Introduction: Air ambulances are scarce and expensive assets. To be used efficiently they need to be dispatched to patients who will gain the most benefit.
Objective: To identify factors associated with low standdown rates and high conveyance rates, suggesting efficient use of air ambulance resources.
Method: Eight months' call history for a single United Kingdom air ambulance (National Health Service (NHS) paramedic/doctor crew, charity-funded aircraft) covering two English counties was retrospectively analyzed. Standdown and conveyance rates were calculated for (medical, trauma, road traffic collision (RTC)) types of call from the three control rooms involved in dispatching the helicopter, each of which used a different dispatch model: Regional air desk, local area dispatcher, and combined regional first response/air ambulance desk.
Results: The air ambulance was dispatched 878 times during the study period. The overall stand-down rate was 34.7% and conveyance rate 29.4%. Factors associated with higher conveyance and lower stand-down rates included non-RTC traumatic incidents, RTCs involving bicycles and motorcycles, and dispatch by a regional air desk or local area dispatcher. Factors associated with lower conveyance and higher stand down-rates included high crew request rates, medical calls, RTCs (particularly those involving cars and lorries/ trucks), and dispatch by a combined regional responder/air ambulance desk.
Conclusion: These results suggest that a dispatcher's intuition based on routinely-gathered emergency call information is not always sufficient to predict benefit of a helicopter. Some high-risk mechanism injuries are more likely to require helicopter conveyance, but further caller interrogation or secondary dispatch may provide more sensitive prediction. A balance needs to be achieved between unnecessary mobilization and delays caused by waiting for a crew update. Further analysis of AMPDS codes could inform design of HEMS dispatch protocols. Reducing unnecessary mobilization could save charitable funds and target resources to patients most in need.