Contemporary approach to acid-base balance and its disorders in dogs and cats

The issue of the acid-base balance (ABB) parameters and their disorders in pets is rarely raised and analysed, though it affects almost 30% of veterinary clinics patients. Traditionally, ABB is described by the Henderson-Hasselbach equation, where blood pH is the resultant of HCO3- and pCO2 concentrations. Changes in blood pH caused by an original increase or decrease in pCO2 are called respiratory acidosis or alkalosis, respectively. Metabolic acidosis or alkalosis are characterized by an original increase or decrease in HCO3- concentration in the blood. When comparing concentration of main cations with this of main anions in the blood serum, the apparent absence of anions, i.e., anion gap (AG), is observed. The AG value is used in the diagnostics of metabolic acidosis. In 1980s Stewart noted, that the analysis of: pCO2, difference between concentrations of strong cations and anions in serum (SID) and total concentration of nonvolatile weak acids (Atot), provides a reliable insight into the body ABB. The Stewart model analyses relationships between pH change and movement of ions across membranes. Six basic types of ABB disorders are distinguished. Respiratory acidosis and alkalosis, strong ion acidosis, strong ion alkalosis, nonvolatile buffer ion acidosis and nonvolatile buffer ion alkalosis. The Stewart model provides the concept of strong ions gap (SIG), which is an apparent difference between concentrations of all strong cations and all strong anions. Its diagnostic value is greater than AG, because it includes concentration of albumin and phosphate. The therapy of ABB disorders consists, first of all, of diagnosis and treatment of the main disease. However, it is sometimes necessary to administer sodium bicarbonate (NaHCO3) or tromethamine (THAM).