Fink effect

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 agent N₂O (nitrous oxide) are breathed in large quantities they can be dissolved in body fluids rapidly. This leads to a temporary increase^{[ clarification needed ]} in both the concentrations and partial pressures of oxygen 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 N₂O anaesthesia, 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]}

See also

• Concentration effect  – Effect affecting the pulmonary alveolar gas concentration during anesthesia
• Inhalational anesthetic  – Volatile or gaseous anesthetic compound delivered by inhalation
• Second gas effect  – Effect occurring during general anesthesia

References

1. J. Roger Maltby (2002). Notable Names in Anaesthesia. Royal Society of Medicine Press. p. 63. ISBN   978-1-85315-512-3.
2. S. Ahanatha Pillai (2007). Understanding Anaesthesiology. Jaypee Brothers Publishers. p. 101. ISBN   978-81-8448-169-3.
3. Steven M. Yentis; Nicholas P. Hirsch; Gary B. Smith (2009). Anaesthesia and Intensive Care A–Z: An Encyclopedia of Principles and Practice. Elsevier Health Sciences. ISBN   978-0-443-06785-3.
4. Bernard R. Fink (1955). "Diffusion Anoxia". Anesthesiology . 16 (4): 511–519. doi: 10.1097/00000542-195507000-00007 . PMID   13238868.
5. S. EINARSSON (1993). "Nitrous Oxide Elimination and Diffusion Hypoxia During Normo- and Hypoventilation". British Journal of Anaesthesia. 71 (2): 189–93. doi: 10.1093/bja/71.2.189 . PMID   8123390.
6. Andrew B. Lumb; John F. Nunn (2005). Nunn's Applied Respiratory Physiology (6th ed.). Elsevier/Butterworth Heinemann. p. 169. ISBN   978-0-7506-8791-1.
7. "Entonox". AnaesthesiaUK (www.frca.co.uk). 26 January 2009. Archived from the original on 31 October 2007. Retrieved 27 February 2017.
8. Joanne D. Fisher; Simon N. Brown; Matthew W. Cooke (October 2006). UK Ambulance Service Clinical Practice Guidelines (2006) (PDF). Joint Royal Colleges Ambulance Liaison Committee. ISBN   1-84690-060-3. Archived (PDF) from the original on 5 June 2011. Retrieved 27 February 2018.