Accuracy of visual estimation of external blood loss by trained first aiders

Abstract

Background: Uncontrolled external haemorrhage remains a leading cause of preventable death following trauma. Although bleeding-control initiatives, such as Stop the Bleed, have improved public awareness, the perceptual skill of accurately recognising and quantifying blood loss remains poorly understood and rarely taught. Visual estimation of external bleeding is widely used in prehospital care but is often unreliable, thus contributing to delayed intervention and inappropriate clinical responses. Aim and Objectives: This study aims to evaluate whether structured, feedback-driven training using the Merlin–Arbabi–Rhee (MAR) method could improve the accuracy of visual blood-loss estimation among trained first responders. The objectives are to measure baseline estimation accuracy, deliver a targeted educational intervention, and assess post-training improvement in both numerical estimation and haemorrhage classification. Design and Methods: A quantitative, quasi-experimental pre-/post-test design was adopted within a positivist paradigm. Thirty-one first responders from a non-governmental association participated. Sixteen calibrated photographic trauma scenarios depicting realistic blood pools were used. Participants estimated blood-loss volume and classified severity before and after a 90-minute MAR-based training session which incorporated structured feedback and debriefing. Data were analysed using descriptive statistics, paired nonparametric tests, and comparative visual analysis. Results: Post-training data demonstrated a 31% reduction in mean estimation error and a marked contraction in data variance. This indicated improved perceptual calibration. Three wound scenarios showed statistically significant gains (p < 0.05), with consistent directional improvement across all sixteen. Structured feedback proved particularly effective, and this accelerated the correction of perceptual errors and reinforced learning retention across scenarios. Participants also reported findings also indicate greater confidence and decisiveness in the recognition of catastrophic haemorrhage. Conclusion: The findings confirmed that visual estimation accuracy is a learnable cognitive skill that improves through structured exposure, feedback, and reflection. The MAR method provides a simple, scalable framework to develop perceptual precision in trauma education, thus enhancing early recognition and timely response to life-threatening bleeding.