Intrapulmonary shunting is defined as what physiologic process?

• A. Bypassing of oxygen-poor blood past nonfunctional alveoli to the left side of the heart.
• B. Bypassing of oxygen-rich blood past nonfunctional alveoli to the left side of the heart.
• C. Normal diffusion of oxygen from alveoli to blood.
• D. Mixing of oxygenated and deoxygenated blood in the pulmonary arteries.

Answer: (B)

Intrapulmonary shunting happens when blood passes through portions of the lung that are perfused but not ventilated. That blood bypasses the gas-exchange surface and returns to the left heart without becoming oxygenated. The result is arterial blood that is less oxygenated, contributing to hypoxemia that may not fully improve with supplemental oxygen because the issue lies with perfused but nonventilated lung units, not with the diffusion of oxygen into fully ventilated alveoli. In short, it’s perfusion of nonfunctional alveoli leading to blood that bypasses oxygenation entirely.