Introduction

• Acid-base balance is crucial to optimal function of body systems. 
• pH is a way of expressing [H+] which is regulated by integrated activity of respiratory and metabolic processes.
• When acid-base balance is disturbed, the signs may be referable to the respiratory system or manifest as metabolic disorders.
• H+ and CO2 are continually produced by metabolic processes. Respiratory and metabolic processes control their balance.
• CO2 combines with water to form carbonic acid (H2CO3) which dissociates to generate H+ and HCO3-. This is the bicarbonate-carbonic acid system.
• Normal equine pH is 7.35-7.45. 
• The body has several methods of buffering changes in pH:
  • The respiratory system can increase expiration of CO2, thus decreasing [H+]. This can occur relatively rapidly.
  • Chemical buffers including HCO3-, PO4, NH3, hemoglobin and other proteins can combine with excess H+.  This also occurs rapidly.
  • The kidney can excrete excess H+. This process takes hours to days.
• The bicarbonate-carbonic acid system is the most important buffer system used to clinically evaluate acid-base status.

Clinical aspects of acid base balance

Blood gas analysis

Primary acid-base disturbances

Further Reading

Publications

Refereed papers

• Recent references from PubMed and VetMedResource.
• Corley K T T & Marr C M (1998) Pathophysiology, assessment and treatment of acid-base disturbances in the horse. Equine Vet Educ 10 (5), 255-265.
• Johnson P J (1995) Electrolyte and acid-base disturbances in the horse. Vet Clin North Am Equine Pract Clin Pathol 11, 491-514 PubMed.
• Schott H C et al (1993) Fluids, electrolytes and bicarbonate. Vet Clin North Am Equine Pract 9 (3), 577-604 PubMed.

Other sources of information

• DiBartola S (2011) Fluid, Electrolyte and Acid-Base Disorders in Small Animal Ppractice. In: Small Animal Practice. 4th edn. Elsevier-Saunders, USA.
• Adams J G (2002) Metabolic Acidosis; Respiratory Acidosis; Metabolic Alkalosis; Respiratory Alkalosis. In: The 5-Minute Veterinary Consult. Eds: Brown C J & Bertone J J. Lippinocott, Williams & Wilkins, Baltimore. pp 26-33, 78-81.
• Carlson G P (1997) Fluid, Electrolyte, and Acid-Base Balance. In: Clinical Biochemistry of Domestic Animals.5th edn. Eds: Kaneko J J, Harvey J W & Bruss M L. Academic Press, USA. pp 485-516.