Lipid emulsions for local anaesthetic toxicity


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The recent interest in the use of uncommonly used lipid suspensions in patients with profound local anaesthetic toxicity prompted me to investigate whether a more readily available lipid emulsion (2, 6-diisopropylphenol, propofol) would be an acceptable alternative. The editorial by Picard and Meek [1] states that ‘propofol is not a suitable alternative because to give a sufficient dose of its carrier lipid, an overdose of propofol would be necessary’, though, unfortunately, they do not support this with references. The recent report by Litz et al. [2] demonstrated that a bolus of 100 ml of Intralipid 20% followed by an infusion in a patient with local anaesthetic-induced asystole restored cardiac output. Other authors have suggested similar dosing regimens [3, 4]. Propofol (Diprivan®, AstraZeneca, Macclesfield, UK) is similar to Intralipid® 10% with regards to its lipid chemistry [5]. If it is assumed that 1% Diprivan® is similar to Intralipid® 10%, then it is easy to calculate that a patient in cardiac arrest secondary to local anaesthetic toxicity, who has not responded to conventional therapy, would need a bolus dose of around 200 ml of propofol to match the amount of Intralipid®, which appears to be effective in resuscitating these patients. This equates to a bolus dose of 2000 mg, or about 30−1 for a 70-kg patient; the recommended induction dose using propofol is 1.5–2.5−1. This is a large dose of a drug whose main side-effects are vasodilation and bradycardia, but these patients will already have supra-normal levels of adrenaline, which will have been administered as part of the ALS algorithm. The rapid distribution, and subsequent metabolism and excretion of propofol suggest the side-effects should not be overly prolonged, and its anticonvulsant properties may be beneficial.

I wonder how long it will be before a case report is published which shows that propofol was used successfully in a patient with refractory cardiac arrest following local anaesthetic toxicity because Intralipid wasn't available?