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TheFink effect, also known as "diffusionanoxia",[1] "diffusionhypoxia",[2]or the "second gas effect",[3]is a factor that influences thepO2 (partial pressure of oxygen) within thepulmonary alveoli. When water-soluble gases such asanesthetic agent N2O (nitrous oxide) are breathed in large quantities they can bedissolved inbodyfluids rapidly. This leads to a temporary increase[clarification needed] in both theconcentrations and partialpressures ofoxygen andcarbon dioxide in the alveoli.
The effect is named afterBernard 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 theblood into the alveoli (down its concentrationgradient) and so for a short period of time, theO2 andCO2 in the alveoli are diluted by this gas. A sufficiently large decrease in the partial pressure of oxygen leads tohypoxia, 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 andhypoxia can be avoided by increasing the fractional inspired oxygen concentration when recovering from N2O administration.[6]It is for this reason thatEntonox, a 50:50 gaseous mixture ofnitrous oxide andoxygen, 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]
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