Estimating intraoperative blood loss is one of the daily challenges for clinicians. Despite the knowledge of the inaccuracy of visual estimation by anaesthetists and surgeons, this is still the mainstay to estimate surgical blood loss. This review aims at highlighting the strengths and weaknesses of currently used measurement methods. A systematic review of studies on estimation of blood loss was carried out. Studies were included investigating the accuracy of techniques for quantifying blood loss in vivo and in vitro. We excluded nonhuman trials and studies using only monitoring parameters to estimate blood loss. A meta-analysis was performed to evaluate systematic measurement errors of the different methods. Only studies that were compared with a validated reference e.g. Haemoglobin extraction assay were included. 90 studies met the inclusion criteria for systematic review and were analyzed. Six studies were included in the meta-analysis, as only these were conducted with a validated reference. The mixed effect meta-analysis showed the highest correlation to the reference for colorimetric methods (0.93 95% CI 0.91–0.96), followed by gravimetric (0.77 95% CI 0.61–0.93) and finally visual methods (0.61 95% CI 0.40–0.82). The bias for estimated blood loss (ml) was lowest for colorimetric methods (57.59 95% CI 23.88–91.3) compared to the reference, followed by gravimetric (326.36 95% CI 201.65–450.86) and visual methods (456.51 95% CI 395.19–517.83). Of the many studies included, only a few were compared with a validated reference. The majority of the studies chose known imprecise procedures as the method of comparison. Colorimetric methods offer the highest degree of accuracy in blood loss estimation. Systems that use colorimetric techniques have a significant advantage in the real-time assessment of blood loss.

Background: Particularly for protracted bleeding situations, the realization of a relevant blood loss is necessary for early initiation of therapy to avoid hemodynamic instability and shock. The frequently used visual assessment of blood loss is known to be incorrect. An innovative option to address this problem is a mobile application using colorimetric image correction and analysis. Methods: The objective of this study was to evaluate the clinical applicability and accuracy of a novel mobile device application using colorimetric image correction and analysis for blood loss estimation. Scenarios of blood-filled surgical sponges were created to evaluate the accuracy of colorimetric-based blood loss estimation and visual and gravimetric blood loss estimation. Results: Fifty-three anesthesiologists ran through the scenarios. The estimated blood loss correlated the least with the reference blood loss in the visual technique (Rho: 0.52; P < 3.7Â10 À16 ), followed by the gravimetric technique (Rho: 0.73; P ¼ 2.8Â10 À05 ). The best correlation was found in the colorimetric blood loss measurement (Rho: 0.77; P ¼ 3.53Â10 À06 ). A median overestimation per scenario of 133.0 mL (interquartile range [IQR] 33.0 mL-283.0 mL) was observed when using the visual method, whereas 32.5 mL (IQR 10.8 mL-44.0 mL) was overestimated with the gravimetric method and 31 mL (IQR 17.0 mL-42.8 mL) with the colorimetric method. Especially in the case of blood loss underestimation, the application has the least deviation from the reference. Conclusion: The blood loss measured in the sponges correlated strong with the reference blood loss, showing the smallest median overestimation and the smallest deviation in underestimation. The visual estimation shows serious errors, where the gravimetric method is prone to errors, especially in dilution. The colorimetric method offers an easily implementable possibility to monitor blood loss in real time and to initiate early diagnostic and therapeutic measures in case of persistent blood loss. The influence of real-time estimation of colorimetric blood loss on transfusion decisions should be the subject of future studies.

Background The intraoperative blood loss is estimated daily in the operating room and is mainly done by visual techniques. Due to local standards, the surgical sponge colours can vary (e.g. white in US, green in Germany). The influence of sponge colour on accuracy of estimation has not been in the focus of research yet. Material and methods A blood loss simulation study containing four “bleeding” scenarios each per sponge colour were created by using expired whole blood donation samples. The blood donations were applied to white and green surgical sponges after dilution with full electrolyte solution. Study participants had to estimate the absorbed blood loss in sponges in all scenarios. The difference to the reference blood loss was analysed. Multivariate linear regression analysis was performed to investigate other influence factors such as staff experience and sponge colour. Results A total of 53 anaesthesists participated in the study. Visual estimation correlated moderately with reference blood loss in white (Spearman's rho: 0.521; p = 3.748*10 −16 ) and green sponges (Spearman's rho: 0.452; p = 4.683*10 −12 ). The median visually estimated blood loss was higher in white sponges (250ml IRQ 150–412.5ml) than in green sponges (150ml IQR 100-300ml), compared to reference blood loss (103ml IQR 86–162.8). For both colour types of sponges, major under- and overestimation was observed. The multivariate statistics demonstrates that fabric colours have a significant influence on estimation (p = 3.04*10 −10 ), as well as clinician’s qualification level (p = 2.20*10 −10 , p = 1.54*10 −08 ) and amount of RBL to be estimated (p < 2*10 −16 ). Conclusion The deviation of correct blood loss estimation was smaller with white surgical sponges compared to green sponges. In general, deviations were so severe for both types of sponges, that it appears to be advisable to refrain from visually estimating blood loss whenever possible and instead to use other techniques such as e.g. colorimetric estimation.