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We conducted a prospective, randomized, double-blind , controlled clinical trial to examine (1) whether plasma catecholamine (CA) concentrations increased in response to tracheal intubation in children, and (2) the effects of clonidine on the CA responses. Sixty children (ASA physical status I) aged 7-13 yr were allocated to one of three groups (n = 20 for each group): diazepam 0.4 x kg(-1) (active control), clonidine 2 micrograms x kg(-1), or clonidine 4 micrograms x kg(-1) po. These agents were administered 105 min before induction of anaesthesia followed by oral atropine 0.03 mg x kg(-1) given 60 min before anaesthesia which was induced with thiamylal 5 mg x kg(-1) and tracheal intubation was facilitated with vecuronium 0.2 mg x kg(-1). Laryngoscopy, lasting 30 sec, was attempted two minutes after administration of the induction agents. Serial values for blood pressure, heart rate, and venous plasma CA concentrations were compared among the three groups and with the respective preinduction measurements. Children receiving diazepam or clonidine 2 micrograms x kg(-1) showed remarkable increases in systolic and diastolic blood pressures, heart rate, and plasma CA concentrations in response to tracheal intubation (P &lt; 0.05). The increases were similar for the two regimens. These haemodynamic and CA changes were smaller in children receiving clonidine 4 micrograms x kg(-1) (P &lt; 0.005). The haemodynamic responses were positively correlated with the CA responses. These findings indicate that tracheal intubation following rapid sequence induction of anaesthesia in children provokes a reflex increase in sympathetic activity characterized by increased plasma CA concentrations, and that attenuation of the cardiovascular changes with a high oral dose of clonidine may be due to suppression of the increase in sympathetic activity evoked by the intubation.

Attenuation of the catecholamine response to tracheal intubation with oral clonidine in children