Thiopentone sensitivity in young and elderly women.

Induction and maintenance doses of thiopentone were smaller in eight elderly women than in eight younger women. Mean venous anaesthetic concentrations were 34% less (P = 0.02) in the elderly. For each patient an "expected maintenance dose" was calculated from serum clearance and the area under the curve during the anaesthesia. In the elderly the average expected dose was equal to the dose given, but in the younger patients the dose given was greater than the expected (P less than 0.02). In younger women, but not in the elderly, a high cardiac output was accompanied by the need for a relatively high maintenance dose if a certain serum concentration was to be maintained. Cardiac output was equally reduced in both patient groups (30-40%). After induction the heart rate was reduced in the elderly during the entire period of anaesthesia and always more than in the younger. No correlation was found between serum concentration of thiopentone and haemodynamic effects.