Visual Versus Haematocrit Estimation of Intra-Operative Blood Loss in Open Posterior Spine Surgery: A Prospective Study.

Background: Bleeding during spine surgery can be significant enough to require intraoperative blood transfusion. Unnecessary blood transfusion is associated with significant risks. Therefore, the accurate determination of intraoperative blood loss is important. The visual estimation of blood loss is the commonly used method; however, its accuracy remains a subject of debate. Methodology: A total of 60 patients scheduled for posterior spine surgery were enrolled on the study. In the theatre, the patients' haematocrit level was determined before and after surgery using a hand-held hemoglobinometer, and a Bourke and Smith equation was used to calculate the blood loss. Blood loss was also visually estimated by the anaesthetist and documented. Statistical analysis was performed using SPSS 26 to compare both methods. Results: In all patients, the mean blood loss was 993.8ml by visual estimate and 754.6ml by haematocrit calculation (P = 0.006). When stratified, the mean blood loss for instrumented surgery was 1147.3ml for visual estimation, and 814.9ml for haematocrit calculation methods (P = 0.001). For lumbar spine surgeries, the mean blood loss was 1141ml for visual method and 773.9ml for the haematocrit method (P = 0.002). Conclusion: This study showed that the visual method of blood loss determination significantly overestimated the volume of intraoperative blood loss compared to the more objective haematocrit calculation method in patients undergoing posterior spine surgeries.