[The effects of preanesthetic oral clonidine upon heart rate response to intravenous atropine in patients during general anesthesia].
In awake subjects the positive chronotropic effect of intravenously administered atropine 10 micrograms.kg-1 has been demonstrated to be blunted by preanesthetic medication of oral clonidine 5 micrograms.kg-1. The aim of the present study is to investigate whether general anesthesia could alter the clonidine-induced attenuation of positive chronotropic effect by atropine. Thirty-two patients were randomly assigned to one of the two groups; patients of the clonidine group received oral clonidine 5 micrograms.kg-1 (n = 12), whereas those of the control group received no clonidine. General anesthesia was induced with intravenous thiamylal 4-5 mg.kg-1, and was maintained with enflurane and nitrous oxide in oxygen after endotracheal intubation. Following the stable circulatory period of 10 min, hemodynamic measurements were made at 1 min intervals for 10 min after atropine 10 micrograms.kg-1 was administered intravenously as a bolus in both groups. A significant attenuation in heart rate response to intravenous atropine 10 micrograms.kg-1 was observed in patients receiving clonidine 5 micrograms.kg-1, as compared with that in the control group (P less than 0.01); maximal increases in heart rate were 15 +/- 8 and 22 +/- 6 beats.min-1 (mean +/- SD) in the clonidine and control groups, respectively. It is concluded that clonidine 5 micrograms.kg-1 blunts the heart rate response to intravenous atropine 10 micrograms.kg-1 in patients anesthetized with enflurane and nitrous oxide in oxygen.
Nishikawa
T
T
Department of Anesthesiology, University of Tsukuba.
Kimura
T
T
Ikemura
A
A
Iwai
R
R
Sakaguchi
M
M
Goyagi
T
T
D000284:Administration, Oral; D000293:Adolescent; D000328:Adult; D000768:Anesthesia, General; D001285:Atropine / Q000008:administration & dosage / Q000037:antagonists & inhibitors*; D003000:Clonidine / Q000008:administration & dosage / Q000494:pharmacology*; D006339:Heart Rate / Q000187:drug effects*; D006801:Humans; D007275:Injections, Intravenous; D008875:Middle Aged
D001285:Atropine; D003000:Clonidine