Evaluation of the relationships between intravenous patient-controlled analgesia settings and morphine requirements among patients after lumbar spine surgery

To evaluate the association between daily morphine requirement and the intravenous patient-controlled analgesia (IVPCA) setting in patients undergoing spinal surgery. We conducted a retrospective analysis of 179 patients of American Society of Anesthesiologists physical status class I-III who underwent elective posterior lumbar spinal surgery and consented to IVPCA for postoperative pain control. The regi-mental solution contained morphine 1 mg/mL. The IVPCA program was set to deliver a priming dose of 1.5-4 mL, a basal infusion rate of 0-1.2 mL/hr, and a 0.5-1.5 mL bolus on demand with a 5-minute lockout interval. Demographic data, surgical procedures, analgesia program setting variables, 4-hour cumulative morphine dose and 11-point numeric rating scale for pain on postoperative days 1 and 2 were collected for comparison. The IVPCA requirement decreased gradually over time (p < 0.001). The number of vertebrae involved significantly influenced the daily morphine requirements (p = 0.01). None of the IVPCA settings, including continuous infusion, affected daily morphine requirements. On average, the analgesic requirement on postoperative day 2 was 18 less than that on postoperative day 1. The number of vertebrae involved was significantly associated with the daily IVPCA requirement. The IVPCA settings, including priming dose, basal infusion rate and bolus dose, did not affect the daily morphine requirements.