[The effects of premedication on induction doses of propofol and hemodynamic responses during induction]

We chose five sedatives for premedication and investigated the effect of these drugs on the induction doses of propofol. One hundred patients were allocated into one of five groups of 20. These groups consisted of control group (C) given only atropine 0.5 mg i.m.; CL group (plus clonidine 0.15 mg orally); H group (plus hydroxyzine 25 mg i.m.); M group (plus midazolam 3 mg i.m.) and D group (plus diazepam 10 mg orally). The induction dose was measured using loss of count technique. Arterial pressure and heart rate were measured, before and after propofol induction as well as after intubation. We also calculated rate pressure products (RPP) at each point. The induction doses were significantly lower in M-group than those in C-group. On the other hand, in hemodynamic responses, RPP was unchanged in any groups after propofol induction and after the intubation. Both propofol and midazolam have been known to have a depressive effect on the central nervous system via GABA-A receptor-mediated inhibition, although the exact receptor for propofol is unknown. We thought, therefore, that when the interaction occurred, both midazolam and propofol had the same effect on the GABA-A receptor and increased chloride ion flux through the channels. Hydroxyzine and clonidine, however, do not share a common receptor or exert effect on the GABA-A receptor. We consider that this was one of the reasons why induction doses of both H and CL group could not decrease significantly. We concluded that midazolam 3 mg decreased propofol induction dose significantly. Both midazolam 3 mg and clonidine 0.15 mg decreased RPP before induction and hemodynamic responses to induction and intubation were stable.