OBJECTIVE--To assess the effect of the London helicopter emergency medical service on survival after trauma. DESIGN--Prospective comparison of outcomes in cohorts of seriously injured patients attended by the helicopter and attended by London ambulance service land ambulances crewed by paramedics. SETTING--Greater London. SUBJECTS--337 patients attended by helicopter and 466 patients attended by ambulance who sustained traumatic injuries and died, stayed in hospital three or more nights, or had other evidence of severe injury and who were taken to any one of 20 primary receiving hospitals. MAIN OUTCOME MEASURE--Survival at six months after the incident. RESULTS--After differences in the nature and severity of the injuries in the two cohorts were accounted for the estimated survival rates were the same (relative risk of death with helicopter = 1.0; 95% confidence interval 0.7 to 1.4). An analysis with trauma and injury severity scores (TRISS) found 16% more deaths than predicted in the helicopter cohort but only 2% more in the ambulance cohort. There was no evidence of a difference in survival for patients with head injury but a little evidence that patients with major trauma (injury severity score > or = 16) were more likely to survive if attended by the helicopter. An estimated 13 (-5 to 39) extra patients with major trauma could survive each year if attended by the helicopter. CONCLUSION--Any benefit in survival is restricted to patients with very severe injuries and amounts to an estimated one additional survivor of major trauma each month. Over all the helicopter caseload, however, there is no evidence that it improves the chance of survival in trauma.
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