Efficacy of simulated epinephrine-containing epidural test dose after intravenous atropine during isoflurane anesthesia in children

Background and Objectives: A double-blind, randomized study was performed to investigate heart rate (HR) and blood pressure responses to 2 doses of intravenous (IV) epinephrine (0.5 and 0.75 μg/kg) in 61 children, ages 3 months to 12 years. Methods: Anesthesia was maintained with isoflurane (age-adjusted 1 minimal alveolar concentration [MAC]) in oxygen. All patients received IV atropine (10 μg/kg) and 5 minutes later were randomized to receive IV solutions (0.1 mL/kg) containing 1% lidocaine (n = 19, group I) with saline; lidocaine 1% with epinephrine 0.5 μg/kg (n = 21, group II); or lidocaine 1% with epinephrine 0.75 μg/kg (n = 21, group III). HR was recorded at 0, 15, 30, 45, 60, 90 seconds, and 2, 3, 4, and 5 minutes after test-dose injection. Systolic blood pressure (SBP), diastolic blood pressure, and end-tidal carbon dioxide were recorded at steady-state isoflurane anesthesia, after the injection of atropine, and at 45-second intervals after test-dose injections. Results: Median maximum increases in HR were similar in groups II and III at 19 and 22 beats per minute (beats/min), respectively. An HR increase of ≥10 beats/min was observed in 19 of 21 patients who received 0.5 μg/kg epinephrine and 21 of 21 patients receiving 0.75 μg/kg. None of the patients in group I developed HR increases ≥10 beats/min. SBP increased ≥15 mm Hg in 17 of 21 patients in group II and 19 of 21 in group III. No dysrhythmias or T-wave amplitude change was noted. Conclusions: A simulated epidural test dose containing lidocaine 1 mg/kg with epinephrine 0.75 μg/kg, administered IV following atropine, may reliably increase HR to indicate unintentional injection into epidural vessels of children anesthetized with 1 MAC isoflurane. Reg Anesth Pain Med 2000;25:566-572.