Background and objective: An estimated 150 million people worldwide use cannabis. The effect of cannabis on anaesthetic requirements in humans does not appear to have been studied.
Methods: In this prospective, randomized, single-blinded study, 30 male patients using cannabis more than once per week (group C) and 30 nonusers (group NC), aged 18–50 years, were induced with propofol 1.5, 2, 2.5, 3 or 3.5 mg kg−1. Additional doses were given when required. The primary outcome was the 50% effective dose of propofol and successful induction was determined by loss of consciousness with a bispectral index value of less than 60 and satisfactory insertion of a laryngeal mask. Propofol requirements to achieve these outcomes were recorded.
Results: The dose required to achieve the target bispectral index value was not significantly higher in group C, but group C required a significantly higher propofol dose to achieve laryngeal mask insertion (314.0 ± 109.3 vs. 263.2 ± 69.5 mg, P < 0.04). The estimated effective propofol induction dose in 50–95% of patients did not significantly differ between groups.
Conclusion: We conclude that cannabis use increases the propofol dose required for satisfactory clinical induction when inserting a laryngeal mask.
aDepartment of Anaesthesia and Intensive Care, Lund University Hospital, Lund, Sweden
bPharmacology Unit, School of Medicine and Pharmacology, University of Western Australia
cDepartment of Anaesthesia and Pain Medicine, Royal Perth Hospital, Australia
dBiostatistician Independent Statistical Consultant, Perth, Australia
Accepted 16 June, 2008
Correspondence to Per Flisberg, MD, PhD, Department of Anaesthesia and Intensive Care, Lund University Hospital, Lund, Sweden Tel: +46 46 17 19 49; fax: +46 46 17 60 50; e-mail: firstname.lastname@example.org