Relationship between Serum Sodium Levels and Length of Hospital Stay in Patients with Pulmonary Hypertension associated with Left Heart Disease

Background Pulmonary hypertension (PH) associated with left heart disease (PH-LHD) is the most common form of PH. Studies have shown that serum sodium is associated with the severity and poor prognosis of group 1 PH, but the effect of serum sodium on PH-LHD has rarely been reported. Objective To investigate the relationship between serum sodium and N-terminal pro-brain natriuretic peptide (NT-proBNP) and echocardiographic indexes in PH-LHD patients, and evaluate the effect of serum sodium on the severity and length of stay of PH-LHD, so as to provide theoretical basis for clinical diagnosis and treatment of PH-LHD patients and improvement of hospital turnover. Methods The clinical data of 360 adult inpatients diagnosed with PH-LHD in the First Hospital of Shanxi Medical University from January 2020 to February 2022 were collected. According to the median serum sodium of 139 mmol/L (serum sodium <135 mmol/L is hyposodium), the patients were divided into 3 groups: <135 mmol/L group (n=50), 135-139 mmol/L group (n=136) and 140-145 mmol/L group (n=174). Spearman correlation analysis was used to explore the correlation of serum sodium level with length of hospital stay, NT-proBNP and echocardiographic indicators. Kaplan-Meier was used to compare the length of hospital stay of PH-LHD patients with different serum sodium levels. Binary Logistic regression analysis was used to investigate the effect of serum sodium levels on the length of hospital stay in PH-LHD patients. Results Age, length of stay, NT-proBNP, left atrial diameter, right atrium area, left ventricular ejection fraction and shortening fraction of PH-LHD patients in 3 groups were compared, and the differences were statistically significant (P<0.05). The length of hospitalization and NT-proBNP of patients in the serum sodium 140-145 mmol/L group were lower than those in the serum sodium <135 mmol/L group and the serum sodium 135-139 mmol/L group (P<0.05). Spearman correlation analysis showed that serum sodium level was negatively correlated with length of stay (rs=-0.176), NT-proBNP (rs=-0.135), right ventricular diameter (rs=-0.110) and pulmonary artery systolic pressure (rs=-0.105) in PH-LHD patients (P<0.05). The Kaplan-Meier survival showed that there were statistically significant differences between the length of hospital stay among the three groups of PH-LHD patients with different serum sodium levels. Binary Logistic regression analysis showed that increased serum sodium level was a protective factor for longer hospital stay in PH-LHD patients after correcting each control variable (OR=0.916, 95%CI=0.859-0.977, P=0.008). The risk of prolonged hospitalization was elevated in patients with serum sodium <135 mmol/L and those with serum sodium 135-139 mmol/L compared with patients with serum sodium 140-145 mmol/L. Conclusion Serum sodium level is closely related to the severity of PH-LHD, and decreased serum sodium level is an independent risk factor for the length of hospital stay in PH-LHD patients. It is a potential therapeutic consideration, providing new strategies for the diagnosis and treatment of PH-LHD and hospital turnover.