DOSE-RESPONSE FOR ATROPINE AND HEART-RATE IN INFANTS AND CHILDREN ANESTHETIZED WITH HALOTHANE AND NITROUS-OXIDE

The dose recommendations for atropine in anesthetized children vary, and the dose-response for heart rate has not been defined. We determined the dose-response for atropine and heart rate in 181 healthy children anesthetized with halothane and nitrous oxide. After induction of anesthesia, atropine in a dose of 5, 10, 20, 30, or 40-mu-g.kg-1 was administered by rapid intravenous infusion to each subject. The effects of atropine on heart rate, heart rhythm, and systolic blood pressure were compared among dosage groups, and a dose-response curve for peak heart rate was constructed. The effects of atropine were compared also between younger and older subjects. For the group of all 181 subjects, atropine increased heart rate in a dose-related manner up to 30-mu-g.kg-1. Fifty percent maximal response corresponded to 9-mu-g.kg-1, and 90% maximal response corresponded to 26-mu-g.kg-1. Some subjects had nonsinus supraventricular rhythms before atropine, but none had nonsinus rhythm after atropine except after the smallest dose, 5-mu-g.kg-1. Systolic blood pressure increased significantly after all doses of atropine except 5-mu-g.kg-1. Subjects < 6 months old had higher control and peak heart rates than did subjects greater-than-or-equal-to 2 yr old, but the older subjects had greater change in heart rate after atropine. For subjects greater-than-or-equal-to 2 yr old, all doses of atropine produced a significant increase in heart rate. The same was true for younger subjects, < 6 months old, except that 5-mu-g.kg-1 did not increase heart rate. Control and response systolic blood pressures were higher for subjects greater-than-or-equal-to 2 yr than for those < 6 months old. Systolic blood pressure did not change after any dose of atropine for subjects < 6 months old, but for subjects greater-than-or-equal-to 2 yr systolic blood pressure increased after doses of atropine 10-mu-g.kg-1 or greater. Atropine in doses greater-than-or-equal-to 10-mu-g.kg-1 increased heart rate and systolic blood pressure and promoted sinus rhythm in children anesthetized with halothane and nitrous oxide. For infants < 6 months old, systolic blood pressure did not change significantly after atropine.