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 Atot 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.