Abstract
BACKGROUND: Current understanding indicates that primary spontaneous pneumothorax (PSP) typically occurs in younger individuals, whereas secondary spontaneous pneumothorax (SSP) is more common in older patients. However, the specific age distribution patterns distinguishing these two types of spontaneous pneumothorax (SP) remain poorly characterized. Furthermore, while a low partial pressure of oxygen (PaO₂) is a recognized clinical feature of pneumothorax, limited research has explored whether lower PaO₂ levels are specifically indicative of underlying lung disease in patients with SSP. METHODS: In this observational cohort study, we enrolled 473 male SP patients over a six-year period. We use frequency distribution plots to observe the distribution differences of continuous variables between SSP and PSP patients. Receiver operating characteristic (ROC) curve analysis and logistic regression modeling were employed to quantify the association between age, PaO₂, and SSP. RESULTS: The frequency distributions of age and PaO₂ were bimodal in patients with PSP and SSP. Multivariate logistic regression analysis identified age (using a cutoff of > 50 vs. ≤50 years) and PaO₂ (using a cutoff of > 90 vs. ≤90 mmHg) as independent factors associated with SSP, with odds ratios (ORs) of 10.58 (95% CI: 6.15-18.20) and 0.45 (95% CI: 0.27-0.74), respectively. While alternative cutoffs of age (> 40 vs. ≤40 years) and PaO₂ (> 85 vs. ≤85 mmHg) were also significant, with ORs of 7.74 (95% CI: 4.46-13.41) and 0.32 (95% CI: 0.19-0.55), the OR for age was lower (a decrease of 2.84 from the > 50-year cutoff). ROC curve analysis showed that the sensitivity and specificity for distinguishing SSP were 0.835 (95%CI: 0.812-0.853) and 0.789 (95%CI: 0.779-0.801), respectively, for the 50-year age cutoff, and 0.746 (95% CI: 0.721-0.762) and 0.679 (95%CI: 0.652-0.698) for the 90 mmHg PaO₂ cutoff. CONCLUSION: Among male patients with SP, an age of 50 years offers higher sensitivity and specificity than an age of 40 years in distinguishing SSP from PSP. Furthermore, even after oxygen administration, PaO₂ levels in SSP patients remain lower than those in PSP patients. A PaO₂ threshold of 90 mmHg also demonstrates high sensitivity and specificity in differentiating SSP from PSP.