Continuous Opioid Infusion for Scoliosis Fusion Surgery

Abstract

Paraplegia is the major risk involved in reconstructive surgery for scoliosis with fusion. To detect spinal cord dysfunction intraoperatively, somatosensory cortical-evoked potential (SCEP) monitoring and a wake-up test or a combination of the two is generally used. Our pilot studies indicated that a balanced anesthesia technique consisting of nitrous oxide, narcotics, and a muscle relaxant is well-suited both for SCEP monitoring as well as for wake-up tests. However, at times the intermittent administration of narcotics adversely affected SCEP interpretation and wake-up tests. To facilitate both SCEP interpretation and wake-up tests, we employed N2O/O2 with continuous infusion of narcotics and compared it with intermittent bolus administration of narcotics in 35 patients. For our purposes fentanyl (FE) was assumed to be 100 times more potent than morphine (MS). Our first 13 patients were studied using bolus increments of either MS (5-10 mg) every 30-40 minutes or FE (50-100 micrograms) every 20-30 minutes. The remaining 22 patients were studied during continuous infusions of either MS at a rate ranging from 150-250 micrograms X kg-1 X hr-1 or FE at a rate ranging from 1.5 to 2.5 micrograms X kg-1 X hr-1. Continuous infusions reduced total narcotic requirements (P less than 0.005). In addition, the technique produced stable suppression of SCEPs and made it easier to interpret surgically induced SCEP changes. Wake-up tests were smooth and repeatable. Patients who received fentanyl infusions fared better than those receiving MS in that they did not require postoperative respiratory support. Continuous infusions of fentanyl are useful in reconstructive spinal surgery for scoliosis with monitoring.