Uptake of Enflurane and Isoflurane as Supplement during General Anesthesia for Cesarean Section and Maternal Awareness

Chang, Hae Won; Baik, Hee Jung; Kim, Jong Hak

Abstract

BACKGROUND: Using a semiclosed circle system, general anesthesia for cesarean section was maintained with either 2/3 MAC enflurane or isoflurane in combination with O2: N2O (2 L/min: 2 L/min).
METHODS
We studied the rate of uptake of inhalation agents of pregnant women by measuring inspired concentration and end-tidal concentration of enflurane and isoflurane and we measured the differences in maternal awareness in two groups. The 40 patients presented for elective cesarean section under general anesthesia were randomly assigned to receive either 1.0% enflurane or 0.8% isoflurane with O2: N2O (2 L/min: 2 L/min) for maintenance before delivery using a semiclosed circle system. All patients received thiopental 4 mg/Kg (maximum 250 mg) and succinylcholine 100 mg for induction and were intubated and ventilated with a tidal volume of 10 ml/kg at a rate of 10 breaths/min. After intubation, FI (fractonal inspired concentration) and FE (fractional end tidal concentration) were analyzed by gas monitor (Sirecust 734G, Siemens, Germany) every minute. Intraoperative hemodynamic variables were recorded. Maternal awareness was monitored by the isolated forearm technique.
RESULTS
FI/FINF (fractional inflow concentration) and FE/FINF for the inhalation agents were significantly higher for isoflurane than for enflurane throughout the study after 2 minutes (P < 0.05). The incidence of maternal awareness signaled by both 'spontaneous movement' and 'followed commands' was high and there were no significant differences in the two groups. No patient in our study showed any recollection.
CONCLUSION
We concluded that the rate of uptake of isoflurane was more rapid than that of enflurane but the incidence of maternal awareness was high and there were no significant differences in the two groups.