SIMULATION OF AN EPIDURAL TEST DOSE WITH INTRAVENOUS ISOPROTERENOL INAWAKE AND IN HALOTHANE-ANESTHETIZED CHILDREN

Background: An epidural test dose containing epinephrine does not reli ably produce hemodynamic responses in children under halothane anesthe sia. The purpose of this study was to determine hemodynamic responses to intravenous isoproterenol In both awake and halothane-anesthetized children. Methods: After obtaining institutional review board approval and parental informed consent, 72 ASA physical status 1 or 2 children (2.8 +/- 1.7 yr) undergoing elective minor surgery were studied befor e and during anesthesia with 1.2 minimum alveolar concentration haloth ane. A bolus containing 0.25 mg/kg bupivacaine and 0.05 mu g/kg, 0.075 mu g/kg, or 0.1 mu g/kg isoproterenol, or bupivacaine and saline was injected via a peripheral arm vein to simulate intravascular injection of an epidural test dose. Results: Before induction of anesthesia, al l patients showed a positive test response after isoproterenol injecti on (heart rate increase greater than or equal to 20 beats/min). During anesthesia, 79% of patients receiving 0.05 mu g/kg, 89% of patients r eceiving 0.075 mu g/kg, and 100% of patients receiving 0.1 mu g/kg met the criterion of a positive test response. Among each treatment group , all infants showed a positive test response. Blood pressure did not differ among the groups at any time. Transient benign dysrhythmias occ urred in only one patient under halothane anesthesia receiving 0.075 m u g/kg isoproterenol.Conclusion: Isoproterenol at a dose of 0.1 mu g/k g is a sensitive indicator for intravascular injection of a test dose in children anesthetized with halothane and nitrous oxide. Isoproteren ol at a dose of 0.05 mu g/kg approximates a minimal effective dose in awake children and in infants. After detailed studies on neural toxici ty, isoproterenol could be of value as an epidural test agent in child ren.