Hypnotic effect of i.v. propofol is enhanced by i.m. administration of either lignocaine or bupivacaine

We have compared the hypnotic requirements for i.v. propofol when combined with i.m. lignocaine or bupivacaine. Ninety women (ASA I, II) undergoing minor gynaecological surgery were allocated randomly to one of nine groups of 10 patients to receive propofol combined with i.m. lignocaine, bupivacaine or saline, respectively. Propofol was administered in bolus doses of 0.2 mg kg^-1 every 30 s until loss of response to verbal command was achieved, Lignocaine and bupivacaine significantly enhanced the hypnotic effect of propofol in a dose-dependent manner. The maximum doses tested (lignocaine 3.0 mg kg^-1 and bupivacaine 1.0 mg kg^-1) reduced the hypnotic dose of propofol by 34.4% and 39.6%, respectively. We conclude that if lignocaine or bupivacaine is injected into soft tissue before induction of anaesthesia by propofol, the i.v. dose of the latter should be modified accordingly.