Gender differences between predicted and measured propofol C(P50) for loss of consciousness

To investigate gender differences in the effective dose of 50% for loss of consciousness (C(P50LOC)) for propofol using Diprifusor, the most commonly used target-controlled infusion system.

Prospective, randomized, comparative study.

University-affiliated hospital.

50 ASA physical status I and II patients, aged 20 to 50 years, scheduled for minor surgery.

Patients were randomized into two groups of 25 patients each. A target-controlled infusion of propofol (Diprifusor) was maintained at a predetermined target concentration. After a 10-minute steady state, blinded investigators evaluated patients' consciousness using verbal commands. The propofol test concentration was predetermined using a modified version of Dixon's up-and-down method (starting at 2.5 mug/mL; step size of 0.1 microg/mL).

Predicted and measured C(P50LOC) values and bispectral index (BIS) were obtained by averaging the crossover midpoint (ie, consciousness to unconsciousness). Those values were analyzed by unpaired t test: P < 0.05 was considered significant.

The predicted C(P50LOC) for men was 2.14 +/- 0.10 microg/mL, which was lower than that for women, 2.55 +/- 0.11 microg/mL (P < 0.0001). No significant difference was found for measured C(P50LOC) in men (2.37 +/- 0.41 microg/mL) and in women (2.30 +/- 0.28 microg/mL) or for BIS measurements.

Predicted C(P50LOC) by Diprifusor for men tended to be underestimated; that for women tended to be overestimated. Our data support a review of Diprifusor (Astra Zeneca, Osaka, Japan) pharmacokinetic parameters to avoid awareness during operation, particularly for women.