Purpose: Pre-hospital triage of mass casualty event victims is a critical resource allocation process that has not been extensively studied. We created a theoretical model of triage as a diagnostic test to quantify the relationship between triage, casualty load, hospital capacity, and mortality.
Methods: We developed a discrete event simulation of mass casualty triage by first creating a population of critically and non-critically injured patients, applying a triage test designed to distinguish between critical and non-critical casualties, and then evaluating the consequences of the triage decision. Hypothetical ROC curves were generated from available data. We found conflicting reports of time-dependent mortality for critical casualties, and chose three representative curves: late (post-6 hours), linear (steady decline of ~12% per hour), and exponential (rapid decline after "golden hour"). We examined casualty loads ranging from 100 to 500 patients, percentage of critical patients ranging from 20-33%, and available emergency department/operating room tandems (EDORs – a measure of available treatment capacity) ranging from 1-9.
Results: We present results for the 7-EDOR, 100-patient, 25% critical patient scenario with linear time-dependent mortality across a range of sensitivities for the triage algorithm. Worst case critical mortality ratio is 55% (critical patients are treated last), best case is 34% (critical patients are triaged perfectly), and with no triage is 48%. High sensitivity for identifying critical casualties (and correspondingly lower specificity) leads to a critical mortality ratio (CM) of 41%, low sensitivity leads to CM of 42%, and standard triage (favoring neither high nor low sensitivity) leads to CM of 39%. This relationship can be developed across a range of numbers of assumptions including: EDOR number, patient load, time dependent mortality rate, and triage accuracy.
Conclusion: The number of total casualties and ratio of casualties to treatment resources determines whether a higher or lower sensitivity triage process yields lower mortality. However, for a wide range of mass casualty scenarios, it appears that implementing triage at typical sensitivity levels (ie, 80% to 90%) minimizes critical patient mortality. Implementing a triage strategy will reduce critical patient mortality, regardless of whether a high or low sensitivity test is used.