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

Background and Objectives: Epinephrine modifies the hemodynamic response to epidural local anesthetic; effects on respiratory gas exchange are not kno wn. We hypothesized that epidural epinephrine would increase oxygen consump tion and carbon dioxide production. Methods: Twelve healthy patients (age, 22 to 46 years) undergoing surgery o n the knee were randomly assigned to receive either 2% lidocaine (group L) or 2% lidocaine with epinephrine 5 mu g . mL(-1) (group E), approximately 2 0 mt, over 10 minutes via lumbar epidural catheter. Total-body oxygen consu mption (VO2) and carbon dioxide production (VCO2) were determined by indire ct calorimetry; hemodynamic measurements were obtained by noninvasive thora cic electrical bioimpedance. Values of VO2, VCO2, heart rate (HR), cardiac index (CI), and mean arterial blood pressure (MAP) were determined every mi nute and averaged every 5 minutes for 30 minutes. Comparisons were made wit h analysis of variance (ANOVA) (within groups) and t-tests (between groups) . Differences were considered statistically significant if P <.05. Results: VO2 did not change in either group, while VCO2 increased significa ntly 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%; gro up 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. Conclusions: The addition of epinephrine, 5 mu g . mL(-1), to the epidural injection of 2% lidocaine is associated with changes not only in hemodynami cs, but also in respiratory gas exchange.