Respiratory gas exchange and hemodynamics during lumbar epidural anesthesia: effects of lidocaine with and without epinephrine.

Abstract

Epinephrine modifies the hemodynamic response to epidural local anesthetic; effects on respiratory gas exchange are not known. We hypothesized that epidural epinephrine would increase oxygen consumption and carbon dioxide production. Twelve healthy patients (age, 22 to 46 years) undergoing surgery on the knee were randomly assigned to receive either 2% lidocaine (group L) or 2% lidocaine with epinephrine 5 microg x mL(-1) (group E), approximately 20 mL, over 10 minutes via lumbar epidural catheter. Total-body oxygen consumption (VO2) and carbon dioxide production (VCO2) were determined by indirect calorimetry; hemodynamic measurements were obtained by noninvasive thoracic electrical bioimpedance. Values of VO2, VCO2, heart rate (HR), cardiac index (CI), and mean arterial blood pressure (MAP) were determined every minute and averaged every 5 minutes for 30 minutes. Comparisons were made with analysis of variance (ANOVA) (within groups) and t-tests (between groups). Differences were considered statistically significant if P < .05. VO2 did not change in either group, while VCO2 increased significantly by 22% at 20 minutes in group E. Increases in HR were apparent in both groups, with significantly greater increases in group E (group L, 13%; group E, 21%). CI did not change in group L, but increased by 41% in group E. MAP decreased significantly by 11% in group E, but did not change in group L. The addition of epinephrine, 5 microg x mL(-1), to the epidural injection of 2% lidocaine is associated with changes not only in hemodynamics, but also in respiratory gas exchange.