Serum sodium levels and blood pressure monitoring in heart failure: Added diagnostic and prognostic value

Hyponatremia is the electrolyte abnormality most often encountered in patients admitted for heart failure (HF). 1---3 Its prevalence ranges between 18 and 30%, 4---8 although it is lower in stable HF outpatients (10-17%). 9---12It also varies with the severity and duration of HF, the criteria used to define it, medication prescribed and drug doses, particularly of diuretics.Most studies define hyponatremia as Na <135 mEq/l, although some use quartiles, and a linear relation has been observed between risk of shortand long-term total mortality and in-hospital cardiovascular morbidity and mortality and sodium <140 mEq/l.Other studies have demonstrated a U-curve for values between 140 and 145 mEq/l. 4---12 The value of natremia as a risk indicator is thus evident even for values considered normal; for every 3 mEq/l fall in blood sodium the risk of in-hospital mortality rises by 19.5% in HF with systolic dysfunction and by 8.6% in HF with preserved systolic function, and mortality 60-90 days after discharge rises by 10-18%. 4,5Pathophysiologically, hyponatremia is multifactorial, usually due to hypervolemia related to hyperactivity of the sympathetic and rein-angiontensin-aldosterone systems and their effects on the kidneys.This hyperactivity is in turn secondary to reduced cardiac output and consequent reduced stimulation of aortic and carotid baroreceptors, which also induces an excessive increase in non-osmotic secretion of vasopressin