To Örebro University

BACKGROUND: Swimming-induced pulmonary edema (SIPE) has been reported to subside within 24-48 hours, but comprehensive follow-up studies on symptom duration and long-term effects are missing.

RESEARCH QUESTION: What is the symptom duration, recurrence, and long-term effects of SIPE?

STUDY DESIGN AND METHODS: A follow-up study was conducted based on 165 cases of SIPE from Sweden's largest open water swimming event with 26,125 individuals participating during 2017-2019. Data on patient characteristics, clinical findings and symptoms were collected upon admission. Telephone interviews at 10 days and 30 months were performed to explore symptom duration, recurrence of SIPE symptoms, need of medical evaluation and long-term effects of self-assessed general health and physical activity level.

RESULTS: Follow-up at 10 days was performed for 132 cases and at 30 months for 152 cases. Most of the cases were women and mean age was 48 years. At the 10-day follow-up, symptom duration >2 days after the swimming race were reported by 38%. The most common symptoms were dyspnea and cough. In patients followed for 30 months, recurrence of respiratory symptoms during open water swimming was reported by 28%. In multivariable logistic regression, asthma was independently associated with both symptom duration >2 days and recurrence of SIPE symptoms (p =0.045 and p =0.022 respectively). Most participants reported equal or improved general health (93%) and physical activity level (85%) after experiencing SIPE, but 58% had not swum in open water since the event.

INTERPRETATION: The present large cohort study challenges the established hallmark of SIPE symptom duration of <48 hours, while SIPE recurrence was in the previously reported range. At 30 months, most patients reported unchanged self-assessed general health and physical activity level. These findings add to our understanding of the course of SIPE and can provide evidence-based information to swimmers and health care professionals.

BACKGROUND: Swimming-induced pulmonary edema (SIPE) occasionally occurs during swimming in cold open water. While optimal treatment for SIPE is unknown, non-invasive positive pressure ventilation (NPPV) is an option for prehospital treatment.

RESEARCH QUESTION: Is NPPV a feasible and safe prehospital treatment for SIPE, and which outcome measures reflect recovery after treatment?

STUDY DESIGN AND METHODS: A prospective observational study was conducted at Vansbrosimningen, Sweden's largest open water swimming event, in 2017-2019. Swimmers diagnosed with SIPE and with peripheral oxygen saturation (SpO₂) ≤95% and/or persistent respiratory symptoms were eligible for the study. NPPV was administered on-site as continuous positive airway pressure (CPAP) by facial mask or as positive expiratory pressure device (PEP-device). Discharge criteria were SpO₂ >95% and clinical recovery. Four outcome measures were evaluated: SpO₂, crackles on pulmonary auscultation, pulmonary edema on lung ultrasound (LUS) and patient-reported respiratory symptoms.

RESULTS: Of 119 treated individuals, 94 received CPAP, 24 PEP-device and one required tracheal intubation. In total, 108 (91%) individuals were discharged after NPPV for median 10-20 minutes, 11 (9%) required hospital transfer. NPPV resulted in increased SpO₂ from median 91% to 97% (p<0.0001) together with improvement of six patient-reported respiratory symptoms (median numerical rating scales 1-7 to 0-1; p<0.0001). No significant decrease in auscultation of crackles (93% vs 87%, p=0.508) or pulmonary edema on LUS (100% vs 97%, p=0.500) was seen during NPPV-treatment.

INTERPRETATION: NPPV administered as CPAP or PEP-device proved feasible and safe as prehospital treatment for SIPE with a vast majority of patients discharged on-site. SpO₂ and patient-reported respiratory symptoms reflected recovery after treatment, whereas pulmonary auscultation or LUS did not.

BACKGROUND: Despite increasing awareness of swimming-induced pulmonary edema (SIPE), there is a lack of large population-based studies and the incidence is unknown.

RESEARCH QUESTION: What is the incidence of SIPE in a mixed group of competitive and recreational swimmers during a large open water swimming event?

METHODS: In four consecutive years (2016-2019), a prospective cohort study was conducted during Sweden's largest open water swimming event - Vansbrosimningen. All swimmers seeking medical care with acute respiratory symptoms were eligible for the study. SIPE diagnosis was based on clinical findings in 2016-2017 and pulmonary edema assessed by lung ultrasound in 2018-2019. Data on patient characteristics, clinical findings and information about the race were collected.

RESULTS: Based on 47 573 consecutive swimming distances, 322 cases of acute respiratory symptoms (0.68%; C.I. 0.61%-0.75%) were presented at the mobile medical unit. Of these, 211 (0.44%; C.I. 0.39%-0.51%) were diagnosed with SIPE. The annual incidence of SIPE was 0.34%, 0.47%, 0.41% and 0.57%, respectively in 2016-2019. A majority of patients diagnosed with SIPE were women (90%) despite about equal percentage of men and women participating (47% men; 53% women). The incidence of SIPE was overall 0.75% in women and 0.09% in men. The incidence increased with age, from 0.08% in the youngest age group (18-30 years) to 1.1% in the oldest age group (≥61 years). Based on multiple logistic regression analysis, the adjusted odds for acquiring SIPE was 8.59 times higher for women compared to men and 12.74 times higher for the oldest age group compared to the youngest.

INTERPRETATION: The incidence of SIPE over four years during a large open water swimming event in Sweden was 0.44%. The incidence was higher in women than in men and increased with higher age.