Ethical statement
This study was approved by the Institutional Review Board of Kansai Medical University (approval date: May 28 3, 2018; approval number: 2017320). The requirement for informed consent was waived because of the retrospective nature of the study.
Study design and population
Spontaneous pneumothorax in patients who underwent initial management in the outpatient clinic or were admitted to our hospital between January 2006 and December 2015 were included and analysed in this retrospective, single-institutional study. Initial treatment was selected by each attending doctor. Patients with primary spontaneous pneumothorax (PSP) and secondary spontaneous pneumothorax (SSP) were included. SSP was defined as pneumothorax in patients with an obvious underlying lung disease or those older than 50 years of age. Patients of first and repeated episodes were included in this study.
Classification of lung collapse
Degree of lung collapse was categorised according to the chest radiographic appearance as low, middle, or high as per the definition proposed by The Japan Society for Pneumothorax and Cystic Lung Disease (JSPCLD) as follows: 1) low: apex is at the same level or higher than the clavicle, 2) high: total or almost total collapse, and 3) middle: the degree between low and high. High and middle degrees of lung collapse defined by JSPCLD are almost equivalent to large pneumothorax defined by the British Thoracic Society (BTS) and the American College of Chest Physician (ACCP) guidelines [3, 4], and low degree of pneumothorax to small pneumothorax.
Definition of terms
In this report, initial treatments denoted treatments firstly performed for pneumothorax and indicated the following three methods: observation, needle aspiration, or tube drainage. To evaluate efficacy of the initial treatment, “success” and “failure” were defined as follows. When initial treatment achieved lung re-expansion and no lung collapse in following observation, or did not show air leak, the treatment was evaluated as a “success.” When a patient did not achieve stable lung re-expansion, or showed persistent air leak after initial treatment, the treatment was considered as a “failure.” In failure of initial treatments, further treatments were performed to cease air leak. To evaluate success and failure, the durations required for each treatment was not specified in this study, because of retrospective analysis. In some of the successful cases, additional treatments were performed to prevent recurrence even after cessation of air leak. Further, additional treatments included surgery and chemical pleurodesis in addition to the three initial treatments. To evaluate recurrence, last treatment was analysed. When patients achieved success with initial treatment and did not undergo additional treatment for prevention of recurrence, the initial treatment was also counted as the last treatment. When patients needed further treatments to cease air leak after the initial treatment, the initial treatment was recorded as a failure, and the second or third treatment to finally cease air leak (without any additional treatment) was counted as the last treatment. When additional treatment was performed, the final one was counted as the last treatment. Recurrence on the ipsilateral side was only counted as recurrence.
Data collection
The following clinical data and radiological findings were collected from patients’ medical records and chest X-rays: age, sex, smoking history, previous episode of ipsilateral pneumothorax, side of pneumothorax, underlying lung disease, degree of lung collapse, radiological finding of bulla formation or pulmonary fibrosis, intervention for pneumothorax, and recurrence of pneumothorax. Information of the intervention from the initial management was collected along with the patient’s time line as follows: 1) initial treatments; 2) further treatments to cease air leak in cases of failure, including second and third treatments; and 3) additional treatments to prevent recurrence after cessation of air leak. Recurrence-free interval was defined as the period between the day of the last treatment and the day of recurrence. When the patient was managed by only observation and cured, recurrence-free interval was defined as the period of radiographically evaluated day between full expansion of the lung and the day of recurrence.
Statistical analysis
Analysis of treatment efficacy to manage air leaks was performed by initial treatment and that of recurrence was performed by last treatments. Continuous variables were reported as a mean with standard deviation, and categorical variables were expressed as number of patients. Statistical analysis was performed to investigate the risk factors for persistent air leak on initial treatment and those for recurrence of ipsilateral pneumothorax after the last treatment. The Wilcoxon rank-sum test and the Fisher exact test were used to compare continuous data and categorical data, respectively. Logistic regression analysis was used in univariate and multivariate analyses. Factors with a p-value < 0.2 in univariate analyses were used in multivariate analyses. A Cox proportional hazard model was used to estimate the recurrence risk. The cumulative recurrence rate was estimated by the Kaplan–Meier method. A p-value < 0.05 was considered statistically significant. All statistical analyses were performed using JMP software version 13.2.1 (SAS Institute, Inc., Cary, NC, USA).