WHEN DO MINUTES MATTER?
EMS agencies are feeling the strain
In recent years, agencies across the United States have seen EMS call volume rise while personnel and ambulance availability have fallen. That combination leaves systems facing a difficult decision: which calls to prioritize, which to defer, and which to refer to alternative care such as telemedicine or secondary nurse triage.
Most standardized dispatch response prioritization systems are designed to establish a call acuity and urgency on the assumption of an immediate response. Without other guiding data, many EMS systems are turning to dispatch acuity determinant levels to help decide response timing.
The study
Researchers from ESO and Johns Hopkins partnered with eight EMS agencies to look more closely at the relationship between the output of a widely used dispatch system and time-critical illness. The goal was to begin building a data-driven framework for informing 911 response prioritization.
All eight participating systems had dispatch centers accredited by the International Academies of Emergency Dispatch and used the Medical Priority Dispatch System (MPDS). The research team used MPDS dispatch protocols and determinant levels to evaluate time-critical intervention and hospital outcomes, reviewing 1.7 million incidents between January 1, 2021 and June 30, 2023.
How time-critical was defined
A multi-round survey went to each EMS agency to build consensus on time-critical EMS interventions and emergency department outcomes. Cardiac arrest after EMS arrival and patient death in the emergency department were predefined as time-critical and included automatically.
- Items identified by 75% or more of respondents in the first round were classified as time-critical immediately
- Items with 25% to 74% of votes went to a second round, with those receiving at least 50% included
- Items receiving 25% or fewer votes were excluded from the definition
The results
DELTA (critical) was the most common determinant level, making up 27% of calls, followed by CHARLIE (emergent) and ALPHA (low acuity) at around 25% each. OMEGA (non-acute), the least urgent, was least common at 2%.
Overall, time-critical EMS intervention or emergency department diagnosis increased alongside determinant level: as a call determinant level rose, more time-critical treatments and outcomes were documented.
| Determinant level | Time-critical EMS treatment | Time-critical ED outcome |
|---|---|---|
| OMEGA | 1% | 3% |
| ALPHA | 1% | 6% |
| BRAVO | 4% | 12% |
| CHARLIE | 7% | 14% |
| DELTA | 10% | 14% |
| ECHO | 38% | 31% |
There was, however, a small group of lower acuity determinant level protocols with a high proportion of time-critical intervention or outcomes. Seven of the 32 included ALPHA protocols, or 22%, had more than 10% of responses involving a time-critical EMS intervention or outcome.
Key takeaways
These findings may help inform prioritization frameworks. If a system set a threshold of under 1% time-critical EMS intervention and under 5% time-critical emergency department diagnosis, 8% of EMS requests could be safely referred to alternative resources or deferred for non-emergent dispatch.
At the same time, not all low acuity determinant levels are safe to hold: 22% of ALPHA protocols exceeded 10% time-critical treatment or outcome.
What can we learn from this?
The findings point to the need to weigh both the chief complaint and the acuity of dispatch, so the right calls are prioritized and matched with the right resource. Three recommendations follow:
Voices from participating agencies
“When multiple calls come in simultaneously, there’s a likelihood that some are from individuals facing more severe health crises. By prioritizing the sickest patients, we ensure that ambulance resources are allocated first where they’re needed most.”
Jeff Williams, Deputy Medical Director, Wake County Department of EMS
“This program has truly been a game-changer for us in Austin, especially during peak demand periods. Austin is a big hub for events, we often get an influx of out of towners, so it’s crucial to maintain our resources appropriately. By validating our data through ESO, we are confident that our expanded triage program aligns with the study findings.”
Heidi Abraham, MD, Chief Deputy Medical Director, Austin-Travis County EMS
The work is just getting started
Because only a small number of lower acuity determinant levels meet the criteria for being unsafe to hold, the industry needs ways to bring flexibility into how dispatch prioritization is determined, weighing both protocol and determinant level. More research is needed before we can fully optimize which responses to defer and which need immediate attention.
Our research partners
Thank you to the agencies whose participation made this project possible.
- Johns Hopkins University, Baltimore, MD
- Austin-Travis County EMS, Austin, TX
- Office of the Medical Director, Metropolitan Oklahoma City and Tulsa, OK
- Charleston County EMS, Charleston, SC
- Johnston County EMS, Smithfield, NC
- Guilford County EMS, Greensboro, NC
- Office of the Medical Director, Johnson County EMS System, Olathe, KS
- Lee County EMS, Fort Myers, FL
- Wake County EMS, Raleigh, NC
