UF Veterinary Student University of Florida Gainesville, Florida, United States
Abstract:
Background: Heart failure-associated hypochoremia can be depletional or dilutional from free water retention. Serum osmolality reflects free water, but has not been evaluated in dogs with heart disease. Hypothesis/
Objectives: To determine if serum osmolality is related to heart disease stage and the amount of mathematical correction of serum chloride (Cl-) concentrations in healthy dogs and dogs with myxomatous mitral valve degeneration (MMVD). Animals: Seventy-seven dogs (20 healthy, 25 Stage B MMVD, 32 Stage C/D MMVD).
Methods: Serum Cl- was mathematically corrected. Osmolality was calculated (cOsm) and directly measured by freezing point depression (dmOsm) and compared by Bland-Altman analysis. Biochemical variables and osmolarity were compared among healthy, Stage B and Stage C/D dogs. Correlations were explored between osmolality and biochemical variables. Median and IQR are presented and P < .05 was considered significant.
Results: The cOsm was different among groups (P=.003), with Stage B (310 mOsm/kg; 306, 316) and C/D dogs (312 mOsm/kg; 308, 319) having higher cOsm than healthy dogs (305 mOsm/kg; 302, 308). Osmolality methods were moderately correlated (P < .0001, r=0.46) but with proportional bias and poor agreement. The amount of Cl- correction was negatively correlated with cOsm (P < .0001, r=-0.78) and dmOsm (P=.004, r=-.33). Serum bicarbonate was negatively correlated with Cl- (P < .0001, r=-.67). Conclusions and clinical importance: Dogs with Stage B and Stage C/D heart disease had higher cOsm than healthy dogs. Osmolality was inversely related to the amount of Cl- correction which supports its use in the assessment of relative free water. Poor agreement between cOsm and dmOsm prevents methodological interchange.
