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OBSTETRIC ANESTHESIA

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

Hideyuki Higuchi, MD^*, Yushi Adachi, MD, Shinya Arimura, MD^*, Masuyuki Kanno, MD^*, and Tetsuo Satoh, MD

*Department of Anesthesia, Self Defense Force Central Hospital, Tokyo; and Department of Anesthesiology, National Defense Medical College, Saitama, Japan

Address correspondence to Hideyuki Higuchi, MD, Department of Anesthesia, Self Defense Force Hanshin Hospital, 4-1-50 Kushiro, Kawanishi, Hyogo 666-0024, Japan. Address e-mail to higu-chi@ ka2.so-net.ne.jp.

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.

IMPLICATIONS: The C₅₀ of propofol for loss of consciousness in early pregnancy did not differ from that in nonpregnant women, indicating that there is no need to decrease the propofol concentration for loss of consciousness when inducing general anesthesia for termination of pregnancy.

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