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

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 ml-1 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 micrograms ml-1 at 5 min, 2.64 micrograms ml-1 at 2 h, 1.35 micrograms ml-1 at 4 h, 0.86 microgram ml-1 at 9 h and 0.59 micrograms ml-1 at 12 h). Mean umbilical venous thiopentone concentration was 4.72 micrograms ml-1, whereas the thiopentone concentration in the maternal sample at 5 min was 6.09 micrograms 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 concentrations of thiopentone in colostrum were 1.98 micrograms ml-1 at 30 min, 0.91 microgram ml-1 at 4 h and 0.59 microgram 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 79.3 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.(ABSTRACT TRUNCATED AT 250 WORDS)