During anesthesia, nitrous oxide reaches equilibrium between alveolar gas and pulmonary capillary blood within the first quarter of transit through the capillary, after which no further uptake occurs along the remaining vessel length. Nitrous oxide transfer is therefore described as:

• A Diffusion limited
• B Ventilation limited
• C Reaction limited
• D Perfusion limited ✓

Explanation

Nitrous oxide is highly soluble in blood but does not bind to any blood component, so its partial pressure equilibrates very rapidly with alveolar gas. Once equilibrium occurs early in the capillary, transfer stops regardless of how long blood remains, so uptake depends only on pulmonary blood flow, making it perfusion limited. Carbon monoxide is the classic diffusion-limited gas because it binds hemoglobin so avidly that partial pressure never equilibrates.

Reference: West's Respiratory Physiology: The Essentials, 11th ed.

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Written and medically reviewed by the StethoPrep medical team.