When birds can't fly: an analysis of interfacility ground transport using advanced life support when helicopter emergency medical service is unavailable.

Background: Helicopter emergency medical service (HEMS) transport of trauma patients is costly and of unproven benefit. Recent retrospective studies fail to control for crew expertise and therefore compare highly trained advance life support with less-trained basic life support crews. The purpose of our study was to compare HEMS with ground, interfacility transport while controlling for crew training.