Changes

*Increases indicate an alkalaemia.

*Increases indicate an alkalaemia.

*Decreases indicate an acidemia.

*Decreases indicate an acidemia.

It is essential that 50-100meq of acid is excreted by the kidneys every day.  This is achieved by secretion of H⁺ in two regions of the nephron, the proximal tubule and the collecting ducts, and is essential for maintaining the acid base ratio, within the body, at the correct levels. If there is a net gain or loss of H⁺ within the body then the kidneys will compensate for it.  The H⁺ ions cannot be secreted as free ions, however virtually all filtered HCO₃^- must be reabsorbed.  The result is that the H⁺ ions bind to other filtered buffers which are not fully reabsorbed such as ammonia or phosphate.  Extracellular pH is the main physiological regulator affecting how much acid is secreted.  In pathological states circulating volume, aldosterone and plasma potassium affect it.

In healthy animals, it is essential that 50-100meq of acid is excreted by the kidneys every day.  This is achieved by secretion of H⁺ in two regions of the nephron, the proximal tubule and the collecting ducts, and is essential for maintaining the acid base ratio, within the body, at the correct levels. If there is a net gain or loss of H⁺ within the body then the kidneys will compensate for it.  The H⁺ ions cannot be secreted as free ions, however virtually all filtered HCO₃^- must be reabsorbed.  The result is that the H⁺ ions bind to other filtered buffers which are not fully reabsorbed such as ammonia or phosphate.  Extracellular pH is the main physiological regulator affecting how much acid is secreted.  In pathological states circulating volume, aldosterone and plasma potassium affect it.

[[Image:buffereg1ap.jpg|right|thumb|200px|<small><center>The HPO₄^-Buffer System</center></small>]]

[[Image:buffereg1ap.jpg|right|thumb|200px|<small><center>The HPO₄^-Buffer System</center></small>]]

The kidneys work with the respiratory system to regulate H⁺.  Where as the respiratory systems quickly compensates for a problem it is left to the kidneys to actually remove the problem and restore a proper balance.  They do this by altering the plasma concentration of HCO₃^-.  During anaesthesia, the body's short term mechanism of respiratory change to regulate acid/base balance is compromised by the effects of the anaesthetic, and must be monitored so that relevant changes can be made manually by the anaesthetist to restore the correct acid base balance.  

The kidneys work with the respiratory system to regulate H⁺.  Where as the respiratory systems quickly compensates for a problem it is left to the kidneys to actually remove the problem and restore a proper balance.  They do this by altering the plasma concentration of HCO₃^-.  During anaesthesia, the body's short term mechanism of respiratory change to regulate acid/base balance is compromised by the effects of the anaesthetic, and must be monitored so that relevant changes can be made manually by the anaesthetist to restore the correct acid base balance.