Total carbon dioxide consists of carbon dioxide (CO2) in solution or bound to proteins, bicarbonate (HCO3 ¢ ), carbonate (CO32 ¢ ), and carbonic acid (H2CO3). In practice, 80 " 90% is present as HCO3 ¢ and is a general guide to the bodys buffering capacity. It is usually measured with electrolytes as a panel.
Normal range:
0 " 2 years: 20 " 25 mmol/L
2 " 16 years: 22 " 28 mmol/L
>16 years: 24 " 32 mmol/L
Use
To evaluate the total CO32 ¢ buffering system in the body as well as the acid " base balance
Interpretation
Increased In
Respiratory acidosis with CO2 retention
Metabolic alkalosis (e.g., prolonged vomiting)
Airway obstruction
Alcoholism
Aldosteronism
Cardiac disorders
Emphysema
Fat embolism
Pulmonary dysfunction
Renal disorders
Decreased In
Respiratory alkalosis, as in hyperventilation
Metabolic acidosis (e.g., diabetes with ketoacidosis)
Alcoholic ketosis
Dehydration
Diarrhea
Head trauma
High fever
Hepatic disorders
Hyperventilation
Malabsorption syndromes
Starvation and uremia
Limitations
Antacids, corticotrophin, mercurial and thiazide diuretics, and sodium bicarbonate increase blood levels.