Factors influencing intraoperative blood loss in orthognathic surgery.

This retrospective study aimed to identify factors of importance for intraoperative blood loss relative to total blood volume in patients undergoing orthognathic surgery. The study included 356 patients treated consecutively at a Danish university hospital between 1 January 2010 and 31 December 2012. Inclusion criteria were (1) patient age >/=18 years and (2) patient undergoing a three-piece Le Fort I osteotomy, a bilateral sagittal split osteotomy, or a combination of the two. The patient-specific relative blood loss was calculated as a percentage by dividing the intraoperative blood loss by the estimated preoperative total blood volume, and then correlated with body mass index (BMI), age, sex, operating time, and treatment modality in a multivariate stepwise regression analysis. Operating time (P<0.001), BMI (P<0.001), and treatment modality (P<0.001) had a significant impact on relative blood loss; no significant effect of age or sex was observed. The coefficient of determination of relative blood loss was R(2)=0.34. In conclusion, this study introduces relative blood loss as a patient-specific measure of intraoperative blood loss. Average relative blood loss in this patient sample was 6.5%. Extensive surgery, a prolonged operating time, and reduced BMI significantly increase the intraoperative relative blood loss in patients undergoing orthognathic surgery.