First of all, the morbidly obese patient frequently has a short neck with a wide circumference causing a short thyromental distance. This can lead to a more anterior larynx causing a Cormack-Lehane grade III-IV laryngoscopic view during direct laryngoscopy. Second, many morbidly obese patients have a very wide chest circumference that can impair the operator’s ability to advance a laryngoscope into the mouth with the patient in supine position. The reason for this difficulty is because the anterior chest wall protrudes out and can block the laryngoscope shaft from getting to the proper anterior position to allow the blade at the proper angle into the patient’s mouth. Understanding these challenges, the ideal position for airway management of a morbidly obese patient is the “ramp position” and reverse Trendelenberg position. This combination optimizes the chance of a good laryngoscopic view and prolongs the safe apnea time (duration until desaturation <90% occurs) and decreases the recovery time should desaturation occur. Boyce et al. determined that the safe apnea time for intubations of morbidly obese patients (BMI>40) in the supine position averaged 123 seconds whereas the safe apnea time was nearly 1 minute longer at 178 seconds in the reverse Trendelenberg position. Similarly, the recovery time after desaturation was much less in the reverse Trendelenberg position (80 seconds) vs 206 seconds in the supine position. Additionally, video laryngoscopy provides a higher first pass success rate compared with direct laryngoscopy for intubations performed in the emergency department or in the ICU.
In addition to the challenges of intubating a morbidly obese patient, the medications used for airway management and ongoing analgesia and sedation during mechanical ventilation are often dosed differently than their non-obese counterparts. Some medications are dosed based on actual body weight, some are dosed based on ideal body weight and some based on lean body weight (or adjusted body weight) which is roughly 40% higher than ideal body weight.
Medications dosed based on actual body weight: succinylcholine, maintenance propofol, midazolam and lorazepam IV boluses
Medications dosed based on ideal body weight: rocuronium, vecuronium, cisatracurium, morphine, ketamine, midazolam infusions
Medications dosed based on adjusted body weight: fentanyl, induction propofol, etomidate and dexmedetomidine
These nuances of difficult airway management are some of the procedural skills that you will learn at the HPC Hospitalist and Emergency Procedures course that has trained over 6,000+ clinicians to become airway management experts with proficiency in endotracheal intubation, laryngeal mask airway placement, King tube placement, stylet-guided intubations, Glidescope intubations, cricothyroidotomy and fiberoptic intubations.
REFERENCES:
Kristensen MS. Airway management and morbid obesity. Eur J Anaesthesiol. 2010; 27(11): 923.