Early pregnancy does not reduce the C-50 of propofol for loss of consciousness

Requirements for inhaled anesthetics decrease during pregnancy. There are n o published data, however, regarding propofol requirements in these patient s. Because propofol is often used for induction of general anesthesia when surgery is necessary in early pregnancy, we investigated whether early preg nancy reduces the requirement of propofol for loss of consciousness using a computer-assisted target-controlled infusion (TCI). Propofol was administe red using TO to provide stable concentrations and to allow equilibration be tween blood and effect-site (central compartment) concentrations. Randomly selected target concentrations of propofol (1.5-4.5 mug/mL) were administer ed to both pregnant women (n = 36) who were scheduled for pregnancy termina tion and nonpregnant women (n = 36) who were scheduled for elective orthope dic or otorhinolaryngologic surgery. The median gestation of the pregnant w omen was 8 wk (range, 6-12 wk). Venous blood samples for analysis of the se rum propofol concentration were taken at 3 min and 8 min after equilibratio n of the propofol concentration. After a 10-min equilibration period of the predetermined propofol blood concentration, a verbal command to open their eyes was given to the patients twice, accompanied by rubbing of their shou lders. Serum propofol concentrations at which 50% of the patients did not r espond to verbal commands (C-50 for loss of consciousness) were determined by logistic regression. There was no significant difference in C-50 +/- SE of propofol for loss of consciousness between the Nonpregnant (2.1 +/- 0.2 mug/mL) and Pregnant (2.0 +/- 0.2 mug/mL) groups. These results indicate th at early pregnancy does not decrease the concentration of propofol required for loss of consciousness.