To assess the adequacy of the general anesthesia commonly employed for Cesarean section, we used isolated forearm technique to study 30 parturients (physical status ASA I/II, aged 17–35 yr) scheduled for nonemergent abdominal delivery. Anesthesia was induced with intravenous thiopental (3 mg/kg, 250 mg maximum) and succinylcholine (1.5 mg/kg), and then proceeded with a mixture of 50% N2O, 50% O2, and 0.5%) halothane at a flow of 5 L/min and end-tidal CO2 at 40 mm Hg. Paralysis was maintained with a 0.1% succinylcholine infusion, When eyelash reflex disappeared, patients received taped instruction via headphones at 1-min intervals for 10 min. The tapes instructed patients to flex fingers if they were able to hear, to make a fist or squeeze the investigator's hand if they felt pain, to remember six target words, and to respond with specific physical signals during later interviews. Three sets of tapes assigned at random were used in the study. For signs of inadequate anesthesia, other variables such as eye centering, pupil size, sweating, and lacrimation were concomitantly monitored at the time of induction, laryngoscopy/intubation, and skin incision, and then at I-min intervals for 10 min. Brain activity was also monitored by means of computerized aperiodic analysis of electroencephalogram Lifescan®). Patients were interviewed in the postanesthesia recovery room and again 24 h later. At the time of skin incision, 96.7% of patients (29/30) signaled awareness by flexing fingers, 86.7% (26/30) exhibited lacrimation, and 80% (24/30) made a fist or squeezed the investigator's hand, indicating pain perception. One minute after skin incision, 76.7% (23/30) signaled awareness and 63.3% (19/30) signaled pain. Two minutes after skin incision, 20% (6/30) signaled awareness, 6.7% (2/30) signaled pain, and one patient showed signs of awareness for an additional minute. In postoperative interviews, no patient remembered any intraoperative events or any target word, nor did anyone respond with physical signals requested in the taped instruction. Brain activity monitoring revealed a significant shift of activity edge to the left, with decrement of frequency after induction and during endotracheal intubation in all parturients, an abrupt, marked increase of frequency during skin incision in 83.3% (25/ 30) of mothers, and a marked slowing of frequency after narcotic administration followed by delivery in all of them. We conclude that allowing surgery to begin immediately after endotracheal intubation does not provide adequate anesthesia at the time of skin incision during abdominal delivery.
Address correspondence and reprint requests to Hwa-kou King, M.D., Associate Professor, Department of Anesthesiology, King/ Drew Medical Center, 12021 S. Wilmington Avenue, Los Angeles, CA 90059.
© 1993 International Anesthesia Research Society