Use of a geographic information system to determine appropriate means of trauma patient transport

Objective: To determine whether a geographic information system (GIS) and h istorical transport data can be used to create a map that identifies locati ons (zones) from which either ambulance or helicopter transport will result in shorter out-of-hospital times. Methods: A retrospective, cross-sectiona l review:of a trauma registry was conducted in a two-county:region served b y a single trauma center. Data were gathered for all patients transported d irectly to the trauma center between 1993 and 1996. Incident locations and times from first 911 contact until arrival at the trauma center (out-of-hos pital time) were extracted. A GIS was used to create a reference map with a ll incident locations plotted and given z-coordinates corresponding to out- of-hospital time. Two contour surfaces were interpolated: one for all helic opter transports and one for all ground transports. Areas where the helicop ter surface was lower than the ambulance surface were designated air zones since helicopter transport resulted in shorter out-of-hospital times. The r emaining area was designated a ground zone since ambulance transport result ed in shorter out-of-hospital times. The mean out-of;hospital times were ca lculated for each mode of transport in both zones and were compared using a two-tailed t-test. Results: An air zone was identified beginning between 5 and 16 miles from the trauma center. Mean (+/-SD) out-of-hospital time fro m the air zone was 50 +/- 9 minutes for helicopter transport (n = 54) and 6 3 +/- 14 minutes for ambulance transport (n = 140). The difference between the means was 13 minutes (p < 0.000001; 95% CI = 8.95 to 17.05). Mean out-o f-hospital time from the ground zone was 68 +/- 16 minutes for helicopter t ransport (n = 122) and 32 +/- 14 minutes for ambulance transport (n = 2,047 ). The difference between-the means was 36 minutes (p < 0.000001; 95% CI = 33.59 to 38.41). Conclusions: A GIS and historical transport data can be us ed to create a map identifying locations from which either helicopter or am bulance transport will minimize out-of-hospital time. Inappropriate choice of transport models associated with increased out-of-hospital time.