Pharmacokinetics of thiopental in caesarian section.

Anaesthesia for planned caesarian section in nine women was induced with an i.v. thiopental injection. The injection was stopped when the ciliary reflex disappeared. 250-300 mg was given over 60-85 seconds. The concentration of thiopental in peripheral venous blood 20 s after the disappearance of the ciliary reflex varied from 4.3 to 33.7 micrograms/ml. The simultaneously obtained concentrations at delivery (11-25 min after the start of the induction) were 1.7-6.0 micrograms/ml in venous blood from the mothers and 1.3-5.5 micrograms/ml in cord vein blood. In two of the newborns, the Apgar scores were 8 and 9, in the other seven it was 10. The baby with Apgar score 8 was delivered after 25 min and had a concentration in cord vein blood of 3.5 micrograms/ml. The decline in the concentration of thiopental in the venous blood of the mothers was described by a three-compartment open model. The terminal half-life was relatively short, between 91 and 595 min. The blood levels of thiopental in the newborns were followed for 22-33 h. The terminal half-lives in the babies ranged from 616 to 2560 min.