Article of the Week


We will be posting commentaries on articles relating to internal medicine and endocrinology that we think are of interest.


June 10th, 2021

Clinical relevance of serum electrolytes in dogs and cats with acute heart failure: A retrospective study


In both human and veterinary medicine, electrolyte abnormalities occur in congestive heart failure (CHF) cases. This is thought to be due to neurohormonal activation by the renin-angiotensin aldosterone (RAAS) and arginine vasopressin (AVS) systems, and because of the diuretic therapy initiated in such cases. For decades, the fundamental role of sodium (Na) in fluid homeostasis and heart failure (HF) progression has been well established in human medicine.  Hyponatremia has sparked extensive interest as a strong predictor of adverse events, including worsened survival, rehospitalization and prolonged length of hospitalization in people with CHF. A retrospective study performed in dogs with acute CHF demonstrated similar results, with significantly lower Na concentrations in nonsurvivors. However, recent evidence suggests that serum chloride (Cl) concentrations, either at admission or at discharge, are more closely related to survival, renal function, and loop diuretic doses than Na in people with both acute or chronic HF. The reason for this is suspected to be multifactorial, and related to Cl's unique neurohormonal and homeostatic roles. While the fluid retention caused by maladaptive neurohormonal activation and arginine vasopressin release creates a “dilutional effect” decreasing both Na and Cl in equivalent proportions, the formal perception of Cl operating only as a passive anion linked to Na concentrations is currently contested. It is now thought that Cl has a specific and critical role in regulating HF physiology in people. Human patients with low serum Cl concentrations are suspected of having an excessive RAAS activation and potentially decreased diuretic efficacy, also commonly referred to as diuretic resistance. In dogs with chronic CHF, serum Cl concentration is a strong differentiator between heart disease stages. A cut-off of <103.5 mmol/L accurately identifies stage D cases, which comprises dogs suspected of having or developing diuretic resistance.


This unveils a potential connection between hypochloremia and diuretic resistance in dogs with chronic CHF. However, data on the implications of electrolyte abnormalities on diuretic dosing, diuretic response and prognostic variables in small animals with acute presentation of CHF are lacking. Thus, the aims of this retrospective study in dogs and cats with acute CHF were 3-fold: (a) to document the electrolyte abnormalities present upon admission, (b) to assess the association between serum electrolyte concentrations and diuretic dose, and (c) to evaluate the prognostic impact of serum electrolyte concentrations, as reflected by duration of hospitalization and survival time.


Background: Hypochloremia is a strong negative prognostic factor in humans with congestive heart failure (CHF), but the implications of electrolyte abnormalities in small animals with acute CHF are unclear.


Objectives: To document electrolyte abnormalities present upon admission of small animals with acute CHF, and to assess the relationship between electrolyte concentrations and diuretic dose, duration of hospitalization and survival time.


Animals: Forty-six dogs and 34 cats with first onset of acute CHF.


Methods: Retrospective study. The associations between electrolyte concentrations and diuretic doses were evaluated with Spearman rank correlation coefficients. Relationship with duration of hospitalization and survival were assessed by simple linear regression and Cox proportional hazard regression, respectively.


Results: The most commonly encountered electrolyte anomaly was hypochloremia observed in 24% (9/46 dogs and 10/34 cats) of cases. In dogs only, a significant negative correlation was identified between serum chloride concentrations at admission (median 113 mmol/L [97-125]) and furosemide doses both at discharge (median 5.2 mg/kg/day [1.72-9.57]; r = -0.59; P < .001) and at end-stage heart failure (median 4.7 mg/kg/day [2.02-7.28]; r = -0.62; P = .005). No significant hazard ratios were found for duration of hospitalization nor survival time for any of the electrolyte concentrations.


Conclusions and Clinical Importance: The observed association between serum chloride concentrations and diuretic doses suggests that hypochloremia could serve as a marker of disease severity and therapeutic response in dogs with acute CHF.