Dose Response of Intravenous Thiopental for Induction of General Anesthesia in Cesarean Section Patients and in Patients with End Stage Renal Disease

Kim, Won Oak; Kil, Hea Keum; Kim, Jong Rae; Park, Kwang Won

Abstract

The dose-response of intravenous thiopental (2.5%) for induction of general anesthesia in cesarean section (C/S) patients and in patients with end stage renal disease(ESRD) was studied at seven doses of 2.0, 3.0, 3.5, 4.0, 4.5, 5.0 and 6.0 mg/kg body weight. Thiopental was injected as an IV bolus into a preexisting IV catheter. Patients were divided into four groups(ESRD-CONTROL, C/S-CONTROL, C/S, and ESRD). Each patient was examined at 60 seconds after injection of thiopental. Presence or absence of verbal command response, lid reflex and trapexius reflex were observed. For each reflex, dose-response curves were analysed using the log probit model to determine ED 50, Ed95 and parallelism. The value of ED50 for verbal command response was lowest in the ESRD patient group (2.2mg/kg) and was similar in the remaining groups(2.5, 2.6mg/kg). The ED50 values for lid and trapezius reflex were lowest in the C/S group(2.9and 4.0mg/kg respectively) and the others had similar values (3.5~3.7mg/kg and 4.7~5.3mg/kg respectively). The ED95 values for trapezius reflex in all patients were distributed between a range of 6.5~9.1mg/kg and this suggests that the usual dose (3~6 mg/kg) is not sufficient to prevent the stress response of tracheal intubation. Also, the results indicate that the dose of thiopental for induction should be reduced because of the increasing sensitivity of the central nervous system with the cesarean section group and the free drug fraction of thiopental in patients with end stage renal disease. Therefore, if a patient with full term pregnancy or renal failure is to be induced with a single injection of thiopental, it is recommended to reduce the rate of injection.