Additionally, the acoustic aspects of siren effectiveness have been studied in detail.2 Source characteristics such as level, frequency, and directionality, and temporal propagation characteristics such as geometric spreading, atmospheric absorption, topography effects, and background noise are all important components. A 1978 study’s conclusion, reaffirmed in a 2012 study, found that siren warnings were only effective when vehicles were traveling in the same direction ahead of the emergency vehicle, when a vehicle was weaving through dense, stationary traffic, or to pedestrians.2 It is clear that sirens may not be as effective as providers may assume and thus cannot be relied on to clear the way.
One retrospective study found that only 5 percent of patients benefit from the time saved by L&S.7 EMS medical directors should focus the training and preparation of EMS providers to provide appropriate medical interventions and to provide accurate and reliable prehospital notifications. Medical directors and operational supervisors for EMS agencies should conduct quality assurance initiatives to ensure a constant assessment of L&S utilization and its effects on patient outcomes.
Emergency Medical Dispatch Risk Stratification
Emergency medical dispatch (EMD) risk stratify 911 calls and initiate a non-L&S response based upon a structured call-taking process, a concept first pioneered by Dr. Jeff Clawson in 1982. In the same year that Salt Lake City instituted an EMD policy to risk stratify calls and identify time-dependent emergencies, they decreased the L&S response by 50 percent. The same year there was a 78 percent reduction in emergency vehicle collisions.2,9
Variability of L&S Use Nationwide
The recognition of safety risks associated with L&S has initiated a change in EMS safety culture. Between 2010 and 2015, the rate of L&S use during patient transport decreased. However, the rate of L&S use when responding to the scene was constant. There is significant variability in the utilization of L&S throughout the country for both response and transport. For example, rural and urban areas are more likely to use L&S compared to suburban regions. Such variable utilization of L&S is likely influenced by EMS agency policies, municipal contracts, traditions within agencies, driver training, and medical oversight.2
It is unfortunately common for municipal contracts to require EMS response within eight minutes of dispatch with financial ramifications if the time requirement is not met. In 2015, the EMS agencies in Tulsa and Oklahoma City changed the response policy in order to reduce L&S use to 33 percent of its responses.2 It shifted focus to patient outcomes and quality of care as more important metrics than response time. Importantly, after reduction in L&S rates, there was no associated increased morbidity or change in their cardiac arrest survival rate.2 Additionally, Merlin and colleagues developed a simple medical protocol for L&S transport which reduced an urban EMS agency from 50 percent to 29 percent for patients transported by advanced life support providers.8