Abstract

Background Patient and surgical factors are known to influence operative blood loss in spinal fusion for Adolescent Idiopathic Scoliosis (AIS), but have only been loosely identified. To date, there are no established recommendations to guide decisions to pre-donate autologous blood, and the current practice is based primarily on surgeon preference. This study is designed to determine which patient and surgical factors are correlated with, and predictive of, blood loss during spinal fusion for AIS. Methods Retrospective analysis of 340 (83 M, 257 F, mean age 15.4) consecutive AIS patients treated by a single surgeon from 2000-08. Demographic (gender, age, height, weight, associated comorbidities), laboratory (hematocrit, platelet, PT/PTT/INR), standard radiographic, and perioperative data including complications were analyzed with a linear stepwise regression to develop a predictive model of blood loss. Results Estimated blood loss (EBL) was 911±775cc for posterior spinal fusion (PSF, n=183), 322±170cc for anterior spinal fusion (ASF, n=127), and 1277±821cc for combined procedures (n=30). For patients undergoing PSF, stepwise analysis identified gender, pre-op kyphosis and operative time to be the most important predictors of increased blood loss (p<0.05). For ASF, the mean arterial pressure (MAP) at incision and the operative time were predictive (p<0.05). The following formula was developed to estimate blood loss in PSF: Blood loss (ml) = C + Op-time (min) *(6.4) - Pre-op T2-T12 kyphosis (degrees) *(8.7) C= 233 if Male and -270 if Female. Conclusion We find gender, operative time, and preoperative kyphosis to be the most important predictors of increased blood loss in PSF for AIS. Mean arterial pressure and operative time were predictive of EBL in ASF. For posterior fusions, we also present a model that estimates blood loss preoperatively and can be used to guide decisions regarding pre-donation of blood and the use of antifibrinolytic agents.