Fink effect

{{Short description|Changes of oxygen partial pressure in the pulmonary alveoli caused by a soluble anesthetic gas}}

{{Unclear|date=February 2021}}

The Fink effect, also known as "diffusion anoxia", "diffusion hypoxia",

{{cite book

| title = Understanding Anaesthesiology

| author = S. Ahanatha Pillai

| publisher = Jaypee Brothers Publishers

| year = 2007

| isbn = 978-81-8448-169-3

| page = 101

| url = https://books.google.com/books?id=rCvEJibQstcC&q=Fink-effect%20%20hypoxia&pg=PA101

}}

or the "second gas effect",

{{cite book

| title = Anaesthesia and Intensive Care A–Z: An Encyclopedia of Principles and Practice

| author1 = Steven M. Yentis

| author2 = Nicholas P. Hirsch

| author3 = Gary B. Smith

| publisher = Elsevier Health Sciences

| year = 2009

| isbn = 978-0-443-06785-3

| url = https://books.google.com/books?id=kxxDYTV7DqUC&q=%22third%20gas%20effect%22%20fink&pg=PT534

}}

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{{Clarify|date=February 2021}} 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.

{{cite book

| title = Notable Names in Anaesthesia

| author = J. Roger Maltby

| publisher = Royal Society of Medicine Press

| year = 2002

| isbn = 978-1-85315-512-3

| page = 63

| url = https://books.google.com/books?id=Yc4_uLDkzgAC&q=Fink-effect%20%20nitrous&pg=PA63

}}

{{cite journal

| author = Bernard R. Fink

| author-link = Bernard Raymond Fink

| title = Diffusion Anoxia

| journal = Anesthesiology

| year = 1955

| volume = 16

| issue = 4

| pages = 511–519

| doi = 10.1097/00000542-195507000-00007

| pmid = 13238868

| doi-access = free

}}

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).

{{cite journal

| author = S. EINARSSON

| title = Nitrous Oxide Elimination and Diffusion Hypoxia During Normo- and Hypoventilation

| journal = British Journal of Anaesthesia

| year = 1993

| volume = 71

| issue = 2

| pages = 189–93

| doi = 10.1093/bja/71.2.189

| pmid = 8123390

| doi-access = free

}}

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.

{{cite book

| title = Nunn's Applied Respiratory Physiology

| author1 = Andrew B. Lumb

| author2 = John F. Nunn

| edition = 6th

| publisher = Elsevier/Butterworth Heinemann

| year = 2005

| isbn = 978-0-7506-8791-1

| page = 169

| url = https://books.google.com/books?id=29hqAAAAMAAJ&q=Fink-effect++intitle:Respiratory+intitle:Physiology+inauthor:Nunn

}}

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.

{{cite web

| title = Entonox

| url = http://www.frca.co.uk/article.aspx?articleid=100364

| website = AnaesthesiaUK (www.frca.co.uk)

| access-date = 27 February 2017

| date = 26 January 2009

| url-status = live

| archive-url = https://web.archive.org/web/20071031101605/http://www.frca.co.uk/article.aspx?articleid=100364

| archive-date = 31 October 2007

}}

{{cite book

| publisher = Joint Royal Colleges Ambulance Liaison Committee

| title = UK Ambulance Service Clinical Practice Guidelines (2006)

| date = October 2006

| access-date = 27 February 2018

| url = http://www2.warwick.ac.uk/fac/med/research/hsri/emergencycare/prehospitalcare/jrcalcstakeholderwebsite/guidelines/clinical_guidelines_2006.pdf

| author1 = Joanne D. Fisher

| author2 = Simon N. Brown

| author3 = Matthew W. Cooke

| isbn = 1-84690-060-3

| url-status = live

| archive-url = https://web.archive.org/web/20110605073519/http://www2.warwick.ac.uk/fac/med/research/hsri/emergencycare/prehospitalcare/jrcalcstakeholderwebsite/guidelines/clinical_guidelines_2006.pdf

| archive-date = 5 June 2011

}}