Aortocaval compression and plasma concentrations of thiopentone at caesarean section

The venous plasma concentration-time profiles of thiopentone were measured simultaneously over the first 30-40 min after induction of anaesthesia, in blood obtained from an arm vein and a vein in the foot, in nine healthy full-term women undergoing Caesarean section. Patients were tilted laterally to the left by from 8 to 18 degrees during the procedure. In all but two of the patients, the profiles from the arm and foot were virtually identical, suggesting that aortocaval compression was absent or insignificant. Therefore, the large intersubject variability in volume of distribution of thiopentone at Caesarean section is unlikely to be the result of aortocaval compression.