External blood loss estimation using the MAR Method

BackgroundAn element lacking in medical education is training to estimate blood volumes. Therefore, health care workers currently use visual estimation as their only means of determining blood volumes, which has shown to be highly inaccurate. This study proposes and tests a new method using one's fist to determine external blood loss.MethodsIncrements of human whole blood were measured and used to compare fist size to surface area of blood present. A formula was created averaging blood per fist, hereafter known as the MAR Method. Two scenarios were staged using set quantities of blood (75 and 750 mL). Participants estimated blood volumes before and after being taught the MAR Method in a 1-minute session. Errors in estimation before and after using the MAR Method were compared.ResultsThe MAR Method was created using a fist to cover a surface area of blood that equals 20 mL. A total of 74 participants had errors of 120% and 73% for visualization of the small and large pools, respectively. For the smaller volume, the average error from the mean decreased by 76% (P < .0001), and the interquartile range of errors decreased by 60%. For the larger volume, the average error from the mean reduced by 40% (P < .0001), and the interquartile range of errors reduced by 45%.ConclusionUse of the MAR Method improves blood volume estimations. After less than 1 minute of instruction, participants were able to determine blood volumes with improved accuracy and precision.