Anaesthesia Fundamentals | Physiology | Co2 Carriage in Blood and Acid-Base Equilibrium

CO2 Carriage in Blood and Acid-Base Equilibrium
Session overview
Description
This session covers the physiology of how carbon dioxide is carried by blood, including its conversion into bicarbonate ions and the role of the red blood cell and haemoglobin in this process. The session also describes how buffers work, and the fundamentals of acid-base balance under both physiological and pathological circumstances.

Learning objectives
By the end of this session you will be able to:

• Describe the principles of a buffer system
• Describe the different systems by which carbon dioxide is transported by blood
• Explain the role of the red blood cell and haemoglobin in carbon dioxide transport
• Derive the Henderson-Hasselbalch equation and understand the relationship between its components
• Describe the principle causes, diagnosis of, and effects of common acid-base abnormalities

In biological systems, carbon dioxide is a major determinant of pH, and extensive buffering systems exist to minimise the effects of changes in CO2 partial pressure.

Transporting carbon dioxide from its site of production in the tissues to the lung is therefore vital to maintain optimal pH for cellular function. Most carbon dioxide is carried in the blood as bicarbonate, the formation of which is facilitated in red blood cells by carbonic anhydrase (CA) and the ability of haemoglobin to buffer the hydrogen ions formed. Smaller amounts of CO2 are carried in simple solution in blood or by binding to proteins.

The relationship between partial pressure of CO2, bicarbonate concentration and pH is described by the Henderson-Hasselbalch equation, which may be used to understand the various abnormalities of these three quantities that can occur.