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 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.