Differences in mortality rates among trauma patients transported by helicopter and ambulance in Maryland.

INTRODUCTION: A comprehensive state-wide emergency medical services and helicopter transport system has been developed in the State of Maryland on the principle that early definitive care improves patient outcomes. The purpose of this study was to determine if empirical data exist to support the theory that air medical transportation services provided by the Maryland State Police (MSP) Aviation Division contribute to an improved trauma patient survival rate in Maryland.
METHODS: A retrospective study was conducted on the records of all patients transported by helicopter or ground ambulance and admitted to the R Adams Cowley Shock Trauma Center (STC) of the University of Maryland Medical System. Data were obtained from the Maryland Institute of Emergency Medical Services Systems (MIEMSS) Shock Trauma Clinical Registry for the period January 1988 through July 1995, covering 23,002 patients. Patients included those transported directly from the scene of injury to the STC as well as those from interfacility transfers. All patients were stratified by injury severity and compared by outcome (mortality) using Mantel-Haenszel statistics.
RESULTS: During the study period, 11,379 patients were transported by ground and 11,623 were transported by MSP helicopter. The mean Injury Severity Score (ISS) for patients transported by ground was 12.7 (SD = 12.52) and the mean ISS for patients transported by air was 14.6 (SD = 13.42), p < 0.001. Among patients classified as having a high index of injury severity, the mortality rate was lower among those transported by MSP helicopter than among those transported by ambulance. The mortality rate was significantly lower for air transported patient with an ISS higher than 31.
CONCLUSION: The State of Maryland has demonstrated a commitment to its citizenry and invested heavily in its public safety air medical service. This study suggests the rapid air transport of victims of traumatic events by specialized personnel in Maryland has a positive effect on the outcome of severely injured patients. Further research is necessary to clarify the causal relationships in order to more fully elucidate the value of this resource.