Canis ISSN: 2398-2942

Acid base imbalance

Contributor(s): John Dodam, Elisa Mazzaferro, 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 + H2O
  • What is measured in acid-base analysis is pH. pH can be described by the folliwing 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.
    • Respiratory system → responds within minutes to resist changes in [H+] by altering the partial pressure of carbon dioxide and eliminating excess CO2 (volatile acid), thereby excreting excess H+ ions.
    • 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

This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login

Interpreting blood gas analysis

This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login

Primary acid-base disturbances

This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login

Further Reading

Publications

Refereed papers

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

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.


ADDED