Surrogate markers of transport distance for out-of-hospital cardiac arrest patients

Background. Transport of out-of-hospital cardiac arrest (OHCA) patients expeditiously to appropriately equipped hospitals is of paramount importance. Objective. We sought to test the correlation of the centroids of geographic units with the actual transport distance for OHCA patients in order to determine the most appropriate surrogate marker of location for future planning, protocol development, and research projects. Methods. This was a prospective, observational analysis of OHCA events in Portland, Oregon. Using geographic information systems (GISs), the locations of OHCA events and receiving hospitals were identified and geocoded for visual inspection and analysis. Transport distance was calculated via network transport distance and Euclidean distance from multiple surrogate markers of location (centroids of ZIP code, census tract, census block group, and census block). Actual distance from the location of the event was then compared with these surrogate markers to determine the accuracy of alternative markers of OHCA location. Results. Two hundred seventy patients had location data recorded, 163 of whom were transported to a hospital for further care. The median transport distance was 5.17 miles. The transport distance of OHCA patients from the centroid of the census block had the best correlation (R ² = 0.99) with actual transport distance, whereas the use of the centroid of ZIP codes as a surrogate location had the lowest correlation (R ² = 0.21). Conclusions. The use of centroids of census blocks via network distance is a valid surrogate for actual location of an OHCA event when calculating transport distance.