How well do emergency medical dispatch priority decisions match actual patient need?

Study objective: To quantify the extent of over-dispatching of advanced life support (ALS) personnel to situations where their skills are not utilized, in order to determine how efficiently the priority dispatch protocol under study allocates ALS resources.
Design: Retrospective review of all rescue squad patient records for incidents of unconsciousness/fainting from September 1999 - April 2000.
Setting: Albemarle County, Virginia, including the City of Charlottesville.
Participants: Individuals for whom an emergency call was initiated for an episode of unconsciousness/fainting.
Results: The priority dispatch protocol resulted in a 2.5% under-dispatch rate for basic life support (BLS) units and a 43.7% over-dispatch rate for ALS units. ALS treatment was only needed 31.9% of the time when ALS units were dispatched. Many cases requiring ALS treatment involved only IV initiation or EKG interpretation. The underdispatch rate was 0.7% and the over-dispatch rate 12.5% for ALS treatments more aggressive than IVs or EKG readings. The sensitivity of the protocol to need for ALS treatment was 92.7%, and the specificity was 33.3%. The positive and negative predictive values were 42.2% and 89.7%, respectively. The protocol was more accurate in predicting when ALS treatment would not be utilized than when it would be utilized.
Conclusion: Priority-based dispatch protocols must accurately predict need for ALS treatment to be effective. This study found little evidence of under-dispatching but considerable over-dispatching of ALS units. A more detailed protocol might reduce over-dispatching without increasing under-dispatching or jeopardizing patient safety.