Talk:Fink effect
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Unclear explanations: decrease pO2 (stop) >< increase pO2 (start)
[edit]@CV9933: The text is not so easy to understand. The nitrous oxide (N2O) used as anaesthesic agent is more soluble in water and in the blood than O2 and CO2.
One has to consider two steps:
- Start of anesthesia: First N2O inhalation and beginning of the administration of N2O: it quickly dissolves in the blood because of its higher solubility and also because of the concentration gradient from the alveolus gas to the blood. As N2O occupies most of the volume normally taken by nitrogen (N2) in the air in the inhaled anaesthesic gas and quickly dissolves in the blood, the concentration of O2 in the alveolus increases.
- Stop of anesthesia: End of N2O inhalation and progressive desaturation / expulsion of N2O out of the body: because of the concentration gradient from the blood to the air, N2O is driven out of the body. Its concentration increases in the alveolus and consequently, the pO2 and the pCO2 decrease in the alveolus.
This could be more clearly explained in the article page by better differentiating the two phases: N2O entering the blood and N2O leaving the blood.
The Fink effect could also be clearly mentioned as a supplementary cause of health risk for the persons practicing the "recreational use" of N2O.
Is this mechanism correctly understood here above? In advance thank you for confirming, or refuting, this explanation. Shinkolobwe (talk) 13:30, 26 February 2021 (UTC)
- Hi Shinkolobwe Fink (PMID: 13238868) describes a plausible mechanism for diffusion anoxia whereby after cessation of nitrous oxide anaesthesia, the dissolved blood gas diffuses rapidly back into the alveolar space diluting the available air. He also considers several clinical situations where this effect may be significant and most likely his work helped promote routine oxygen administration post anaesthesia to aid recovery. Our job is to find the best secondary sources and summarise them to reflect what they are saying, although they might be a bit sparse here. I have a feeling that your explanation above may be departing from that obligation (synth, OR) unless you can provide the sources required. Perhaps a better way to do this would be to merge content from this article with the Second gas effect article? Regards CV9933 (talk) 11:52, 28 February 2021 (UTC)
- Hi CV9933. Thank you for your answer and your explanations. This confirms what I understood for the end of the anesthesia with the lowering of pO2 when nitrous oxide dissolved in the blood goes back to the alveoli because of the existing concentration gradient. However, what happens in the beginning of anesthesia with the increase of pO2 in the alveoli was less clear for me. It depends on the oxygen partial pressure in the inhalated gas. Obviously one cannot administrate pure N2O to a patient without running the risk of hypoxia. So, if the gas mixture only contains N2O and O2, it is quite logical to expect an increase of pO2 in the alveoli when N2O quickly dissolves into the blood. From there, my request and the explanations on what I understood on the basis of a personal physico-chemical reasoning. So, the criteria of synthesis or original research (syn, OR) might apply, while I think it is a rather simple reasoning that can be easily done by everyone with the required background. I just wanted to be certain it was correct before to write it. I just contacted you because you recently reverted an edit from someone who changed pO2 increase into decrease at the beginning of anesthesia. So, you had a reason to do it. Thank you also for your suggestion the Second gas effect article. Regards, Shinkolobwe (talk) 18:41, 28 February 2021 (UTC)