Fluctuation of Serum Sodium and Its Impact on Short and Long-Term Mortality following Acute Pulmonary Embolism

Background
Baseline hyponatremia predicts acute mortality following pulmonary embolism (PE). The natural history of serum sodium levels after PE and the relevance to acute and long-term mortality after the PE is unknown.
Methods
Clinical details of all patients (n = 1023) admitted to a tertiary institution from 2000–2007 with acute PE were retrieved retrospectively. Serum sodium results from days 1, 3–4, 5–6, and 7 of admission were pre-specified and recorded. We excluded 250 patients without day-1 sodium or had <1 subsequent sodium assessment, leaving 773 patients as the studied cohort. There were 605 patients with normonatremia (sodium≥135 mmol/L throughout admission), 57 with corrected hyponatremia (day-1 sodium<135 mmol/L, then normalized), 54 with acquired hyponatremia and 57 with persistent hyponatremia. Patients’ outcomes were tracked from a state-wide death registry and analyses performed using multivariate-regression modelling.
Results
Mean (±standard deviation) day-1 sodium was 138.2±4.3 mmol/L. Total mortality (mean follow-up 3.6±2.5 years) was 38.8% (in-hospital mortality 3.2%). There was no survival difference between studied (n = 773) and excluded (n = 250) patients. Day-1 sodium (adjusted hazard ratio [aHR] 0.89, 95% confidence interval [CI] 0.83–0.95, p = 0.001) predicted in-hospital death. Relative to normonatremia, corrected hyponatremia increased the risk of in-hospital death 3.6-fold (95% CI 1.20–10.9, p = 0.02) and persistent hyponatremia increased the risk 5.6-fold (95% CI 2.08–15.0, p = 0.001). Patients with either persisting or acquired hyponatremia had worse long-term survival than those who had corrected hyponatremia or had been normonatremic throughout (aHR 1.47, 95% CI 1.06–2.03, p = 0.02).
Conclusion
Sodium fluctuations after acute PE predict acute and long-term outcome. Factors mediating the correction of hyponatremia following acute PE warrant further investigation.