Thiopentone and etomidate concentrations in maternal and umbilical plasma, and in colostrum

Abstract

We have measured concentrations of etomidate and thiopentone in maternal plasma, umbilical venous plasma and colostrum after induction of anaesthesia in 40 patients undergoing Caesarean section. Mean plasma etomidate concentration declined rapidly (1242.0 ng ml-1 at 5 min, 434.0 ng mt1 at 15 min, 64.2 ng ml-1 at 30 min, 7.0 ng ml-1 at 60 min and undetectable 2 h after the injection). Mean plasma concentrations of thiopentone declined more slowly (6.09 μg ml-1 at 5 min, 2.64 μg ml-1 at 2 h, 1.35 ng ml-1 at 4 h, 0.86 ng ml-1 at 9 h and 0.59 ng ml-1 at 12.h). Mean umbilical venous thiopentone concentration was 4.72 μg ml-1. whereas the thiopentone concentration in the maternal sample at 5 min was 6.09 g ml-1, giving an umbilical.maternal vein ratio of 1:1.3. Mean umbilical etomidate concentration was 51.7 ng ml-1 and the corresponding maternal vein sample (5 min) was 1242.0 ng ml-1 (P < 0.001), giving an umbilical: maternal vein ratio of 1:24. Mean concetrations of thioptone in colostrum were 1.98 μg mt-1 at 30 min, 0.91 g mt1 at 4 h and 0.59 μg ml-1 at 9 h, colostrum .plasma ratios at 4 h and 9 h being 0.67 and 0.68, respectively. Mean concentrations of etomidate in colostrum were 79.2 ng ml-1 at 30 min and 16.3 ng ml-1 at 2 h. being undetectable at 4 h. The colostrum:plasma etomidate concentration ratio was 1.2 at 30 min. We conclude that, although plasma and colostrum concentrations of thiopentone and etomidate declined rapidly, the decrease was faster with etomidate. © 1992 British Journal of Anaesthesia.