Oxygen Content of Blood

Overview

• ~15.0 g/dL hemoglobin in blood
  • most oxygen in blood is attached to hemoglobin
  • > 5.0 g/dL deoxyhemoglobin in blood → cyanosis
  • ↓ hemoglobin → ↓ O₂ content
  • ↓ hemoglobin does not change O₂ saturation, arterial PO₂
    • chronic lung disease → ↓ arterial PO₂
      • physiologic shunt → ↓ O₂ extraction ratio
• 1.0 g hemoglobin can bind 1.34 mL O₂
• O₂ binding capacity 
  • = (15.0 g hemoglobin / dL blood) x (1.34 mL O₂ / 1.0 g hemoglobin) = 20.1 mL O₂ / dL
• O₂ content = (O₂ binding capacity) x (% saturation) + dissolved O₂ 
  • dissolved oxygen can usually be ignored because it is multiplied by 0.003 to correct for units (mL O₂ / mmHg / dL), and becomes negligible
• O₂ delivery = (cardiac output) x (O₂ content)