Background and Objectives To quantitate the possible nitrogen-sparing effect induced by continuous epidural block during the flow phase of surgical trauma, protein kinetics were measured in patients undergoing colorectal surgery and receiving a constant protein intake.

Methods Epidural block was established in two groups of eight patients each before surgery with 0.75% bupivacaine, and after surgery sensory analgesia (T4 to S5) was maintained with 0.25% bupivacaine. In the first group, the neural block was maintained for 24 hours, while in the second group, it was maintained for 48 hours. Protein synthesis and breakdown and amino acid oxidation were measured by a stable isotope dilution technique using a primed constant infusion of labeled leucine. Changes in oxygen consumption (O₂) and carbon dioxide production (CO₂) were estimated by indirect calorimetry.

Results All measurement were made before and 2 and 4 days after surgery. Whole body protein synthesis and breakdown and O₂ and CO₂ increased significantly (P < .05) in the 24-hour group after surgery compared with presurgical levels during the second postoperative day. In contrast, no significant increase was found in the 48-hour group, which had an effective neural block during the isotope infusion. On the fourth postoperative day, whole body protein metabolism was similar in both groups.

Conclusions Direct application of isotope tracer methodology to acute studies confirms the beneficial effects of epidural block with local anesthetics in modulating body nitrogen losses.