Felis ISSN 2398-2950

Acid base imbalance

Contributor(s): John Dodam, Duana Mcbride

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

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Interpreting blood gas analysis

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Primary acid-base disturbances

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Further Reading

Publications

Referred papers

  • Recent references from VetMed Resource and PubMed.
  • Hopper K & Haskins S (2008) A case-based review of a simplified quantitative approach to acid-base analysis. JVECC 18(5), 467-476.

Other sources of information

  • Silverstein D C & Hopper K (2015) Small Animal Critical Care Medicine. 2nd edn. Elsevier.
  • Di Bartola S P (2011) Fluid, Electrolyte, and Acid-Base Disorders. 4th edn. Elsevier.
  • Rose B D & Post T (2001) Clinical Physiology of Acid-Base and Electrolyte Disorders. 5th edn. McGraw-Hill.


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