Identification of patients to include in trauma audit: a modification of the pre-chart

Trauma audit is commonly focused using a Pre-Chart to illustrate calculations made using the TRISS model. A line is drawn at Ps = 0.5 to divide expected survivors and nonsurvivors. The use of this cut-off in a severely injured population was examined. The 'M statistic' for a group of injured patients selectively triaged to a Trauma Centre was calculated. The ideal cut-off point between predicted outcomes when using the TRISS model to focus trauma audit in this population was determined using a Receiver Operating Characteristic (ROC) curve. For this population the TRISS 'M statistic' was 0.71 (indicating a significantly different case mix from the reference database) and the best cut-off point was at Ps = 0.76. Trauma audit in populations with a case mix of injury severity different from the reference database should use a different Ps line to define unexpected outcomes.