Hemodynamic responses to an epinephrine test dose in adults during epidural or combined epidural-general anesthesia

The efficacy of an epinephrine test dose during epidural and combined epidural-general anesthesia is unknown. Thirty-two patients were randomized to receive 2% lidocaine at either a high (25 mL) or low (12 mL) thoracic level of epidural anesthesia followed by general anesthesia with 1 minimum alveolar anesthetic concentration nitrous oxide and isoflurane. A 15-micrograms epinephrine test dose was intravenously administered prior to placement of the lumbar epidural catheter, 20 min after initiation of epidural anesthesia, and after 10 min of stable end-tidal concentrations of general anesthesia. Only high thoracic levels (T-5) of epidural anesthesia reduced the peak systolic blood pressure response to epinephrine (34 +/- 17 vs 18 +/- 11 mm Hg, control versus epidural stage; P < 0.05) and reduced the peak heart rate response when combined with general anesthesia (31 +/- 11 vs 15 +/- 8 bpm; P < 0.05). Incidences of identification of intravascular injection from hemodynamic responses were similarly reduced for systolic blood pressure (100% vs 44%) and heart rate (100% vs 38%). The standard 15-micrograms epinephrine test dose is unaffected by low thoracic levels of epidural anesthesia, but may have decreased sensitivity for detection of intravascular injection during high thoracic levels of epidural anesthesia, especially during general anesthesia.