Simulation of an epidural test dose with intravenous epinephrine in sevoflurane-anesthetized children.

Abstract

An epidural test dose containing small doses of epinephrine does not produce a reliable increase in heart rate (HR) in children under halothane anesthesia. Because sevoflurane is increasingly used in clinical practice, we designed the present study to determine the hemodynamic responses to, and efficacy of, a simulated IV test dose containing a small dose of epinephrine in sevoflurane-anesthetized children. Sixty ASA physical status I infants and children (4.1 +/- 2.5 yr) undergoing elective minor surgeries were studied during 1.0 minimum alveolar anesthetic concentration of sevoflurane and 60% nitrous oxide in oxygen. The patients were randomly assigned to receive either saline (n = 15), a test dose consisting of 1% lidocaine (0.1 mL/kg) with 1:200,000 epinephrine (0.5 microg/kg, n = 15), atropine 0.01 mg/kg followed 5 min later by saline (n = 15), or atropine followed by the test dose (n = 15) via a peripheral vein to simulate intravascular injection of the epidural test dose. HR and systolic blood pressure were recorded every 15 and 30 s, respectively. The test dose increased the HR from 15 to 60 s and from 15 to 90 s without and with atropine, respectively. Mean maximum increases in HR were similar with and without atropine (21 +/- 8 and 22 +/- 6 bpm, respectively). Of 15 children, 7 and 5 developed HR changes < 20 bpm after the test dose with and without atropine, respectively, whereas all children who received saline had an increase in HR < 20 bpm. No dysrhythmia occurred during the study. Our results indicate that an epidural test dose containing epinephrine is unreliable based on the conventional HR criterion (positive if > or = 20 bpm increase), but reliable on the modified HR criterion (positive if > or = 10 bpm increase) in children anesthetized with sevoflurane. I.v. atropine before the test dose injection did not improve the efficacy based on the conventional HR criterion. Because test doses of epinephrine-containing solution are used to determine whether an epidural catheter is intravascular, it is important to define the optimal test dose under sevoflurane anesthesia. We found that during sevoflurane anesthesia in children, a heart rate increase > or = 10 bpm and a systolic blood pressure increase > or = 15 mm Hg, when preceded by atropine, may be reliable indicators for detecting intravascular injection.