Correction of serum chloride concentration in dogs with congestive heart failure

BACKGROUND: Hypochloremia associated with congestive heart failure (CHF) in dogs is likely multifactorial. Loop diuretics cause 1:2 sodium [Na(+)]:chloride [Cl(−)] loss, whereas water retention causes a 1:1 [Na(+)]:[Cl(−)] dilution. Mathematical [Cl(−)] correction separates these effects on [Cl(−)]. HYPOTHESIS: We hypothesized that corrected [Cl(−)] (c[Cl(−)]) would not differ from measured [Cl(−)] (m[Cl(−)]) in dogs with controlled CHF because of loop diuretics, and dogs with refractory CHF would have higher c[Cl(−)] than m[Cl(−)], indicating relative water excess. ANIMALS: Seventy‐one client‐owned dogs with acquired heart disease, without CHF (NO‐CHF), 76 with Stage C CHF and 24 with Stage D CHF. METHODS: Clinicopathological data from a previous study were retrospectively analyzed. Corrected [Cl(−)], m[Cl(−)], and differences were compared among NO‐CHF, Stage C CHF, and Stage D CHF, using the formula: c[Cl(−)] = (mid‐reference range [Na(+)]/measured [Na(+)]) × m[Cl(−)]. RESULTS: Corrected [Cl(−)] and m[Cl(−)] were lower in Stage D vs Stage C and NO‐CHF (all P < .0001). The c[Cl(−)] was higher than m[Cl(−)] in Stage D (P < .0001) but not Stage C or NO‐CHF. Median difference between c[Cl(−)] and m[Cl(−)] was higher for Stage D vs Stage C (P = .0003). No hypochloremic Stage D dogs had normal c[Cl(−)], but 11/24 had [Cl(−)] that was increased by >2 mmol/L. CONCLUSIONS AND CLINICAL IMPORTANCE: Serum [Cl(−)] increased after mathematical correction in Stage D CHF dogs but not in Stage C and NO‐CHF dogs. Although c[Cl(−)] was higher than m[Cl(−)] in Stage D dogs supportive of relative water excess, hypochloremia persisted, consistent with concurrent loop diuretic effects on electrolytes. Future study correlating c[Cl(−)] to antidiuretic hormone concentrations is warranted.