Authors: Morris, J.¹; Acheson, M.²; Reeves, M.³; Myles, P. S.²

Source: BJA: British Journal of Anaesthesia, Volume 95, Number 2, August 2005 , pp. 183-188(6)

Publisher: Oxford University Press

Abstract:

Background. Pre-medication with clonidine reduces the requirement for volatile agents during general anaesthesia. This may also be true for anaesthesia with propofol, but the amount of dose reduction has not been measured. Because clonidine also affects cardiac output and thus regional blood flow it could alter the pharmacokinetics of propofol. This randomized, double-blind placebo-controlled trial aimed to study the effect of clonidine pre-medication on dose requirement for propofol during lower extremity vascular surgery using the bispectral index (BIS) as a measure of anaesthetic depth.

Methods. After oral pre-medication with either clonidine 3 g kg^-1 or placebo, 39 subjects had lower limb vascular surgery using propofol infusion for anaesthesia. Anaesthetic depth was adjusted to a BIS of 45. Predicted plasma propofol concentrations were noted every 30 min from a target-controlled propofol infusion pump and arterial samples were taken at the same time for propofol measurements.

Results. Patients in both groups were anaesthetized to similar depths of anaesthesia as indicated by BIS readings (P=0.44). The groups had comparable mean (95% CI) arterial concentrations of propofol, 4.8 (3.5–6.1) g ml^-1 in the patients given clonidine, and 4.6 (3.4–5.7) g ml^-1 in the patients given placebo (P=0.81). However, the average plasma concentration predicted by the target-controlled infusion was less in the clonidine group [3.2 (2.9–3.5)] than in the group given placebo [3.6 (3.3–3.9)] g ml^-1 (P<0.05).

Conclusions. Pre-medication with clonidine reduces the requirement for propofol, which is a pharmacokinetic effect and not a pharmacodynamic central sedative effect.

Keywords: anaesthetics i.v; propofol; pharmacokinetics; premedication; clonidine

Document Type: Research article

DOI: http://dx.doi.org/10.1093/bja/aei172

Affiliations: 1: Department of Anaesthesia and Pain Management, Royal Melbourne Hospital, Parkville, Victoria, Australia. 2: Department of Anaesthesia and Pain Management, Alfred Hospital, Melbourne, Victoria, Australia. 3: North West Regional Hospital, Burnie, Tasmania, Australia.

Publication date: 2005-08-01

More about this publication?

• Founded in 1923, one year after the first anaesthetic journal was published by the International Anaesthesia Research Society, the British Journal of Anaesthesia remains the oldest and largest independent journal of anaesthesia. It became the journal of The College of Anaesthetists in 1990. The College was granted a Royal Charter in 1992. Although there are educational links between the BJA and the College, the journal retains editorial independence.

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