The anatomic dead space in a 70-kg male is approximately how many milliliters?

The anatomic dead space in a 70-kg male is approximately how many milliliters?

• A. 50 mL
• B. 150 mL
• C. 250 mL
• D. 500 mL

Answer: (B)

Anatomic dead space is the air in the conducting airways that does not participate in gas exchange. In healthy adults it’s about 2 mL per kilogram of body weight, reflecting the size of the tracheobronchial tree. For a 70-kg man, that estimate gives roughly 140 mL, which is commonly rounded to about 150 mL. This value is used to determine alveolar ventilation, since the portion of each breath that reaches the alveoli equals the tidal volume minus the dead space. So, 150 mL fits the standard adult estimate (2 mL/kg, 70 kg ≈ 140 mL, rounded). The other numbers are less consistent with this rule of thumb: 50 mL is too small, 250 mL is higher than typical, and 500 mL would be closer to a tidal volume rather than dead space.

Anatomic dead space is the air in the conducting airways that does not participate in gas exchange. In healthy adults it’s about 2 mL per kilogram of body weight, reflecting the size of the tracheobronchial tree. For a 70-kg man, that estimate gives roughly 140 mL, which is commonly rounded to about 150 mL. This value is used to determine alveolar ventilation, since the portion of each breath that reaches the alveoli equals the tidal volume minus the dead space.

So, 150 mL fits the standard adult estimate (2 mL/kg, 70 kg ≈ 140 mL, rounded). The other numbers are less consistent with this rule of thumb: 50 mL is too small, 250 mL is higher than typical, and 500 mL would be closer to a tidal volume rather than dead space.