Date: April 24th, 2020

ReferenceWatanabe et al. Is Use of Warning Lights and Sirens Associated With Increased Risk of Ambulance Crashes? A Contemporary Analysis Using National EMS Information System (NEMSIS) Data. Annals of Emergency Medicine. July 2019

Guest Skeptic: Dr. Robert Edmonds is an emergency physician in the US Air Force in Virginia.  This is Bob’s eleventh visit to the SGEM.

Disclaimer: The views and opinions of this podcast do not represent the United States Government or the US Air Force.

Case:You are visiting with your father, a 64-year-old overweight man with hypertension.  He describes significant pain in his chest upon awakening and tells you to call an ambulance.  The EMS crew arrives and performs a 3 lead EKG that does not show an ST elevated myocardial infarction. They prepare to load your father into the ambulance, and since you’re his only child and he’s a talker, he mentions you’re an emergency physician.  The crew then asks if you want them to transport your father Code 3 with full lights and sirens.

Background: The use of warning lights and sirens in ambulances is fairly widespread. Their use is associated with marginally faster response and transport times (7).

Several studies have found ambulance crashes occurring while lights and sirens are used to have a higher injury rate, and a majority of fatal ambulance crashes involve their use (12-15).

EMS agencies have varying guidelines on when to use lights and sirens, and the amount of time saved with lights and sirens is approximately 1-3 minutes (REF).  This means the intervention is likely unhelpful for the patient in many transports.

Clinical Question: What is the association between warning lights and sirens use by EMS and crash-related delays?

ReferenceWatanabe et al. Is Use of Warning Lights and Sirens Associated With Increased Risk of Ambulance Crashes? A Contemporary Analysis Using National EMS Information System (NEMSIS) Data. Annals of Emergency Medicine. July 2019

  • Population: All dispatches of a transport-capable ground EMS vehicle to a 911 emergency scene from the 2016 National EMS Information System, both the response to the scene and the transport from the scene.
    • Excluded: Interfacility transfers, intercepts, medical transports, and standbys; responses by nontransport or rescue vehicles, mutual aid activations, and supervisor responses; and events documented as responses or transports by rotor-wing or fixed-wing air-medical services.
  • Intervention: Use of lights and sirens
  • Comparison: No lights and sirens
  • Outcome: Crash-related delay (proxy for EMS vehicle crash)

Authors’ Conclusions: “Ambulance use of lights and sirens is associated with increased risk of ambulance crashes. The association is greatest during the transport phase. EMS providers should weigh these risks against any potential time savings associated with lights and sirens use.”

Quality Checklist for Observational Study:

  1. Did the study address a clearly focused issue? Yes
  2. Did the authors use an appropriate method to answer their question? Yes
  3. Was the cohort recruited in an acceptable way? Yes
  4. Was the exposure accurately measured to minimize bias? Yes
  5. Was the outcome accurately measured to minimize bias? Yes/No
  6. Have the authors identified all-important confounding factors? Yes
  7. Was the follow up of subjects complete enough? Yes
  8. How precise are the results/estimate of risk? Adequate
  9. Do you believe the results? Yes
  10. Can the results be applied to the local population? Yes
  11. Do the results of this study fit with other available evidence? Yes

Results: The 2016 NEMSIS database contained 20.4 million 911 dispatches of ground EMS. There was a total of 2,539 crash-related delays.

Key Result: There was a greater odds ratio of crashing with the use of lights and sirens.

1) Reporting Bias: The authors mention how the study is entirely dependent on crash related delays.  It is unknown how widespread reporting of crash-related delays is and since this is dependent on individual agencies self-reporting, there may be bias from the agencies to report this more commonly when lights and sirens are used, as this was already believed at the time of the study to induce additional risk.  Alternatively, as the authors point out, some upgrades to lights and sirens may occur after an ambulance crash has occurred, which would bias the results.

2) Association not Causation: It would not be correct to conclude that lights and sirens  cause crashes from this publication. This was a retrospective database study not a randomized controlled trial. There could have been unmeasured confounders responsible for the observed results.

3) Partial Lights and Sirens:The authors teased apart three scenarios-complete absence of lights and sirens, full use of lights and sirens, and partial use of lights and sirens. These partial use cases include both cases where there was initially no lights and sirens and then they upgraded to lights and sirens, as well as cases where the crew started with lights and sirens, and they downgraded, turning off the lights and sirens.  Due to the retrospective nature of this study, it’s not possible to discern at a systematic level how these upgrade and downgrade situations are determined and if there is a theme to these which would impact the results.

Sam Peltzman

4) Peltzman Effect: This is a theory that proposes people will be more likely to engage in risky behavior when safety measures have been introduced. This change in behaviour will compensate for any benefit achieved by intervention. It is named after Sam Peltzman who in the 1970’s hypothesized that mandating seatbelts in cars would increase risky behaviour and results in more crashes/injuries. His proposal was controversial and the data from seatbelts ultimately demonstrated a net benefit. However, there are a number of examples of the Peltzman effect

In medicine, there can also be unintended consequences of health care interventions (smoking cessation, electronic health records, rapid response teams, etc). When an intervention is introduced it can nudge behaviour of the physician and the patient resulting in compensatory responses that may have a net negative impact (Prasad and Jena 2014).

Lights and siren use by EMS may give the paramedics a false sense of security. They may drive more aggressively that results in a greater number of crashes.

5) Lack of Patient Oriented Outcomes: Although the direct comparison of lights and sirens and crashes is important, it would have been interesting if data could be collected on patient important outcomes, such as mortality, injuries to the patients or EMS crews, or duration of delays.

Comment on Authors’ Conclusion Compared to SGEM Conclusion: We agree with the authors that there is an associated increase in crashes with the use of lights and sirens, but this appears to be much less statistically compelling in the response phase.

SGEM Bottom Line: The use of warning lights and sirens was associated with a significant increase in the risk of crashing in the transport phase.

Case Resolution: You tell the EMS crew to use their best judgement, and they drive to the nearest emergency room without the use of lights and sirens. Your father is diagnosed with a pulmonary embolism and convalesces in the hospital for a few days until he is uneventfully discharged home on apixaban.

Dr. Robert Edmonds

Clinical Application: For clinicians involved in the decisions regarding EMS utilization, this study further focuses on the need for judicious use of lights and sirens.  As noted in the accompanying editorial by Tanaka in the same issue of Annals, “the Fire Department of the City of New York estimated a 32% reduction in crashes during their test period with updated lights and sirens protocols.” When this is coupled with the fairly minor reduction in transport time of only 1-3 minutes with the use of lights and sirens, it makes a strong case to limit the use of lights and sirens for only the patients with the direst need for timely emergency medical care.

What Do I Tell My Patient? The ambulance crew will make a choice about whether it’s appropriate to use lights and sirens to transport you to the hospital.  Even if they don’t go with lights and sirens, they’re still going to get you to the hospital quickly, and there’s less risk of crashing.

Keener Kontest: Last weeks’ winner was a repeat win for Jonathan Godfrey a paramedic from Asheville, NC. He knew the name of Dr. Boyles publication, in 1661, that bears directly on the SGEM is: “The Sceptical Chymist: or Chymico-Physical Doubts & Paradoxes”.

Listen to the SGEM podcast to hear this weeks’ question. Send your answer to with “keener” in the subject line. The first correct answer will receive a cool skeptical prize.

Remember to be skeptical of anything you learn, even if you heard it on the Skeptics’ Guide to Emergency Medicine.