OBJECTIVE
To determine whether a geographic information system (GIS) and historical transport data can be used to create a map that identifies locations (zones) from which either ambulance or helicopter transport will result in shorter out-of-hospital times.
METHODS
A retrospective, cross-sectional review of a trauma registry was conducted in a two-county region served by a single trauma center. Data were gathered for all patients transported directly to the trauma center between 1993 and 1996. Incident locations and times from first 911 contact until arrival at the trauma center (out-of-hospital time) were extracted. A GIS was used to create a reference map with all incident locations plotted and given z-coordinates corresponding to out-of-hospital time. Two contour surfaces were interpolated: one for all helicopter transports and one for all ground transports. Areas where the helicopter surface was lower than the ambulance surface were designated air zones since helicopter transport resulted in shorter out-of-hospital times. The remaining area was designated a ground zone since ambulance transport resulted in shorter out-of-hospital times. The mean out-of-hospital times were calculated 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 from the air zone was 50 +/- 9 minutes for helicopter transport (n = 54) and 63 +/- 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-of-hospital time from the ground zone was 68 +/-16 minutes for helicopter transport (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 used to create a map identifying locations from which either helicopter or ambulance transport will minimize out-of-hospital time. Inappropriate choice of transport mode is associated with increased out-of-hospital time.
[1]
J S Smith,et al.
When is air medical service faster than ground transportation?
,
1993,
Air medical journal.
[2]
E. Lerner,et al.
Triage, Transportation, and Destination Decisions by Out-of-Hospital Emergency Care Providers
,
1998,
Prehospital and Disaster Medicine.
[3]
K. Koenig,et al.
Paramedic accuracy in estimated time of arrival: significance in the managed care environment.
,
1995,
Academic emergency medicine : official journal of the Society for Academic Emergency Medicine.
[4]
G. Jurkovich,et al.
Paramedic perception of elapsed field time.
,
1987,
The Journal of trauma.
[5]
C. A. Rosenberg,et al.
A comparison of prehospital estimated time of arrival and actual time of arrival to an emergency department.
,
1991,
The American journal of emergency medicine.
[6]
C. Branas,et al.
Urban trauma transport of assaulted patients using nonmedical personnel.
,
1995,
Academic emergency medicine : official journal of the Society for Academic Emergency Medicine.
[7]
R. Gordon,et al.
Taking to the skies.
,
1989,
Emergency.
[8]
H W Meislin,et al.
Prospective validation of a new model for evaluating emergency medical services systems by in-field observation of specific time intervals in prehospital care.
,
1993,
Annals of emergency medicine.
[9]
R E Burney,et al.
Ground versus air transport of trauma victims: medical and logistical considerations.
,
1986,
Annals of emergency medicine.