Role of electrolyte abnormalities and unmeasured anions in the metabolic acid-base abnormalities in dogs with parvoviral enteritis

Background: The strong ion model (SIM) is an alternative paradigm in the characterization of acid-base disturbances particularly in complex disorders. Hypothesis/Objectives: To compare the acid-base changes in dogs with parvoviral enteritis (PE) using the Henderson-Hasselbalch (HH) approach, with 2 strong ion approaches. Animals: Forty-four dogs with PE, and 16 age-matched control dogs. Methods: Prospective controlled observational study. Acid-base status was evaluated using the HH model, Fencl-Stewart (FS) approach and a validated strong ion model (VDM). The acid-base changes according to each model were classified and compared. Statistical correlations between pH, CO₂, and various SIM variables were performed, as well as between the sum of effects (SOE) of the SIM and the individual variables comprising the SOE. Results: The HH model identified acid-base disorders in 31/44 cases of which 16/31 were mixed with metabolic acidosis and concurrent respiratory alkalosis the most common (10/31). Using the FS approach, metabolic changes were present 36/42 cases, with changes in free water (FW), chloride, and unmeasured anions (UA) being the most prevalent. Both FW and UA correlated well with pH; however, UA were most consistently abnormal in severe acidemia. Similarly to the HH, the VDM detected acid-base disturbances in 28/44 cases. Major contributors to the acid-base changes were hyponatremia, hypochloremia, and A_tot acidosis because of elevated globulins and increased UA. Conclusions and Clinical Importance: Acid-base changes are common and complex in dogs with PE, and were easier to understand using a SIM paradigm. Increases in UA have not been documented in PE in dogs.