The amount of O₂ delivered to tissues is equal to the amount contained in the blood (the arterial O₂ content) times the cardiac output (CO): CO = stroke volume × the heart rate (Figure 21-1). The arterial O₂ content is a product of the hemoglobin (Hb) concentration in grams per deciliter times the amount of O₂ in each gram of Hb times the O₂ saturation, expressed as a fraction, usually given as 1.39 mL of O₂ for every gram of Hb. The affinity of Hb for O₂ (Figure 21-1) determines the characteristics of the oxyhemoglobin (HbO₂) dissociation curve, with pH, temperature, and concentration of 2,3-diphosphoglycerate (2,3-DPG) having the greatest impact on the affinity of Hb for O₂. Five variables affect O₂ delivery: (1) Hb concentration, (2) Hb affinity for O₂ (P₅₀), (3) percent O₂ saturation of Hb (SaO₂), (4) CO, and (5) the amount of O₂ dissolved in blood (usually trivial amounts).

The arterial O₂ content (CaO₂) is calculated as the sum of the O₂ bound by Hb and the O₂ dissolved in the plasma.

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