carbon content

carbon content

Critical care
A measure of the relative blood concentration of CO2, measured by pH electrodes, by enzymes or based on changes in pH. CO2 content is rarely measured outside of hospital settings.

Ref range
< age 2: 18–28 mmol/L.
> 2 years: venous 22–26 mmol/L.
> 2 years: arterial 22–32 mmol/L.

Decreased in
Respiratory alkalosis, hyperventilation, metabolic acidosis.
 
Increased in
Severe vomiting, gastric drainage, hypoventilation—e.g., emphysema or pneumonia.
 
Physiology
The blood picks up O2 and, as it passes through the lungs, releases CO2, which, with water, are the endproducts of O2 metabolism; some of the CO2 in the blood is changed to bicarbonate (HCO3) and is excreted in the kidneys. Measurement of CO2 is part of “blood gas measurement”, which is used to evaluate the ease with which gases are exchanged through the lungs and determine the factors affecting the acid-base balance, or pH, of the blood.

Specimen
Venous or arterial blood, collected in a specially sealed syringe to avoid contact with air.

Method
Spectrophotometry.
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