1599 1600 ## 2. Carbon Dioxide 1601 1602 1603 1604 Carbon dioxide is transported in blood in three forms: dissolved in solution, as bicarbonate, and with proteins in the form of carbamino compounds (Table 23–5). The sum of all three forms is the total CO2 content of blood (routinely reported with electrolyte measurements). 1605 1606 *TABLE 23–5 Contributions to carbon dioxide transport in 1 L of whole blood.* 1607 1608 1609

Form	Plasma	Erythrocytes	Combined	Contribution (%)
Mixed venous whole blood
Dissolved CO₂	0.76	0.51	1.27	5.5
Bicarbonate	14.41	5.92	20.33	87.2
Carbamino CO₂	Negligible	1.70	1.70	7.3
Total CO₂	15.17	8.13	23.30
Arterial whole blood
Dissolved CO₂	0.66	0.44	1.10	5.1
Bicarbonate	13.42	5.88	19.30	89.9
Carbamino CO₂	Negligible	1.10	1.10	5.1
Total CO₂	14.08	7.42	21.50

1610 1611 *Values are expressed in millimoles, except where indicated otherwise.* 1612 1613 *Data from Nunn JE. Nunn's Applied Physiology. 4th ed. Philadelphia, PA: Butterworth; 2000.* 1614 1615 1616 ## Dissolved Carbon Dioxide 1617 1618 Carbon dioxide is more soluble in blood than O2, with a solubility coefficient of 0.031 mmol/L/mm Hg (0.067 mL/dL/mm Hg) at 37°C. 1619 1620 1621 ## Bicarbonate 1622 1623 In aqueous solutions, CO2 slowly combines with water to form carbonic acid and bicarbonate, according to the following reaction: 1624 1625 H2O + CO2 ↔ H2CO3 ↔ H+ + HCO3- 1626 1627 15 1628 1629 In plasma, although less than 1% of the dissolved CO2 undergoes 1630 1631 this reaction, the presence of the enzyme carbonic anhydrase within 1632 1633 1634 1635 erythrocytes and endothelium greatly accelerates the reaction. As a result, bicarbonate represents the largest fraction of the CO2 in blood (see Table 23–5). Administration of acetazolamide, a carbonic anhydrase inhibitor, can impair CO2 transport between tissues and alveoli. 1636 1637 On the venous side of systemic capillaries, CO2 enters red blood [... Output truncated due to length. 992 tokens/3165 characters removed ...]