ORAL CLONIDINE BLUNTS THE HEMODYNAMIC-RESPONSES TO BRIEF BUT NOT PROLONGED LARYNGOSCOPY

Study Objective: To determine whether a 300 mug dose of oral clonidine given 90 minutes prior to laryngoscopy and intubation provides hemodynamic protection from the stress of a brief (15-second) and/or a prolonged (45-second) laryngoscopy. Design: Randomized, double-blind, placebo-controlled study. Setting: Inpatients and outpatients scheduled for general anesthesia with intubation at a university-affiliated medical center. Patients: Forty patients who gave informed, written consent to receive either an oral placebo or clonidine 5 mug/kg (up to a maximum dose of 300 mug) 90 minutes prior to induction of anesthesia and to undergo either brief or prolonged laryngoscopy prior to intubation. Interventions: The patients underwent a standardized induction sequence that included d-tubocurarine 3 mg, thiopental sodium 5 mg/kg, and succinylcholine 1.5 mg/kg. The four treatment groups (each n = 10) included (1) placebo with 15-second laryngoscopy, (2) placebo with 45-second laryngoscopy, (3) clonindine with 15-second laryngoscopy, and (4) clonidine with 45-second laryngoscopy. Heart rate (HR), systolic blood pressure (SBP), and diastolic blood pressure (DBP) were mechanically obtained and recorded at 1-minute intervals for 12 minutes. Measurements and Main Results: There were no differences between groups in the premedication hemodynamic measurements. Within each group, maximal hemodynamic variables increased significantly over the corresponding baseline values for that group. In the 15-second, but not the 45-second, laryngoscopy, clonidine successfully blunted the maximum SBP and DBP obtained when compared with the corresponding control group. In both the 15- and 45-second clonidine groups, maximum HR was significantly lower than in the corresponding placebo groups. Conclusions: Oral clonidine, when used as a preoperative medication, affords hemodynamic protection to patients undergoing a 15-second laryngoscopy. However, the stress of a 45-second laryngoscopy may be too great or the 300 mug dose of clonidine too low to provide hemodynamic protection for patients in this group.