Discussion
Spontaneous pneumothorax is believed to be caused by the rupture of alveoli, although the precise cause is unknown. It may be a direct rupture or via the mediastinum4. In secondary spontaneous pneumothorax, weakness of the alveoli due to emphysema or necrotic pneumonia can be a cause of pneumothorax5. Acute respiratory distress syndrome is also a cause of secondary pneumothorax6 in addition to mechanical ventilation. Among COVID-19 patients, 1%-2% had pneumothorax7,8. Zantah reported six patients with pneumothorax, and four of them were under mechanical ventilation9. Martinelli reported 38 patients with invasive ventilatory support among 71 patients with pneumothorax10.
At our institute, the incidence of pneumothorax was 0.75% (8/1061). Patients in this hospital were not ventilated in principle because of divided hospital function in moderately ill patients, as per the policy of the prefectural government. We did not use NPPV for infection control. None of the patients with pneumothorax used HFNC; therefore, we can exclude the influence of barotrauma. Alternatively, the main cause of the pneumothorax could be alveolar weakness, as all patients except one young woman were over 80 years of age, and due to the high rate of steroid use (75%) and alveolar injury due to pneumonia. The limitation of this study is the small number of patients with pneumothorax in single institution, due to which we could not identify the risk factors of pneumothorax.
In acute Middle East respiratory syndrome, pneumothorax is associated with a poor prognosis11. Martinelli et al. reported that the mortality rate of COVID-19 was significantly higher in patients over 70 years of age than in those < 70 years of age10. At our institute, the overall mortality was 7.26% (77/1061), and that of patients over 80 years of age was 18.3% (61/334). The mortality rate of patients with pneumothorax over 80 years of age was as high as 85.7% (6/7). In conclusion, although pneumothorax is a rare complication, it can be a predictive factor of poor prognosis in elderly patients with COVID-19. Further studies including autopsy is required to clarify the relation between pneumothorax, COVID- 19, and underlying diseases.
Acknowledgements
We are grateful to Mr. Kenta Ebisawa who managed this temporary field hospital, and all past and present workers.
Disclosure
Approval of the research protocol: This retrospective study was approved by the ethics committee of Shonan Kamakura General Hospital.
Informed consent: The requirement for obtaining informed consent from patients was waived due to the retrospective nature of the study. Patients were allowed to withdraw from the study whenever they wished.
Registry and the registration no. of the study: N/A
Animal studies: N/A
Conflict of interest: None
Author Contributions: JK contributed to writing article; HK, YA, TK, HY, and SH contributed to conception and revision of article; CI, RS, NI, KM, TM, TN, YS, and YI contributed to data collection and patient care; and RF and HK contributed to manuscript review.
Data Sharing and Data Accessibility:
The data that support the findings of this study are available from the corresponding author upon reasonable request.
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Table 1 Clinical features of pneumothorax patients in coronavirus disease