Controlling for the severity of injuries in emergency medicine research.

The injury severity score (ISS) and age have been used retrospectively to control for trauma severity. Other control variables such as the revised trauma score (RTS) and the TRISS method (which estimates the probability of survival for each patient) additionally require that values of blood pressure, Glasgow coma scale, and respiratory rate, be recorded in the emergency department. The authors question when the RTS, ISS, the ISS and age, or the probability of survival calculated using the TRISS method should be used to control for severity of injuries in trauma research. Relations between predictor variables and (1) survival to hospital discharge, (2) hospital length of stay for survivors, and (3) length of ICU stay were compared by cause of injury: penetrating, motor vehicle accident, low fall, or other blunt. Data were collected over 12 months for 2,914 consecutive adult patients who died or stayed in five nontrauma and three trauma centers for 48 hours or more. For survival, the false-negative rates of probability of survival calculated using the TRISS method were approximately half that of the ISS and age; no variable adequately explained survival among those with low falls. Combinations of ISS, RTS, and age explained the most variation in lengths of hospital stay among survivors, while ISS explained the most variation in lengths of intensive care unit (ICU) stay. Researchers should consider the ISS with RTS and age to control for severity when lengths of hospital or ICU stay are studied. The TRISS method should be used in studies of survival. In both cases, the RTS which requires data collection in the emergency department must be calculated.