Primary Triage in a Mass-casualty Event Possesses a Risk of Increasing Informational Confusion: A Simulation Study Using Shannon’s Entropy

Introduction Primary triage in a mass-casualty event setting using low-visibility tags may lead to informational confusion and difficulty in judging triage attribution of patients. In this simulation study, informational confusion during primary triage was investigated using a method described in a prior study that applied Shannon's Information Theory to triage. Hypothesis Primary triage using a low-visibility tag leads to a risk of informational confusion in prioritizing care, owing to the intermingling of pre- and post-triage patients. It is possible that Shannon's entropy evaluates the degree of informational confusion quantitatively and improves primary triage. The Simple Triage and Rapid Treatment (START) triage method was employed. In Setting 1, entropy of a triage area with 32 patients was calculated for the following situations: Case 1 - all 32 patients in the triage area at commencement of triage; Case 2 - 16 randomly imported patients to join 16 post-triage patients; Case 3 - eight patients imported randomly and another eight grouped separately; Case 4 - 16 patients grouped separately; Case 5 - random placement of all 32 post-triage patients; Case 6 - isolation of eight patients of minor priority level; Case 7 - division of all patients into two groups of 16; and Case 8 - separation of all patients into four categories of eight each. In Setting 2, entropies in the triage area with 32 patients were calculated continuously with each increase of four post-triage patients in Systems A and B (System A - triage conducted in random manner; and System B - triage arranged into four categories). In Setting 1, entropies in Cases 1-8 were 2.00, 3.00, 2.69, 2.00, 2.00, 1.19, 1.00, and 0.00 bits/symbol, respectively. Entropy increased with random triage. In Setting 2, entropies of System A maintained values the same as, or higher than, those before initiation of triage: 2.00 bits/symbol throughout the triage. The graphic waveform showed a concave shape and took 3.00 bits/symbol as maximal value when the probability of each category was 1/8, whereas the values in System B showed a linear decrease from 2.00 to 0.00 bits/symbol. Informational confusion in a primary triage area measured using Shannon's entropy revealed that random triage using a low-visibility tag might increase the degree of confusion. Methods for reducing entropy, such as enhancement of triage colors, may contribute to minimizing informational confusion. Ajimi Y , Sasaki M , Uchida Y , Kaneko I