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Prehosp Disaster Med. 1997 Oct-Dec;12(4):274-7.

The wake-effect--emergency vehicle-related collisions.

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Gold Cross Ambulance and Medical Priority Consultants, Salt Lake City, UT 84111, USA.



Emergency medical vehicle collisions (EMVCs) occurring during initial response and with patient transport have been a long-standing problem for emergency medical services (EMS) systems. Experience suggests "wake-effect" collisions occur as a result of an EMS vehicle's transit, but do not involve the emergency medical vehicle (EMV). Substantiating the existence and magnitude of wake-effect collisions may have major implications regarding the manner of EMV response.


Paramedics will report that wake-effect collisions do occur and that they occur more frequently than do EMVCs.



Survey analysis.


Thirty paramedics employed by the Salt Lake City (Utah) Fire Department and 45 paramedics employed by Salt Lake County Fire Department. Geographic Area: Service area has population of 650,000 and is urban, suburban, and rural.


The survey consisted of three open-ended questions concerning years on the job, EMVCs, and wake-effect collisions.


The mean value for the number of EMVCs and wake-effect EMVCs, along with the 0.95 confidence intervals (0.95 CI) were determined.


Seventy-three surveys were analyzed. Sixty EMVCs and 255 wake-effect collisions were reported. Overall, the mean value for the number EMVCs per respondent was 0.82 (0.60-1.05) and for wake-effect collisions 3.49 (2.42-4.55). The mean values for EMVC's for each service were 0.86 (0.50-1.38); 0.80 (0.50-11.0). For wake-effect collisions the mean values were 4.59 (2.83-6.35); and 2.76 (1.46-4.06) respectively.


This study suggests that the wake-effect collision is real and may occur with greater frequency than do EMVCs. Significant limitations of this study are recall bias and misclassification bias. Future studies are needed to define more precisely wake-effect collision prevalence and the resulting "cost" in regards to injury and vehicle/property damage.

[Indexed for MEDLINE]

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