THE EFFICACY OF EPINEPHRINE TEST DOSES DURING SPINAL-ANESTHESIA IN VOLUNTEERS - IMPLICATIONS FOR COMBINED SPINAL-EPIDURAL ANESTHESIA

Epinephrine test doses may be administered during combined spinal-epid ural anesthesia to determine intravascular placement of epidural cathe ters. This study was designed to determine systolic blood pressure (SE P) and heart rate (HR) responses to intravenous injection of epinephri ne (15 mu g) during spinal anesthesia. Twelve volunteers received thre e spinal anesthetics (lidocaine 100 mg, tetracaine 15 mg, and bupivaca ine 15 mg) in a randomized, double blind, cross-over fashion. Epinephr ine was administered prior to spinal anesthesia (control), 30 min afte r injection of spinal anesthesia, and at regression of sensory block t o T-10. SBP was measured with a radial arterial catheter and HR with a n electrocardiogram. Positive responses were defined as peak increase in SBP greater than or equal to 15 mm Hg or HR greater than or equal t o 20 bpm after injection of epinephrine. Compared with control, peak S BP responses decreased by a mean of 12 mm Hg during spinal anesthesia with tetracaine and bupivacaine (P < 0.05). Peak HR responses decrease d by 11 bpm during all three spinal anesthetics (P < 0.05). Incidences of detection of intravenous injection by positive SBP and HR response s ranged from 50% to 100% and were not significantly affected by spina l,anesthesia. Spinal anesthesia reduces hemodynamic responses to intra venous epinephrine injection but is unlikely to reduce detection by po sitive SBP and HR criteria.