The MAR method versus the visual estimation method in predicting external blood loss: a randomized controlled study

Abstract Accurately estimating blood loss is critical for managing hemorrhagic shock in prehospital and hospital settings. The Visual Estimation (VE) method is widely used, while the MAR method proposes using a fist measurement to estimate external blood on flat surfaces. A randomized, double-blind, parallel-group, controlled, and educational study was conducted involving 140 medical and paramedic students. The study compared the accuracy and duration of blood loss estimates made with the MAR and VE methods. The secondary objective was to assess whether MAR estimates varied by participants’ height, weight, or gender. Three simulated stations featured three different, non-absorbent, flat surfaces containing 75 mL, 150 mL, or 750 mL of blood. Participants were divided into two groups (Group 1: VE method, n1 = 70; Group 2: MAR method, n2 = 70) and asked to estimate blood loss using the assigned method at each of the three stations (Station 1 to Station 3). Analytical tests evaluated absolute differences and percentage errors in both intergroup and intragroup comparisons. In the intergroup analysis, comparisons were made between Group 1 using the VE method and Group 2 using the MAR method. In the intragroup analysis, Group 1 was compared using the VE method versus the MAR method. Given the non-normality, repeated measures were analyzed using F1 LD F1 and F2 LD F1 models via nparLD in R. Improvement in estimations after the MAR method was evidenced by a reduction in errors relative to the actual blood volumes, and this was statistically significant. It also reduced outlier estimates and took longer. The MAR volume estimates were not affected by participants’ phenotypic characteristics. In conclusion, incorporating the MAR method into structured clinical skills training for external bleeding management could be beneficial. Trial registration: ClinicalTrials.gov Identifier NCT06855472 (18/02/2025).