Hyponatremia Clinical Update, August 2, 2011

The latest clinical research into the causes and treatment of hyponatremia.

The presence of hyponatraemia in outpatients with heart failure (HF) is associated with increased risk of hospitalization or death, according to the results of a recent study.

The aim of the study, which was conducted to researchers in the department of cardiology at Rigshospitalet in Copenhagen, Denmark, was to determine the prevalence and prognostic significance of hyponatraemia in a large cohort of HF outpatients followed in clinics participating in the Danish Heart Failure Clinics Network.

The study, which was published in the European Journal of Heart Failure, consisted of a population of consecutive patients referred for HF management in 18 Danish heart failure clinics. “Overall, 2,863 patients (83%) had a normal plasma sodium (p-sodium) level and 602 patients (17%) had hyponatraemia with a p-sodium level <136 mmol/L. Outcome data were obtained from a validated, national registry. Patients were elderly with a mean age of 68 years,” the researchers wrote in the study's abstract.

The mean P-[Na+] was 139.6 ± 2.4 mmol/L among patients with normonatraemia and 132.4 ± 3.2 mmol/L among patients with hyponatraemia. In multivariate Cox Proportional Hazard Models adjusted for confounders (age, gender, hospitalization within the last 90 days, loop diuretics, creatinine level, systolic blood pressure, New York Heart Association class III-IV, left ventricular ejection fraction <0.46, ischaemic heart disease and diabetes) hyponatraemic patients had increased risk of hospitalization or death [hazard ratio (HR) 1.2 (95% confidence interval (CI) 1.0-1.4, P = 0.011)].

“Hyponatraemia was also an independent predictor of all-cause mortality [HR 1.5 (95% CI 1.2-1.9, P< 0.001)]. There was no interaction between hyponatraemia and the covariables on outcome in the multivariable models,” the researchers concluded.

Higher Prevalence of Exercise-Associated Hyponatremia in Female Ultra-Endurance Swimmers

The prevalence of exercise-associated hyponatremia (EAH) was greater in female than in male open-water ultra-endurance swimmers, recent research has concluded.

Researchers at the Institute of General Practice and Health Services Research at the University of Zurich in Switzerland investigated the prevalence of EAH in 25 male and 11 female open-water ultra-endurance swimmers participating in the Marathon-Swim in Lake Zurich, which covers a distance of 26.4 km.

Changes in body mass, fat mass, skeletal muscle mass, total body water, urine specific gravity, plasma sodium concentration [Na(+)] and haematocrit were determined.

“Two males (8%) and four females (36%) developed EAH where one female was symptomatic with plasma sodium [Na(+)] of 127 mmol/L. Body mass and plasma [Na(+)] decreased (P< 0.05). The changes in body mass correlated in both male and female swimmers to post-race plasma [Na(+)] (r = -0.67, p = 0.0002 and r = -0.80, p = 0.0034, respectively) and changes in plasma [Na(+)] (r = -0.68, p = 0.0002 and r = -0.79, p = 0.0039, respectively),” the researchers wrote in the European Journal of Applied Physiology.

Fluid intake was neither associated with changes in body mass, post-race plasma [Na(+)] or the change in plasma [Na(+)]. Sodium intake showed no association with either the changes in plasma [Na(+)] or post-race plasma [Na(+)].

Sources

Prevalence and prognostic significance of hyponatraemia in outpatients with chronic heart failure [European Journal of Heart Failure]

Higher prevalence of exercise-associated hyponatremia in female than in male open-water ultra-endurance swimmers: the 'Marathon-Swim' in Lake Zurich [European Journal of Applied Physiology]