DƯỢC LÍ Goodman & Gilman's The Pharmacological Basis of Therapeutics 12th, 2010

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Table 19–4
SECTION II
NEUROPHARMACOLOGY
The Carriage of Oxygen in Blood a
ARTERIAL O 2
CONTENT (mL O 2
/L)
MIXED VENOUS O 2
CONTENT (mL O 2
/L)
ARTERIAL PO 2
BOUND TO MIXED VENOUS PO 2
BOUND TO
kPa (mmHg) DISSOLVED HEMOGLOBIN TOTAL kPa (mmHg) DISSOLVED HEMOGLOBIN TOTAL EXAMPLES
4.0 (30) 0.9 109 109.9 2.7 (20) 0.6 59 59.6 High altitude; respiratory
failure breathing air
12.0 (90) 2.7 192 194.7 5.5 (41) 1.2 144 145.2 Normal person
breathing air
39.9 (300) 9.0 195 204 5.9 (44) 1.3 153 154.3 Normal person
breathing 50% O 2
79.7 (600) 18 196 214 6.5 (49) 1.5 163 164.5 Normal person
breathing 100% O 2
239 (1800) 54 196 250 20.0 (150) 4.5 196 200.5 Normal person breathing
hyperbaric O 2
a
This table illustrates the carriage of oxygen in the blood under a variety of circumstances. As arterial O 2
tension increases, the amount of dissolved O 2
increases in direct proportion to the PO 2
,
but the amount of oxygen bound to hemoglobin reaches a maximum of 196 mL O 2
/liter (100% saturation of hemoglobin at 15 g/dL). Further increases in O 2
content require increases in
dissolved oxygen. At 100% inspired O 2
, dissolved O 2
still provides only a small fraction of total demand. Hyperbaric oxygen therapy is required to increase the amount of dissolved oxygen to
supply all or a large part of metabolic requirements. Note that, during hyperbaric oxygen therapy, the hemoglobin in the mixed venous blood remains fully saturated with O 2
. The figures in this
table are approximate and are based on the assumptions of 15 g/dL hemoglobin, 50 mL O 2
/liter whole-body oxygen extraction, and constant cardiac output. When severe anemia is present,
arterial PO 2
remains the same, but arterial content is lower; oxygen extraction continues, resulting in lower O 2
content and tension in mixed venous blood. Similarly, as cardiac output falls
significantly, the same oxygen extraction occurs from a smaller volume of blood and results in lower mixed venous oxygen content and tension.