Acute care: Arterial blood gases
In the third part of our series,Nicola Cooper explains the finer details of arterial blood gases
The body is continually producing acid as a byproduct of metabolism. However, it must also maintain a narrow range of pH values necessary for normal enzymic activity. This narrow range of pH values is maintained by intracellular and extracellular buffers and then by the kidneys and lungs. The most important buffer system in the body is the carbonic acid-bicarbonate system
H2O+CO2 * H2CO3 * HCO3+H+
Unlike other buffer systems, the components of the carbonic acid-bicarbonate system can be varied independently of each other. Adjusting the rate of alveolar ventilation changes carbon dioxide (CO2) concentrations, and the kidneys regulate secretion of protons (H+) in urine. The excretory functions of the lungs and kidneys are connected by H2CO3 (carbonic acid). This is the respiratory-metabolic link. If the kidneys or lungs become overwhelmed, the other can help or “compensate” (table).
Measuring the anion gap is important in any metabolic acidosis to narrow down