Reduction of Mean Arterial Pressure at Incision Reduces Operative Blood Loss in Adolescent Idiopathic Scoliosis.

Background: Spinal fusion surgery for adolescent idiopathic scoliosis (AIS) has been associated with significant blood loss and transfusion requirements. Reduction of mean arterial pressure (MAP) has benefits, but has been debated. This study aimed to analyze hypotensive anesthesia (MAP less than 65 mm Hg) at incision for its effect on blood loss.

Methods: Retrospective analysis of 327 AIS patients treated by a single surgeon from 2000 to 2008. We recorded demographic, laboratory, and radiographic measurements and perioperative data, including complications. We estimated MAP from the anesthesia flow sheet at incision (I-MAP) and during the entire surgery (Avg MAP). Patients were stratified into 3 groups: low (MAP less than 65), medium (MAP 65-75), or high (MAP greater than 75). We also evaluated the effect of elevated blood pressure at incision. The groups were as follows: reduced (I-MAP less than Avg MAP), stable (I-MAP = Avg MAP), or elevated (I-MAP greater than Avg MAP). We performed comparisons using analysis of variance with Tukey's Multiple Comparison Test. Blood loss was recorded as absolute volume and percent total blood volume (%EBV).

Results: Of the 327 patients (mean age, 15 years; range, 10-21 years; 248 females), 129 received blood transfusions (29% allogenic). There was a reduction in blood loss comparing low (584 mL; 14% EBV) versus high I-MAP (871 mL; 20.3% EBV) (p = .03). Likewise, an elevated blood pressure at incision led to increased blood loss: reduced, 510 mL, 11.5% EBV; stable, 735 mL, 17.6% EBV; and elevated, 1,033 mL, 24.9% EBV (p = .000-.02). Operative time was decreased in the low group by up to 48 minutes (p = .002), as was blood loss per minute (2.6 mL/min vs. 3.8 mL/min). There were no complications related to the use of hypotension.

Conclusions: Induction of hypotensive anesthesia (MAP less than 65 mm Hg) at incision reduces operative blood loss by 33%. In addition, elevations in blood pressure at incision increase blood loss by 29%, and operative time by 29 minutes.