CLONIDINE PREMEDICATION FOR CRANIOTOMY - EFFECTS ON BLOOD-PRESSURE AND THIOPENTONE DOSAGE

The purpose of this study was to determine whether oral clonidine prem edication improves cardiovascular stability and/or reduces the require ments for drugs used to control systolic blood pressure (SBP) during e lective craniotomies. We performed a double blind randomized trial inv olving 77 normotensive, ASA physical status I or II adults. Clonidine 4 mug/kg or placebo was given as oral premedication. The patient's mea n SBP on the day before surgery was used as the baseline. SBP was cont rolled between the baseline and 30% below it (but not <90 mm Hg). Anes thesia was induced with thiopentone, N2O, and fentanyl; maintenance wa s with N2O. Further doses of thiopentone were administered to control rises in SBP until skin incision. After skin incision trimethaphan (TM P) was used to control the SBP and isoflurane only added if TMP was in sufficient. Isoflurane was discontinued as soon as SBP control allowed . The induction dose of thiopentone was the same in both groups but su bsequent usage for blood pressure control was significantly lower in t he clonidine group. There were no differences in trimethaphan dose, or the incidence and duration of isoflurane use. The clonidine group had lower SBP on arrival in the operating room, preinduction, and postint ubation. There were no differences in mean ''intraoperative'' SBP, the ir coefficients of variation, or recovery room values. Two subgroups w ere analyzed, based on the study groups mean age and baseline SBP. Thr ee-way analysis of variance revealed that the blood pressure effects o f clonidine were almost entirely confined to patients older than 45 ye ars. Baseline SBP had no independent effect. The effects of clonidine found in this study, although statistically significant, seem to us to have only minor clinical importance.