Effects of clonidine on anesthetic drug requirements and hemodynamic response during aortic surgery.

The authors studied in a double-blind placebo-controlled study the effects of oral preoperative administration of 5 micrograms/kg clonidine upon the alfentanil and droperidol requirements, hemodynamic lability, distribution of the values of heart rate and blood pressure, and plasma noradrenaline levels, in two groups of ten normotensive patients undergoing infrarenal aortic surgery. The amounts of alfentanil supplementing a standardized continuous infusion, injected to maintain hemodynamic stability, were statistically identical between the groups (P = 0.23). The amount of droperidol, however, was significantly less (P = 0.004) in the group of patients that received clonidine. The norepinephrine plasma concentrations, during the entire procedure, were lower (P = 0.001) in the clonidine group. The variability of the heart rate, systolic (SBP) and diastolic (DBP) blood pressure recorded every 5 s, and assessed by the calculation of the coefficients of variation for each patient, showed no difference between the clonidine and the placebo group. However, when the values recorded were compared to the preoperative baseline values, and divided into three categories (baseline +/- 20%--greater than 20% decrease vs. baseline--greater than 20% increase vs. baseline), the clonidine group showed a higher frequency of low heart rate and fewer episodes of tachycardia. The frequency of SBP hypertension was lower and of SBP hypotension higher in the clonidine group. After induction of anesthesia, but before surgery, there were more episodes of DBP hypotension in the clonidine group, but during dissection and vascular sutures the placebo group experienced more episodes of DBP hypotension, owing probably to the greater amount of droperidol injected. The authors conclude that the preoperative administration of clonidine decreased the need to supplement anesthetic, and modifies the profile of distribution of heart rate and blood pressure.