Prevalence of hyponatremia and its association with respiratory failure in lung cancer patients admitted through emergency room

BACKGROUND: Hyponatremia and respiratory failure are common in cancer patients, but their relationship among lung cancer patients remains unclear. This study aimed to determine the prevalence of hyponatremia and its association with respiratory failure on admission among lung cancer patients presenting to the emergency room (ER). METHODS: This cross-sectional study was conducted between July 1, 2023, and June 30, 2024, in the ER of Persahabatan Hospital. Adults with histopathologically confirmed or previously established, untreated lung cancer were consecutively enrolled. Hyponatremia was defined as serum sodium <135 mmol/L, and respiratory failure as PaO 2 <60 mmHg or PaCO 2 >45 mmHg. Associations were analyzed using bivariate analysis and simplified exploratory multivariable logistic regression. RESULTS: Among 101 patients, hyponatremia and respiratory failure occurred in 51.5% and 20.8%, respectively. Respiratory failure was more frequent with hyponatremia than without hyponatremia (34.6% vs. 6.1%; odds ratio [OR]: 8.12, 95% confidence interval [CI]: 2.21–29.79; P < 0.001). In the exploratory multivariable model, hyponatremia (adjusted OR [aOR] 6.05, 95% CI: 1.58–23.14; P = 0.009) and tuberculosis (aOR 8.05, 95% CI: 1.73–37.37; P = 0.008) remained associated with respiratory failure. The model showed acceptable discrimination (area under the curve: 0.769, 95% CI: 0.652–0.885), with sensitivity 85.7% (95% CI: 63.7%–97.0%), specificity 56.3% (95% CI: 44.7%–67.3%), positive predictive value 34.0% (95% CI: 21.5%–48.3%), and negative predictive value 93.8% (95% CI: 82.8%–98.7%). CONCLUSION: Among lung cancer patients, hyponatremia was prevalent and associated with respiratory failure at ER admission. These findings are exploratory and hypothesis-generating.