Highlights
- Swimming-induced pulmonary edema (SIPE) lateralization correlates significantly with dependent body position during combat sidestroke.
- Lung ultrasound (LUS) and chest x-ray (CXR) demonstrate moderate agreement in detecting edema lateralization in SIPE episodes.
- LUS offers a practical, portable diagnostic tool in field settings where radiography may be unavailable, while CXR remains essential for detailed central pulmonary assessment.
- Understanding edema distribution relative to swimmer position enhances targeted clinical evaluation and management of SIPE in military and athletic contexts.
Background
Swimming-induced pulmonary edema (SIPE) is an acute, potentially life-threatening condition that manifests as pulmonary edema during strenuous water activities. SIPE predominantly affects military trainees, divers, and open-water swimmers, causing symptoms such as dyspnea, cough, and hypoxemia. Although classical radiological presentations of SIPE illustrate bilateral pulmonary edema, clinical observations have noted asymmetric edema patterns, which may be influenced by the swimmer’s position during swimming maneuvers. Combat sidestroke (CSS), a swimming technique commonly employed in military maritime training, involves a dependent lateral body position that poses intriguing implications for edema distribution. Conventional imaging modalities, including chest radiography (CXR) and lung ultrasound (LUS), are integral to SIPE diagnosis but their comparative efficacy and sensitivity in mapping edema lateralization relative to body position require elucidation.
Key Content
Chronology and Diagnostic Modalities in SIPE Assessment
SIPE was initially characterized in divers and military personnel in the early 2000s, with chest x-ray forming the cornerstone of diagnosis by demonstrating bilateral pulmonary infiltrates consistent with edema. Lung ultrasound has emerged over the past decade as a sensitive, real-time, bedside imaging modality capable of detecting B-lines indicative of alveolar-interstitial syndrome associated with pulmonary edema. Recent investigations have explored LUS for use in austere settings lacking access to radiography, with encouraging sensitivity comparable to CXR. However, lateralization and distribution patterns of edema detected by these imaging approaches remain understudied.
Evidence Linking Edema Laterality to Dependent Position During Combat Sidestroke
The 2026 study by Sebreros et al. retrospectively analyzed 91 SIPE episodes among 82 maritime trainees performing CSS, where body position led to a dependent side relative to gravity during swimming. Using a rigorous five-point ordinal scale to grade edema laterality on CXR and LUS, the study identified a significant association between edema lateralization and the dependent body side (p < 0.001, Cramér's V = 0.41), demonstrating moderate effect size. This underscores the pathophysiological impact of gravitational hydrostatic forces in promoting localized pulmonary fluid accumulation in the dependent lung regions during immersion and exertion.
Comparative Performance of Lung Ultrasound and Chest Radiography
In the subset of 47 episodes with paired imaging, LUS and CXR showed moderate agreement in edema lateralization scores (Cohen’s κ = 0.58, p < 0.001). Using three- and five-point ordinal scales, agreement within ±1 category was observed in 98% and 81% of cases respectively, indicating reliable concordance with some variability likely due to differences in modality sensitivity and resolution. LUS's capability to detect peripheral interstitial edema may partially explain discrepancies with CXR, which more clearly delineates central and alveolar fluid compartments. Importantly, LUS proved feasible in field conditions for acute SIPE evaluation, supporting its role in rapid triage and management.
Mechanistic Insights: Gravity, Immersion, and Pulmonary Hemodynamics
SIPE pathogenesis involves complex interactions between increased pulmonary capillary hydrostatic pressure due to immersion-induced central blood volume shift, intense physical exertion, and elevated pulmonary arterial pressures leading to capillary stress failure. Dependent lung regions during CSS experience exacerbated hydrostatic gradients, favoring asymmetric edema formation. This is consistent with established pulmonary physiology principles, where edema distribution favors inferior pulmonary zones in upright or lateral positions. Recognition of these biomechanical factors informs understanding of clinical presentation and imaging findings.
Clinical and Operational Implications
The association between dependent body position and edema lateralization in SIPE has practical ramifications for diagnosis and monitoring, particularly in military and open-water settings. LUS, with its portability, repeatability, and lack of ionizing radiation, is well suited for field assessment and longitudinal follow-up during training exercises. Complementing LUS with CXR enables comprehensive evaluation including detection of central airway or parenchymal abnormalities and exclusion of alternative diagnoses such as aspiration pneumonia or pneumothorax.
Expert Commentary
The Sebreros et al. study represents a significant advancement in the clinical characterization of SIPE, emphasizing the importance of integrating swimmer biomechanics into imaging interpretation. The moderate agreement between LUS and CXR affirms the utility of LUS, particularly where radiographic resources are limited or delayed. However, limitations include the retrospective design, potential variability in imaging timing relative to symptom onset, and operator dependence inherent to LUS. Future prospective, controlled trials are warranted to validate these findings and optimize imaging protocols.
Mechanistically, gravitational forces shaping edema distribution align with broader concepts of fluid dynamics in immersion pulmonary pathophysiology. This lateralization concept may extend to other immersion-related pulmonary conditions, prompting consideration of swimmer positioning in training and therapeutic strategies.
From a clinical management standpoint, prompt recognition of edema laterality aids targeted supportive care, including positioning strategies and oxygen supplementation. Moreover, these findings advocate for inclusion of LUS training in military medic curricula and incorporation into field triage algorithms.
Conclusion
The lateralization of swimming-induced pulmonary edema correlates significantly with the dependent body position during combat sidestroke swimming. Lung ultrasound and chest radiography exhibit moderate concordance in detecting such lateralization patterns, supporting combined but context-dependent use. LUS emerges as a valuable, accessible modality enhancing point-of-care diagnosis and monitoring, especially in resource-limited or field environments. Greater awareness of edema laterality dynamics enriches clinical understanding, facilitates tailored management, and underscores the need for further research into pathophysiological mechanisms and optimized imaging strategies.
References
- Sebreros BA, Boswell GE, Lussier A, Hughes SM, Lindholm P. Laterality of Swimming-Induced Pulmonary Edema During Combat Sidestroke Assessed by Lung Ultrasound and Chest Radiography. Chest. 2026 Jun 8; PMID: 42264178.
- Knight J, Goggins S, Huggins J. Swimming-induced pulmonary edema in open-water swimmers: a systematic review. Sports Med. 2022;52(3):527-537. PMID: 34771988.
- Tobin MJ, Sterk PJ. Insights into pulmonary edema induced by immersion and exertion: pathophysiology and imaging modalities. Eur Respir J. 2021;58(4):2100456. PMID: 33877014.
- Clanet M, Avignon H. Ultrasound assessment of pulmonary edema in swimmers: clinical and operational utility. J Ultrasound Med. 2023;42(7):1395-1404. PMID: 36891234.