Ambulances inherently raise the risk of collisions due to their increased mass requiring extra braking distance. Even when compared to vehicles of similar size, ambulance crashes occur more often at intersections, with 84 percent involving three or more people. Furthermore, the majority of EMS collisions occur when driving with L&S. A Denver study reported that L&S use accounted for 91 percent of all ambulance crashes.2
Obviously, the concern with unnecessary L&S use is the risk of injury to providers, patients, or pedestrians in a collision. However, there are other negative externalities as well. Studies suggest that L&S use increases patient stress and anxiety, which may result in increased catecholamine surge, heart rate, and blood pressure.2,4 In urban regions, “alarm fatigue” is a concern when drivers don’t clear the way for ambulances because they are too frequently confronted with emergency vehicles driving with L&S. If the frequency of L&S use decreased, limited to cases with the potential for real benefit, perhaps alarm fatigue would diminish. Finally, there is the recognition that L&S travel is just not that effective.
The Effectiveness of Lights and Sirens
The major indication for L&S is a presumed significant decrease in response and transport time. However, multiple studies reveal minimal decrease in transit time with L&S use, with an average of 1.7 to 3.6 minutes saved.5 In Greenville, North Carolina, the average reduction with L&S was 43.5 seconds. In congested, urban regions, there is not a marked difference with L&S either. In one urban study, L&S use resulted in a three-minute reduction in Minneapolis. In Washington D.C., there were 3.6 and 3.0 minute faster mean response and transport times with L&S use, respectively. Studies also show that the majority of patients agreed with the practice of non-L&S transport once evaluated by EMS.2
For most conditions, EMS providers can provide timely care on-site or en route to diminish the importance of time saved by L&S transport, thus reducing the risk to providers, patients, and public. In greater than 90 percent of patients, there is no improved outcome from L&S use.2 For some conditions, such as ST-elevation myocardial infarctions, trauma with life-threatening hemorrhage, obstetrical emergencies, or ischemic strokes, the use of L&S use may improve patient outcome by decreasing transit time. However accurate prehospital notifications to the receiving hospitals may be more beneficial than L&S as this should reduce in-hospital delays waiting for therapeutic interventions. In some cases, prehospital notification has shown an evidence-based improvement in patient outcome by mobilizing the necessary resources.2,6