Hemodynamic responses to intravascular injection of epinephrine-containing epidural test doses in adults during general anesthesia

Background: Epidural anesthesia is sometimes initiated during general anesthesia, yet few data exist concerning efficacy of epinephrine-containing test doses. Methods: Thirty-six patients were randomized to receive either 0.5 MAC isoflurane, 1 MAC isoflurane, or 0.5 MAC each (1 MAC total) of isoflurane and nitrous oxide. Each subject received intravenous saline followed by three test doses containing 45 mg lidocaine with 7.5, 15, and 30 mu g epinephrine in a randomized, double-blind fashion. Heart rate and systolic, diastolic, and mean blood pressures were measured for 5 min after injection. Positive hemodynamic criteria identifying intravascular injection were determined from peak increases in hemodynamics during administration of saline. Dose-effect relationships between epinephrine and peak Increases in hemodynamics were assessed with linear regression. Minimum required doses of epinephrine to produce peak positive hemodynamic increases on average were determined from linear regression. Results: Positive hemodynamic criteria were identified as increases in heart rate greater than or equal to 8 beats/min, systolic blood pressure greater than or equal to 13 mmHg, diastolic blood pressure greater than or equal to 7 mmHg, and mean blood pressure greater than or equal to 9 mmHg, Significant dose-effect relationships were observed for epinephrine and peak increases in hemodynamics (correlation coefficients ranged from 0.61-0.91). Minimum required doses of epinephrine ranged from 6 to 19 mu g depending on hemodynamic measurement and anesthetic group. Conclusions: Hemodynamic responses to intravascular injection of test doses vary with dose of epinephrine and depth and type of general anesthetic used. Thus, the 15 mu g epinephrine contained in the standard test dose may not be sufficient during all anesthetic conditions.