In right or biventricular chronic heart failure addition of thiazides to loop diuretics to achieve a sequential blockade of the nephron is associated with increased risk of dilutional hyponatremia: results of a case-control study.

AIM: Chronic hyponatremia is frequently found in some syndromes characterized by widespread edema coupled to impairment in arterial effective circulating volume, such as congestive chronic heart failure (CHF). In this setting, it is unclear whether the hyponatremia itself makes this condition worse or whether it represents a simply marker of decompensation. The factors responsible for development of hyponatremia in CHF have not exhaustively been elucidated yet. The aim of this paper was to ascertain whether some laboratory, clinical and therapeutical factors are able to predict occurrence of hyponatremia in CHF patients.
METHODS: A case-control study was carried out by recruiting 57 CHF patients, whose 19 characterized by hyponatremia (serum Na+<135 mEq/L) and 38 controls, matched for age, sex, etiology of CHF, time elapsed since beginning of both symptoms and diuretic therapy. Eligibility criteria included right or biventricular heart failure in NYHA class III, absence of hyponatremia at the first visit and therapy at enrollment with oral dose not less than 175 mg per week of furosemide or equivalent weekly dose of torsemide. Exclusion criteria were electrostimulation therapies (pace-maker or cardiac resynchronization therapy), documented episodes- one or more- of infective gastroenteritis or diarrhea and use of any drug influencing neuroendocrine mechanisms of arginin-vasopressin (AVP) secretion, such as opiates, tetracyclines, phenothiazines, lithium, serotonin selective reuptake inhibitors (SSRIs) etc.
RESULTS: At univariate analysis, intensive intravenous (iv) therapy with furosemide (one or more courses), ascites, mixed regimen with thiazide diuretic plus furosemide, high (>3 ng/mL/h) plasma renin activity, serum creatinine ≥2,2 mg/dl and oligoanuria were shown to be associated with hyponatremia. At multivariate analysis a role of predictor of hyponatremia was maintained by combined therapy with thiazide diuretic plus furosemide (OR=35.68 95%CI: 2.83-449.37 P=0.0057) as well as by intensive iv furosemide therapy (OR=12.44 95%CI: 1.207-128.27 P=0.0342).
CONCLUSION: Inhibition of free water clearance by thiazides may account for association found between their use and hyponatremia development in congestive CHF setting. Even though loop diuretics are known to promote free water excretion, in our experience hyponatremia might have been favored by iv furosemide high doses, because drop in effective circulating volume and further impairment in arterial underfilling due to overzealous iv loop diuretic administration are able to foster AVP non osmotic release, thereby leading to hemodilution hyponatremia.