Effect of a Continuous Peripheral Nerve Block on the Inflammatory Response in Knee Arthroplasty

Experimental nerve block in animals inhibits the inflammatory response. The purpose of this study was to determine to what extent a 48-hour local anesthetic block of all afferent and efferent nerve fibers of the knee area has an impact on postoperative inflammatory response. Twelve patients scheduled for primary total knee arthroplasty received spinal anesthesia, and then were randomly allocated to either patient-controlled analgesia with morphine (n = 6) or a combination of continuous lumbar plexus and sciatic nerve blocks (continuous peripheral nerve block; CPNB) with ropivacaine 0.2% for 48 hours. Blood samples were collected before surgery and at 3, 8, 24, and 48 hours after surgical incision to measure plasma glucose, serum insulin and cortisol, C-reactive protein, interleukin-6, and leukocyte count. Pain visual analog scale at rest and on knee flexion were recorded and complications classified. Visual analog scale was lower in the CPNB group at rest and on knee flexion on postoperative days 1 and 2 ( P < .05). There were no differences in circulating levels of glucose, insulin, and cortisol. C-reactive protein and leukocyte count were lower in the CPNB group ( P < .05). There was a positive correlation between the peak leukocyte count and the inflammatory markers ( P < .03). Three patients in the patient-controlled analgesia group and one in the CPNB group had complications requiring conservative management. Continuous lumbar plexus and sciatic nerve blocks with ropivacaine contribute to the attenuation of the postoperative inflammatory response.