Not surprisingly, heavier patients had lower first-pass endotracheal tube success. They also had succinylcholine under-dosed more often. Give yourself the best chance for success and optimize muscle relaxation in obese patients.
Why does this matter?
Your first look with the laryngoscope needs to be your best look. Bad things happen the longer it takes to intubate. A review article in Annals of EM said, "Succinylcholine should be dosed according to total body weight... Nondepolarizing neuromuscular blocking agents such as rocuronium and vecuronium should be dosed according to ideal body weight because of their hydrophilicity." Based on dose finding studies, the authors of this paper suggest that ideal succinylcholine doses should be between 1.5 mg/kg and 2 mg/kg. That means big doses in big people.
Big person = big dose of sux
This was a retrospective review of the association of weight with first pass success in patients intubated in the ED. They found that in patients in the heaviest weight category (>120kg) first pass success was lower than those in the lowest weight group (<80kg): 76% vs 91%. The per kilogram dose of succinylcholine dropped as weight increased, nearly 1.5mg/kg in those under 80kg vs. 1mg/kg in patients >120kg. In fact, 54% of the patients weighing greater than 120kg received less than 1mg/kg of succinylcholine. Rocuronium doses were around 1.4mg/kg regardless of weight. It is not possible to say the lower succinylcholine dose caused lower first pass success, but there is a cautionary message. Give yourself the best chance for success. Poor muscle relaxation makes intubation difficult, as does obesity. You can only control one of those variables.
Effect of patient weight on first pass success and neuromuscular blocking agent dosing for rapid sequence intubation in the emergency department. Emerg Med J. 2017 Nov;34(11):739-743. doi: 10.1136/emermed-2017-206762. Epub 2017 Aug 16.
Peer reviewed by Thomas Davis, MD.