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Three Part Question

In [obese adults] what [dose of suxamethonium] gives optimal [intubating conditions]?

Clinical Scenario

An obese forty year old woman is brought in to the resuscitation room following a closed head injury, Her GCS is 6/15 and you need to urgently secure a definitive airway. The anaesthetist is busy so you have to proceed with the RSI alone and while drawing up the drugs the Nurse asks you what dose of Suxamethonium you would like. Her husband says she weighs 140kg. You wonder how best to calculate the dose of Suxamethonium to give optimal intubation conditions with shortest time to return of breathing should a failed intubation and ventilation scenario develop.

Search Strategy

Medline 1966 to November week 1 2007 using Dialog Datastar Interface.
[ exp obesity-morbid OR exp obesity OR obese.mp OR obesity.mp ] AND [ exp succinylcholine OR exp neuromuscular depolarising agents OR succinylcholine.mp OR suxamethonium.mp ] AND [ exp intubation.intratracheal OR RSI.mp OR rapid sequence induction.mp OR rapid sequence intubation.mp OR intubation.mp ] Limit to Human and English Language.

Search Outcome

Altogether 13 papers were found of which 1 presented the best evidence.

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Lemmens et al, 2006, USA	45 morbidly obese adults scheduled for gastric bypass surgery	Randomised Double Blind Comparing Succinylcholine 1mg/kg ideal body weight, 1mg/kg lean body weight, 1 mg/kg total body weight	Endotracheal Intubating Conditions	Significant improvement with 1mg/kg actual body weight p < 0.05.	Small number of patients Elective Surgery rather than Emergency Department patients

Comment(s)

After complete denitrogenation, the haemoglobin of an apnoeic morbidly obese adult will desaturate to hypoxaemic levels in <3-4 min. The recovery to 50% twitch height is thought to be time to functional recovery with regard to haemoglobin desaturation risk. In the smallest dose Suxamethonium group, 1mg/kg Ideal Body Weight, this did not occur for 5min, therefore this dose will provide less than ideal intubation conditions without protecting the morbidly obese patient from hypoxia if difficulty is experienced with intubation and ventilation.

Clinical Bottom Line

In obese adult patients a Suxamthonium dose of 1mg/kg Total Body Weight gives optimal intubating conditions.

References

1. Lemmens HJ, Brodsky JB. The Dose of Succinylcholine in Morbid Obesity Anesthesia and Analgesia 2006;102:438-42