Felis ISSN 2398-2950

Acid base imbalance

Introduction

• The regulation of acid-base balance is a very important component of homeostasis.
• Normal metabolic processes produce vast quantities of carbon dioxide (CO₂) (volatile acid) and hydrogen ions (H^₊) (fixed acid) every day.
• CO₂ is combined with water to form carbonic acid (H₂CO₃) which dissociates to generate H⁺ and HCO₃^-. This is described by the carbonic anhydrase equation which is crucial to the understanding of acid-base physiology:
  • H⁺ + HCO₃^-  ⇌ H₂CO₃ ⇌ CO₂ + H₂0
• What is measured in acid-base analysis is pH. pH can be described by the following 2 equations:
  • pH = -log10[H⁺]
  • pH = 6.1 + log([HCO₃^-]/0.03 x PCO₂)
• As you can see, pH is determined by the H⁺ in the carbonic anhydrase equation. 
• And, pH can also be determined by HCO₃ (which is excreted and absorbed by the gastrointestinal tract and kidneys); and CO₂ (which is regulated by the respiratory tract).
• Acid-base regulation also involves integrated normal activity of the lungs, kidney and liver. The lungs excrete CO₂, the kidneys excrete H⁺ as part of the ammonium ion (NH4⁺), and the liver produces H⁺ from metabolism of protein.
• The body uses 3 principle ways of buffering changes in [H⁺], thereby keeping pH as near normal as possible:
  • Chemical buffers such as bicarbonate, phosphate and proteins act within seconds to resist changes in pH.
  • Although the respiratory tract compensates for metabolic acid base abnormalities in most species, cats are unable to do this.
  • The kidney excretes excess H⁺ in the urine and also synthesizes new HCO₃^- over a period of hours or days.

Clinical aspects of acid-base balance

Interpreting blood gas analysis

Primary acid-base disturbances