A 50-year-old man at rest has a hemoglobin of 15 g/dL, PaO2 of 98 mmHg, and SaO2 of 98%. His cardiac output is 5 L/min. Calculate his oxygen delivery (DO2) in mL/min. (O2 binding capacity of hemoglobin = 1.34 mL O2/g Hb; ignore dissolved O2)

• A DO2 = (15 × 1.34 × 0.98) × 5 × 10 = 985 mL/min ✓
• B DO2 = (15 × 1.34 × 0.98) × 5 = 98.5 mL/min
• C DO2 = 15 × 1.34 × 5 = 100.5 mL/min
• D DO2 = (15 × 1.34 × 0.98 + 0.003 × 98) × 5 × 10 = 999 mL/min

Explanation

Oxygen delivery: DO2 = CaO2 × CO, where CaO2 (arterial oxygen content) = (Hb × 1.34 × SaO2) + (0.003 × PaO2). Ignoring dissolved O2: CaO2 = 15 × 1.34 × 0.98 = 19.7 mL/dL. CO = 5 L/min = 50 dL/min. DO2 = 19.7 × 50 = 985 mL/min. The key is to express CO in dL/min (multiply by 10) or convert CaO2 from mL/dL to mL/L: 19.7 × 10 = 197 mL/L, then × 5 L/min = 985 mL/min. Option B forgets the ×10 conversion factor (uses CO in L/min without converting dL). Option C omits SaO2. Option D includes dissolved O2 correction (approximately +1.4 mL/min) giving ~999 mL/min, which while more complete, the question specifies to ignore dissolved O2.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.