Oral clonidine premedication does not change efficacy of simulated epidural test dose in sevoflurane-anesthetized children.

BACKGROUND

Caudal epidural anesthesia is often used as an adjunct to general anesthesia and for postoperative pain relief in children. In anesthetized children, epinephrine and isoproterenol are reliable indicators to detect accidental intravascular injection of a test dose. Oral clonidine, a useful premedicant in pediatric anesthesia, modifies hemodynamic responses to sympathomimetics, including catecholamines. The aim of the current study was to determine whether oral clonidine premedication alters the efficacy of a simulated intravascular test dose containing epinephrine or isoproterenol in sevoflurane-anesthetized children.

METHODS

One hundred twenty children (aged 1-7 yr) were randomly divided into six groups; control-saline, control-epinephrine, control-isoproterenol, clonidine-saline, clonidine-epinephrine, and clonidine-isoproterenol. The three clonidine groups received oral clonidine 4 microg/kg [DOSAGE ERROR CORRECTED] as premedication, whereas the three control groups did not receive any premedication. Anesthesia was maintained with sevoflurane at a level of 1.2 minimum alveolar concentration. After hemodynamics were stable, 0.1 ml/kg of 1% lidocaine containing epinephrine 0.5 mg/kg or isoproterenol 75 ng/kg was intravenously given to the two epinephrine or isoproterenol groups, respectively, to simulate intravascular injection of a test dose. The saline groups received saline alone instead of the test dose. Heart rate, blood pressure, and T-wave amplitude of electrocardiogram were recorded before and after administration of study drugs for subsequent analysis.

RESULTS

Test solution containing epinephrine increased heart rate, systolic blood pressure, and T-wave amplitude. Oral clonidine had no effect on elevation of these variables in response to epinephrine. The isoproterenol-containing test dose produced a prominent increase in heart rate and a less pronounced increase in systolic blood pressure and T-wave amplitude. Oral clonidine also failed to modify isoproterenol-induced hemodynamic and T-wave changes. Calculated sensitivity and specificity of epinephrine or isoproterenol were all 100% based on a new heart rate criterion (positive if >/= 10 beats/min) and were unaltered by oral clonidine premedication.

CONCLUSIONS

Epinephrine or isoproterenol is a reliable marker to detect accidental intravascular injection of a test dose with 100% sensitivity and specificity based on a new heart rate criterion in sevoflurane-anesthetized children. These data suggest that oral clonidine premedication does not alter the efficacy of a simulated epidural test dose containing epinephrine or isoproterenol.