Correction of serum chloride concentration in dogs with congestive heart failure

Abstract 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.