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Diffusion Hypoxia Prevention

Diffusion hypoxia, also known as the Fink Effect, is essentially the reverse of the second gas effect and occurs at the end of an anesthetic when nitrous oxide is being utilized. As nitrous oxide moves rapidly from the blood into the alveoli, the oxygen content of the alveoli is diluted. This causes a decreased PAO2 leading to decreased PaO2. Some older reviews indicate this is most likely to occur with nitrous oxide concentrations above 70% and switching directly to room air. This effect can be easily prevented if FiO2 is increased at the end nitrous oxide administration.


  1. Peyton PJ, Chao I, Weinberg L, Robinson GJB, Thompson BR. Nitrous Oxide Diffusion and the Second Gas Effect on Emergence from Anesthesia. Anesthesiology. 2011; 114: 596-602. PubMed Link

Other References

  1. Banks A, Hardman JG. Nitrous Oxide. Continuing Education in Anaesthesia Critical Care, and Pain 2005; 5: 145-148. Link