Swimming-Induced Pulmonary Edema in a Member Participating in a Special Tactics Selection Course

CASE REPORT

A 28-yr-old healthy male candidate for becoming a U.S. Air Force Special Tactics Officer (STO) began experiencing severe shortness of breath during an early morning pool exercise on day 2 of the STO selection week. He was removed from the pool after the rescue swimmer observed the patient surface, gasping for air. On-site medical providers noted oxygen saturation (S_po₂) of 88 and placed the patient on 15-L supplemental oxygen via nonrebreathing mask. When his oxygen saturation did not improve after 15 min, the patient was taken to an on-site medical examination room while continuing supplemental oxygen. After climbing up one flight of stairs, his oxygen saturation dropped to 80, then slowly improved to 92 over the next 30 min. On lung auscultation, rales were present bilaterally. The patient had normal work of breathing and a mild cough with no sputum production. He denied aspiration of water. Due to his persistent hypoxia, the patient was transported to an emergency department 45 min away. On arrival, he was saturating at 100% after having been on oxygen via nonrebreather mask along with over 2 h of rest. He was taken off supplemental oxygen and maintained 99% S_po₂. He received a two-view chest X-ray, showing bibasilar pulmonary opacities, with lack of evidence of cardiomegaly or pneumothorax (Fig. 1 and Fig. 2). The patient desired to continue the selection course and was discharged from the emergency department (ED). He successfully completed the remaining physical exercises in the course, and at his follow-up 1 d after his ED visit, he had normal vital signs and felt well.

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DISCUSSION

The pathophysiology of SIPE is believed to be noncardiogenic and due to redistribution of blood from the extremities to the core, exacerbated by colder water temperatures. The central veins, heart, and pulmonary vessels fill with blood and increase right-sided intravascular pressures.⁴ Individuals at increased risk of SIPE have higher mean pulmonary artery pressures (MPAP) and pulmonary artery wedge pressures (PAWP) during exercise in cold water. Increased PAWP or MPAP may cause hydrostatic alveolar edema, as normal pulmonary capillary pressure has a value between MPAP and PAWP.^4,5 Based on these findings, risk factors for SIPE may include: higher blood volume, higher venous tone, impaired left ventricular systolic function, and low diastolic left ventricular compliance.⁴ Although asthma may worsen symptoms of SIPE, there is no evidence that SIPE involves bronchial hyperreactivity.⁶ SIPE does not involve an inflammatory process.⁵

Previous case reports and case studies on SIPE feature patients scuba diving, surface swimming (especially distance and triathlon swimming), cold water swimming, rescue swimming, aqua jogging, and training to become a U.S. Navy SEAL.¹ Risk factors are believed to include cold water, hypertension, female sex, long distance swimming, lower initial lung volumes, higher MPAP and PAWP, and lower tidal volumes.⁷ The patient did not have any known risk factors other than prolonged training in cold water.

One study found that having asthma was independently associated with both a longer duration of SIPE symptoms and a higher risk of SIPE recurrence.⁶ However, most studies describing SIPE are of healthy athletes and military trainees.^6,7 The most common symptoms are dyspnea and cough, although others include chest pain, chest tightness, tachypnea, hemoptysis, and altered mental status due to hypoxemia.¹ A suggested algorithm for diagnosing SIPE includes using pulse oximetry, with a cutoff of 95%, as well as lung ultrasound when SIPE is suspected, but the patient’s S_po₂ is above 95% or lung auscultation is clear without crackles.⁸ The presence of B-lines on lung ultrasound is indicative of pulmonary edema (Fig. 3).

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Treatment for SIPE includes supplemental oxygen, diuretics, beta-2 agonists, and noninvasive positive-pressure ventilation,⁹ in addition to patient rewarming and rest. A 2022 study concluded that noninvasive positive-pressure ventilation was a safe and effective prehospital treatment for SIPE. Some studies recommend treating SIPE with the same therapies used for other forms of noncardiogenic pulmonary edema, including mechanical ventilation if necessary.¹⁰ Further research into the efficacy of pharmacotherapy is needed, and not all patients with SIPE require more than supplemental oxygen before recovering, as in this case.

Although many articles describing SIPE state that symptoms usually resolve within 24–48 h, a long-term follow-up study on SIPE found that many patients reported symptoms lasting longer than 2 d, and over 20% of patients had symptoms lasting over 5.⁶ Recurrence of SIPE symptoms during open water swimming was found in 28% of participants, and many SIPE patients did not attempt open water swimming again during the study period. Patients reported that a SIPE diagnosis did not affect their physical activity levels.⁶ The risk of recurrence of SIPE may influence whether military trainees are allowed to continue performing jobs with open water swimming or diving duties, though SIPE is thought to resolve after several days and does not seem to affect physical fitness. In our case, the patient was able to return to the STO selection course and complete the remainder of physical activities successfully.

Though SIPE may affect a small percentage of swimmers, military training in extreme conditions such as cold, lack of sleep, and profound exertion increases the risk for SIPE. Additionally, a patient who develops SIPE in the water is at risk for drowning. As SIPE may be fatal, military providers, especially those working with Special Operations such as in Air Force Special Tactics or Navy SEALS, must be aware of how to diagnose and treat SIPE. Knowledge of SIPE is also important for ED providers who may continue providing care to these patients. It is easy to underestimate disease in a healthy patient such as a military trainee, but SIPE often affects previously healthy athletes, such as the patient described in this case. These patients typically recover quickly; however, they occasionally require early identification and treatment by knowledgeable providers to prevent more serious sequelae. SIPE should be in the differential of any provider covering water-based training or recreational events, even if athletes are in warmer water or swimming short distances in a pool.