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The Fink effect, also known as "diffusion anoxia",[1] "diffusion hypoxia",[2] or the "second gas effect",[3] is a factor that influences the pO2 (partial pressure of oxygen) within the pulmonary alveoli. When water-soluble gases such as anesthetic agentN2O (nitrous oxide) are breathed in large quantities they can be dissolvedinbody fluids rapidly. This leads to a temporary increase[clarification needed] in both the concentrations and partial pressuresofoxygen and carbon dioxide in the alveoli.
The effect is named after Bernard Raymond Fink (1914–2000), whose 1955 paper first explained it.[1][4] When a patient is recovering from N2Oanaesthesia, large quantities of this gas cross from the blood into the alveoli (down its concentration gradient) and so for a short period of time, the O2 and CO2 in the alveoli are diluted by this gas. A sufficiently large decrease in the partial pressure of oxygen leads to hypoxia, especially if the patient hypoventilates (which allows more time for evolving nitrous to dilute alveolar oxygen each breath).[5] Nonetheless, this effect only lasts a couple of minutes and hypoxia can be avoided by increasing the fractional inspired oxygen concentration when recovering from N2O administration.[6] It is for this reason that Entonox, a 50:50 gaseous mixture of nitrous oxide and oxygen, is suitable for use by para-medical staff such as ambulance officers: it provides sufficient nitrous oxide for pain relief with sufficient oxygen to avoid hypoxia.[7][8]
