Simulation of an Epidural Test Dose with Intravenous Isoproterenol in Awake and in Halothane-anesthetized Children

Abstract

Background An epidural test dose containing epinephrine does not reliably produce hemodynamic responses in children under halothane anesthesia. 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 before and during anesthesia with 1.2 minimum alveolar concentration halothane. A bolus containing 0.25 mg/ kg bupivacaine and 0.05 microgram/kg, 0.075 microgram/kg, or 0.1 microgram/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, all patients showed a positive test response after isoproterenol injection (heart rate increase > or = 20 beats/min). During anesthesia, 79% of patients receiving 0.05 microgram/kg, 89% of patients receiving 0.075 microgram/kg, and 100% of patients receiving 0.1 microgram/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 occurred in only one patient under halothane anesthesia receiving 0.075 microgram/kg isoproterenol. Conclusion Isoproterenol at a dose of 0.1 microgram/kg is a sensitive indicator for intravascular injection of a test dose in children anesthetized with halothane and nitrous oxide. Isoproterenol at a dose of 0.05 microgram/kg approximates a minimal effective dose in awake children and in infants. After detailed studies on neural toxicity, isoproterenol could be of value as an epidural test agent in children.