Acid Based Disturbances

C.M. Elwood MA VetMB CertSAC MSc PhD MRCVS DACVIM DECVIM
Davies Veterinary Specialists

Major disturbances in acid-base balance can be a life-threatening feature of many medical emergencies (e.g. hypoadrenocorticism, acute renal failure, ethylene glycol intoxication). Effective patient-side assessment and treatment of acid-base disturbances requires an ability to determine blood pH, P_CO2, [HCO₃^-] and base excess. Addition of electrolyte (Na⁺, K⁺, and Cl^-) allows calculation of anion gap and strong ion differences, which can assist in further classification and diagnosis of cause. Blood gas analysis needs to be performed quickly and easily, ideally close to the patient, thus preventing problems with sample deterioration and allowing intervention in a realistic time-scale. Modern, in-clinic, relatively cheap analysers (e.g. I-STAT) have made these ideals much more achievable.

Acidosis and alkalosis are physiologic processes tending to produce acid or alkali. Whereas the blood pH can be normal with acidosis and alkalosis, acidaemia and alkalaemia refer to changes in blood pH. Maintenance of stable pH is essential for optimal function of normal cellular function through normal cellular chemistry and enzyme function.

Understanding regulation of the body’s acid-base status can be difficult, especially when faced with lots of complex chemistry and mathematical equations. A practical, clinically useful, understanding, however, can be gained through concentration on a few key areas, and through regular practice in interpretation of data, preferably in a clinical setting.