Prehospital CPAP belongs in every EMS toolbox. (Photo/Adam Mason)

CPAP (Continuous Positive Airway Pressure) ranks as one of the most effective interventions in the EMS toolbox for improving patient outcomes. In fact, CPAP outranks all but two EMS interventions: taking a critically injured geriatric trauma patient to a Level 1 trauma center and administering benzodiazepines to a patient in status seizures.1 With readily available, single use, disposable prehospital CPAP devices, the weight of published evidence now suggests that not carrying CPAP, even at the BLS level, is inexcusable.

In earlier articles, we explored the history of CPAP (CPAP: From Beginning Until Now), its effects (The Miracle of CPAP), noting that, while every acutely dyspneic patient deserves a trial of CPAP, it most certainly is more effective for some conditions than others. Regardless, there remain administrators and medical directors who need convincing that prehospital CPAP is worth the education and expense. Interestingly, most of the published evidence demonstrating CPAP outcomes benefits are prehospital studies. On the hospital side, there is actually a dearth of research supporting use of CPAP for inpatients. 

One of the earliest studies of prehospital CPAP was done in Cincinnati, Ohio and published in 2001. Nineteen patients with suspected acute pulmonary edema, all in need of imminent intubation, were instead given a trial of CPAP. Their average SpO2 increased from 83.3% to 95.4%. None required intubation in the field; two were intubated in the ED and five intubated later during their hospital stay.

Most impressively, besides the fact that none were intubated in the field, their average hospital length of stay for these 19 acute pulmonary edema patients decreased from 11 to 3.5 days, likely because of the prehospital use of CPAP.2 This EMS study caught the attention of hospitals: a prehospital intervention resulting in a 68% reduction in hospital stay. Since hospitals are paid a fixed rate for each admitting diagnosis regardless of length of stay, they saw good reason to begin buying CPAP units for their local EMS services.

The evidence for prehospital CPAP continued to build.6-47 In considering the effectiveness of a medical intervention, whether prehospital or otherwise, we often use a statistical calculation called “number needed to treat,” or NNT. The NNT is the number of patients that need to be treated to avoid one outcome event. Sometimes that outcome is mortality (death), other times, it might be, as in the case of CPAP, intubation.

In the first paper recommending prehospital use of CPAP for patients with acute pulmonary edema, the NNT to prevent one patient from needing to be intubated was six. This means that use of CPAP on six patients was likely, on average, to result in one of those six from needing to be intubated. Compare that to an NNT of 15 to prevent one death using a bundle of aspirin, 12-lead, and direct transport to a STEMI center for acute MI.1

More recently, the prehospital NNT for use of CPAP in acute pulmonary edema has dropped to five to prevent one patient from being intubated and now has an NNT of 12 to prevent one death.3 This is powerful stuff. If you want to learn more about NNT, visit the website There, you will see wide variations in NNT. While the optimal NNT is one, meaning every single use of a procedure prevents an adverse outcome (i.e., improves the patient condition), that rarely happens. Typically, an NNT of 10 or less suggests the procedure is worthwhile.

Few EMS practices have such low NNTs. Spinal immobilization in penetrating trauma patients, for example, showed no benefit to any patients but had a “Number Needed to Harm” or NNH of 10, meaning that for every 10 penetrating trauma patients that were treated with prehospital spinal immobilization, one died.4 Use of video laryngoscopy instead of conventional (direct) laryngoscopy has an NNT of 14 for preventing failed intubation and an NNT of 11 for preventing post intubation hoarseness.5

In the many references provided at the end of this article, we can glean substantial prehospital CPAP outcomes benefits. Make note, especially for those who believe their transport times are too short to warrant use of CPAP: every single patient outcome benefit improves the earlier CPAP is applied. Waiting until arrival at the ED, in many studies, practically eliminated any benefits. Here is a synopsis of what we understand the potential outcomes benefits of prehospital CPAP are in 2020:

  1. Decreases need for intubation by up to 48%. This is no small effect when you consider the potential complications of endotracheal intubation such as aspiration, misplaced ET tubes, vocal cord injury, barotrauma, and ventilator acquired pneumonia, to name a few.
  2. Decreased hospital length of stay by as much as two-thirds. While the cost savings here would seem to accrue to hospitals, the more efficient bed turnover has a palpable downstream effect for EMS in reducing crowding and perhaps shortening wait times in Emergency Departments because of the increased availability of beds.
  3. Decreased overall complications by up to 32%. This includes all complications both prehospital and in-hospital. Complications, all of which have potential to adversely affect patient outcomes include medication errors, central line associated blood infections (CLABIs), catheter association urinary tract infections (CAUTIs), falls, and virtually any other complication you can imagine.
  4. Decreased in-hospital mortality by more than 20%. This represents not just mortality from respiratory or cardiac conditions that initially resulted in the need for CPAP, but all-cause mortality.

When you consider the evidence we currently have for improved outcomes from use of prehospital CPAP, the numbers demonstrate that a small service treating 30 patients over a one-year period with CPAP could easily have prevented five people in their community from needing to be intubated, saved tens of thousands of dollars in hospital costs, prevented hundreds of patient complications and likely saved three patients from dying. Given the overwhelming evidence of improved outcomes, prehospital CPAP belongs in every EMS toolbox.


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Mike McEvoy, PhD, NRP, RN, CCRN, is the EMS coordinator for Saratoga County, New York, and the professional development coordinator for Clifton Park and Halfmoon Ambulance. He is a nurse clinician in the adult and pediatric cardiac surgery intensive care units at Albany Medical Center, where he also teaches critical care medicine. McEvoy is the chief medical officer and firefighter/paramedic for West Crescent Fire Department in Clifton, New York. He is also the chair of the EMS Section board of directors for the International Association of Fire Chiefs and a member of the New York State Governor’s EMS Advisory Council. He is a lead author of the textbook Critical Care Transport, the “Informed” Pocket References (Jones & Bartlett), and the American Academy of Pediatrics textbook Pediatric Education for Prehospital Professionals (PEPP).

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