Mask-applied continuous positive airway pressure (CPAP) has been shown to reduce morbidity among patients with acute respiratory distress in the setting of cardiogenic pulmonary edema. OBJECTIVE: To determine a minimum percentage of patients transported by ALS for difficulty breathing who could potentially benefit from a pre-hospital trial of CPAP. METHODS: Paramedic run sheets were collected from consecutive, adult, ALS transports for a chief complaint of difficulty breathing over a 6 week period in a large urban EMS system. Demographic information, medical history, vital signs, clinical assessments, and transport times were abstracted into a database by trained reviewers. Strict criteria for CPAP were defined in advance as "acute respiratory distress," meaning (1) respiratory rate > 25 and (2) labored or shallow breathing, and "presumed cardiogenic pulmonary edema," meaning (3) a prior history of heart disease and (4) presence of bilateral rales on exam. RESULTS: Data from 240 consecutive run sheets were compiled. Median patient age was 66 years old, with females outnumbering males 168 to 81. A total of 15 spontaneously breathing patients met all 4 criteria for CPAP. Four of these patients were either hypotensive (SBP < 90) or had potential for airway compromise (i.e., obtundation), making CPAP inadvisable. Among the 11 remaining patients (4.4% of all transports for difficult breathing), median transport time was 20 minutes (range 14-31 minutes). CONCLUSIONS: Using very strict criteria, a small but not significant percentage of patients are optimal candidates for a prehospital trial of CPAP. Transport times would appear to justify this type of intervention. A prospective study is currently under way to test the feasibility of administering CPAP to such patients in the prehospital setting.