Effects of premedication on dose requirements for propofol: comparison of clonidine and hydroxyzine.

The influence of a single dose of clonidine (5 micrograms kg-1) or hydroxyzine (1 mg kg-1) on intraoperative propofol requirements was determined in 28 male patients (ASA I) undergoing elective orthopaedic surgery. Patients were randomly allocated to receive either clonidine or hydroxyzine orally 2 h before induction of anaesthesia. After a loading dose of propofol (2.5 mg kg-1), mivacurium (0.2 mg kg-1) and alfentanil (15 micrograms kg-1), anaesthesia was maintained with a standardized propofol infusion supplemented with nitrous oxide (66%) in oxygen. During surgery, additional propofol boluses (1 mg kg-1) were administered when heart rate or mean arterial pressure increased by more than 10% compared with preinduction values. The clonidine group demonstrated a 14.5% decrease in total propofol requirements (P < 0.05) and a 52.2% reduction in additional propofol boluses (P < 0.02) in comparison with the hydroxyzine group. intraoperative heart rate and mean arterial pressure were significantly lower in the clonidine group but no patients needed treatment with ephedrine for hypotension or bradycardia. Recovery of psychomotor function and discharge from the recovery room were not delayed in the clonidine group. This study indicates that 5 micrograms kg-1 clonidine given as premedication in ASA I patients reduces intraoperative propofol requirements in comparison with 1 mg kg-1 hydroxyzine without inducing adverse effects on recovery or haemodynamic stability.