LAUSR

BACKGROUND Despite increasing popularity of open water swimming worldwide, swimming induced pulmonary edema (SIPE) is a poorly recognized condition lacking established diagnostic criteria. RESEARCH QUESTION To determine diagnostic criteria of SIPE during a large open water swimming event. STUDY DESIGN Cross-sectional study METHODS: In total 17,904 individuals swam 1000, 1500 or 3000 m in cold open water during Sweden's largest open water swimming event in 2018 and 2019. Out of 166 swimmers seeking medical attention for acute respiratory symptoms, 160 were included in the study. Medical history, symptoms and clinical findings were collected. On-site lung ultrasound (LUS) was performed to verify pulmonary edema. RESULTS Pulmonary edema was confirmed by LUS in 102 patients (64%), of which 11 (7%) were unilateral. Peripheral oxygen saturation was identified as a strong independent diagnostic test for pulmonary edema, with ≤ 95% as suggested cutoff (Receiver Operator Characteristic Curve (ROC) curve; AUC 0.893, p<0.0001). Crackles on lung auscultation, predominantly over the anterior chest, identified 88% of patients with edema. Peripheral oxygen saturation ≤95% or auscultation findings of crackles identified pulmonary edema with a sensitivity of 97% and specificity of 86%. A specificity of 98% and a positive predictive value of 99% for LUS-verified pulmonary edema was reached if patients presented with both oxygen saturation ≤95% and auscultation of crackles. INTERPRETATION We suggest a clinical algorithm for diagnosis of SIPE for swimmers with acute respiratory symptoms during swimming in cold open water. Novel features of focally distributed edema in the anterior parts of the lungs, sometimes unilateral, add to this unique dataset of an underreported condition.