Prehospital Lung Ultrasound in Acute Heart Failure: Impact on Diagnosis and Treatment

Abstract

Background and Objectives Patients with acute heart failure (AHF) are commonly misdiagnosed and undertreated in the prehospital setting. These delays in diagnosis and treatment have a direct negative impact on patient outcomes. The goal of this study was to determine the diagnostic accuracy of AHF by paramedics with and without lung ultrasound (LUS). We also assessed LUS impact on rate of initiation and time to initiation of HF therapies in AHF patients with and without LUS performed.

Methods This was a prospective, nonrandomized, interventional study on a consecutive sample of patients transported to the hospital by one emergency medical services agency. Adult patients (>18) with a chief complaint of dyspnea and at least one of the following: bilateral lower extremity edema, orthopnea, wheezing or rales on auscultation, respiratory rate >20 or oxygen saturation < 92% were included. LUS was performed when a paramedic trained in LUS was present and an US was available on the ambulance. LUS was defined as positive for AHF if both anterior-superior lung zones had >2 B-lines or bilateral B-lines were visualized on a 4-view protocol. Paramedic diagnosis with and without the use of LUS was compared to hospital discharge diagnosis using Fishers exact analysis. Kappa was used to determine LUS interpretation interrater reliability between paramedic and expert. HF therapy was defined as nitroglycerin prehospital and furosemide in the emergency department. Time to treatment was defined as paramedic initial patient contact time to the time treatment was administered.

Results A total of 353 patients were enrolled from March to September 2022; 89 did not meet inclusion criteria. Of the 264 included patients 94 (35%) had AHF. Forty patients had a LUS performed. Sensitivity and specificity for AHF by paramedics was 23% (95% CI 0.14-0.34) and 97% (CI 0.92-0.99) without LUS and 71% (95% CI 0.44-0.88) and 96% (95% CI 0.76-0.99) with the use of LUS. In the 94 patients with AHF, 14% (11/77) received HF therapy prehospital without the use of LUS and 53% (9/17) with the use of LUS. LUS improved frequency of treatment by 39%. Median time to treatment was 19 minutes with LUS and 149 minutes without. Kappa for LUS interpretation was 0.79 (CI 0.6-0.98).

Conclusion LUS improved paramedic sensitivity and accuracy for diagnosing AHF in the prehospital setting. LUS use led to higher rates of prehospital HF therapy initiation and significantly decreased time to treatment.