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Mechanism of injection pain with long and long-medium chain triglyceride emulsive propofol

[Le mécanisme de la douleur à l’injection d’une émulsion de propofol et de chaînes longues et mi-longues de triglycérides]

From the Department of Anesthesiology, Central Aizu General Hospital, Aizuwakamatsu, Japan.

Address correspondence to: Dr. Hiroshi Iwama, Department of Anesthesiology, Central Aizu General Hospital, 1-1 Tsurugamachi, Aizuwakamatsu City 965-0011, Japan. Fax: +81-242-24-1529; E-mail: iwama{at}onchikai.jp

Purpose: t has been suggested that long-medium chain triglyceride (LCT/MCT) emulsive propofol causes less injection pain than long chain triglyceride (LCT) emulsive propofol because of the decreased propofol concentration in the aqueous phase. Alternatively, LCT propofol generates bradykinin causing the injection pain and activates complement, but these effects when using LCT/MCT propofol have not been examined. To identify the mechanism for reduced pain with LCT/MCT propofol, injection pain, bradykinin generation and complement activation with use of both propofol products were compared.

Methods: Two hundred adult patients randomly allocated to two groups were given 1.5 mg·kg^–1 iv of either LCT propofol or LCT/MCT propofol at a rate of 200 mg·min^–1 in a double-blind manner and were asked to grade pain scores. In another study, bradykinin and activated complement 3 (C3a) concentrations were measured using blood obtained from 13 healthy volunteers mixed with saline, LCT propofol or LCT/MCT propofol.

Results: There was a significant difference in pain scores between groups, showing a lower incidence of injection pain in the LCT/MCT propofol group. The bradykinin concentrations in blood mixed with LCT and LCT/MCT propofol were significantly higher than in blood mixed with saline. The C3a concentrations showed similar results.

Conclusions: LCT/MCT propofol causes less pain on injection compared with LCT propofol. Bradykinin generation and complement activation are similar with both LCT and LCT/MCT propofol. Thus, the reason for less pain on injection with LCT/MCT propofol may be attributed to a decreased concentration of propofol in the aqueous phase.