Prone versus knee-chest position for microdiscectomy: A prospective randomized study of intra-abdominal pressure and intraoperative bleeding

Study Design. Prospective randomized study. Objectives. To compare two support systems for positioning patients during microdiscectomy (i.e., prone on a modified Relton-Hall spine support vs. knee-chest position on an Andrews-type table) regarding their effects on intra-abdominal pressure and surgical bleeding. Summary of Background Data. Intra-abdominal pressure is an indicator of epidural venous pressure, which affects bleeding during microdiscectomy. The ideal patient's position during surgery reduces bleeding by minimizing abdominal compression and vertebral venous engorgement. The results of previous studies on the relationship between intra-abdominal pressure and blood loss during spinal surgery are not consistent, and hardly comparable because they used different measurement systems and support frames. Methods. A total of 30 patients with the American Society of Anesthesiologists physical status I or II undergoing elective, single-space lumbar microdiscectomy had their intra-abdominal pressure measured through a urinary bladder catheter, together with airway pressure: (1) supine after anesthesia induction; (2) in prone position (group P) or knee-chest position (group K), according to randomization; or (3) at the end of surgery before repositioning the patient supine. Results. Baseline intra-abdominal pressure did not differ between groups, and intra-abdominal pressure did not vary significantly from baseline in both groups throughout the study. Baseline airway pressure did not differ between groups. Airway pressure was significantly increased from baseline at the recording before incision in group K and at the end of surgery in both groups. Recordings before incision and at the end of surgery differed significantly from one another in both groups. Such airway pressure variations did not differ between groups. Bleeding was significantly more prominent in group K (P = 0.007). No correlation between bleeding and intra-abdominal pressure or airway pressure was found. Conclusions. Intra-abdominal pressure did not differ between prone position on a modified Relton-Hall frame and knee-chest position on an Andrew-type table. Both positions provide good conditions for lumbar microdiscectomy.