Oral clonidine blunts the hemodynamic responses to brief but not prolonged laryngoscopy

Abstract

Study objective: To determine whether a 300 micrograms 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 micrograms/kg (up to a maximum dose of 300 micrograms) 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) clonidine 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 micrograms dose of clonidine too low to provide hemodynamic protection for patients in this group.