UC San Diego

BACKGROUND: Swimming-induced pulmonary edema (SIPE) causes acute respiratory symptoms during strenuous water activities and has been described in military trainees and open-water swimmers. Although SIPE typically presents bilaterally, asymmetric cases may relate to swimmer position. Chest x-ray (CXR) and lung ultrasound (LUS) are used in the clinical evaluation of SIPE, but whether they show similar edema lateralization patterns relative to swimmer position is unclear. RESEARCH QUESTIONS: Is edema laterality in SIPE associated with dependent body position during combat sidestroke (CSS)? When CXR and LUS are obtained during the same SIPE episode, do they show similar edema lateralization patterns? STUDY DESIGN AND METHODS: We retrospectively analyzed 91 SIPE episodes in 82 maritime trainees. Clinical records, CXR, and LUS were reviewed to characterize edema laterality on a five-point ordinal scale. Agreement between CXR and LUS laterality scores was assessed with Cohen's weighted kappa. Associations between imaging laterality and dependent body position during CSS were evaluated using Fisher's exact test, with Cramér's V to quantify effect size. RESULTS: Imaging data were available for 89 episodes with CXR, 49 with LUS, and 47 with both. Pulmonary edema laterality was significantly associated with dependent body position for both modalities (p < 0.001; Cramér's V = 0.41). CXR and LUS showed moderate agreement (κ = 0.58, p < 0.001) using three- and five-point scales, with agreement within ± 1 category in 98% and 81% of paired comparisons, respectively. INTERPRETATION: Among trainees who developed SIPE while performing CSS, edema laterality corresponded with the swimmer's dependent body position. CXR and LUS showed similar lateralization patterns with moderate agreement when obtained during the same SIPE episode. These findings support LUS as a practical tool in field settings for characterizing edema distribution when radiography is unavailable, while CXR remains important for evaluating central abnormalities and alternative pulmonary diagnoses.