Clonidine premedication for craniotomy: effects on blood pressure and thiopentone dosage

The purpose of this study was to determine whether oral clonidine premedication improves cardiovascular stability and/or reduces the requirements for drugs used to control systolic blood pressure (SBP) during elective craniotomies. We performed a double blind randomized trial involving 77 normotensive, ASA physical status I or II adults. Clonidine 4 micrograms/kg or placebo was given as oral premedication. The patient's mean SBP on the day before surgery was used as the baseline. SBP was controlled between the baseline and 30% below it (but not < 90 mm Hg). Anesthesia was induced with thiopentone, N2O, and fentanyl; maintenance was with N2O. Further doses of thiopentone were administered to control rises in SBP until skin incision. After skin incision trimethaphan (TMP) was used to control the SBP and isoflurane only added if TMP was insufficient. Isoflurane was discontinued as soon as SBP control allowed. The induction dose of thiopentone was the same in both groups but subsequent usage for blood pressure control was significantly lower in the 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 postintubation. There were no differences in mean "intraoperative" SBP, their coefficients of variation, or recovery room values. Two subgroups were analyzed, based on the study groups mean age and baseline SBP. Three-way analysis of variance revealed that the blood pressure effects of clonidine were almost entirely confined to patients older than 45 years. Baseline SBP had no independent effect.(ABSTRACT TRUNCATED AT 250 WORDS)