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.
(© 2020 The Authors. Journal of Veterinary Internal Medicine published by Wiley Periodicals LLC. on behalf of the American College of Veterinary Internal Medicine.)