Early Pregnancy Does Not Reduce the C50 of Propofol for Loss of Consciousness

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Requirements for inhaled anesthetics decrease during pregnancy. There are no published data, however, regarding propofol requirements in these patients. Because propofol is often used for induction of general anesthesia when surgery is necessary in early pregnancy, we investigated whether early pregnancy reduces the requirement of propofol for loss of consciousness using a computer-assisted target-controlled infusion (TCI). Propofol was administered using TCI to provide stable concentrations and to allow equilibration between blood and effect-site (central compartment) concentrations. Randomly selected target concentrations of propofol (1.5–4.5 μg/mL) were administered to both pregnant women (n = 36) who were scheduled for pregnancy termination and nonpregnant women (n = 36) who were scheduled for elective orthopedic or otorhinolaryngologic surgery. The median gestation of the pregnant women was 8 wk (range, 6–12 wk). Venous blood samples for analysis of the serum propofol concentration were taken at 3 min and 8 min after equilibration 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 shoulders. Serum propofol concentrations at which 50% of the patients did not respond to verbal commands (C50 for loss of consciousness) were determined by logistic regression. There was no significant difference in C50 ± se of propofol for loss of consciousness between the Nonpregnant (2.1 ± 0.2 μg/mL) and Pregnant (2.0 ± 0.2 μg/mL) groups. These results indicate that early pregnancy does not decrease the concentration of propofol required for loss of consciousness.

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