Pin Index Safety System

{{short description|Component of medical gas supply systems}} {{Redirect|PISS|other uses|Piss (disambiguation)}} thumb|340x340px|Pin index dimensions

The '''Pin Index Safety System''' ('''PISS''') is a means of connecting high pressure cylinders containing medical gases to a regulator or other utilization equipment. It uses geometric features on the valve and yoke to prevent mistaken use of the wrong gas. This system is widely used worldwide for anesthesia machines, portable oxygen administration sets, and inflation gases used in surgery.

==Concept==

The pin index safety system uses a face seal between the cylinder valve and the associated yoke clamp. There are two holes in specific positions on the cylinder valve body below the outlet port, in positions associated with the gas mixture, which prevent connection of the cylinder to a yoke or pressure regulator with a mis-matched set of pins. The holes accept pins 4&nbsp;mm diameter by 6&nbsp;mm long which are correctly aligned with the holes.<ref name="Srivastava" />

==Pin index configurations== frame|Pin numbers Each gas cylinder has a pin configuration to fit its respective gas yoke. Refer to the diagram for pin numbers; dimensions are in millimeters. * O₂: 2,5<ref name="pin code" /><ref name="pin code 2" /><ref name="Srivastava" /> * N₂O: 3,5<ref name="pin code" /><ref name="pin code 2" /><ref name="Srivastava" /> * Mixture of O₂ and N₂O (50% / 50%), commonly called Entonox: 7 (a single pin, located in the centre) * Air: 1,5<ref name="pin code 2" /><ref name="Srivastava" /> * Mixtures of CO₂ and O₂ with more than 7% CO₂: 1,6<ref name="pin code" /> * Mixtures of CO₂ and O₂ with less than 7% CO₂: 2,6<ref name="pin code" /> * He: No pin<ref name="Srivastava" /> * Mixtures of O₂ and He with less than 80% He, commonly called Heliox: 2,4<ref name="pin code" /> * Mixtures of O₂ and He with more than 80% He: 4-6<ref name="pin code" /> * Cyclopropane: 3,6<ref name="pin code" /> * Ethylene: 1,3<ref name="pin code" /> * Nitrogen: 1,4<ref name="Srivastava" />

<gallery> File:Pin index yoke connector for medical oxygen filling whip P8160068.jpg|Pin index yoke connector for medical oxygen filling whip File:Pin index yoke connector for medical oxygen filling whip P8160069.jpg|Detail of pin index yoke connector for medical oxygen File:Pin index medical oxygen cylinder valve P8160080.jpg|Pin index medical oxygen cylinder valve </gallery>

==International Standards== * International (ISO) and European (CEN) Standard :*EN ISO 407 : Small medical gas cylinders - Pin-index yoke-type valve connections

The pin index system is a safety system (PISS) designed to ensure the correct gas is filled into the correct cylinder, and that the cylinder will only connect to the correct equipment. The positions of the holes on the cylinder valve correspond with the pins fitted to the yoke attached to the equipment. The pin positions for each medical gas are unique. If an attempt is made to fit the wrong gas cylinder to the yoke a tight seal will not be made, as the pins cannot locate.{{cn|date=February 2022}}

The system requires a seal between the yoke and valve to prevent leakage. This is called a ''Bodok seal'', and is a moulded rubber washer (or Neoprene) supported by a metal rim.<ref name="Srivastava" />

==Bodok seal== thumb|Bodok Seal The '''Bodok seal''' is a specialised washer that ensures a gas-tight seal between the cylinder yoke or regulator of an anaesthetic machine or any medical device requiring a gas supply, and a gas cylinder. It was introduced along with the pin index safety system during the 1950s.

Attachment and detachment of a gas cylinder leads to constant wear and tear, due in part to mechanical distress and to gaseous compression and expansion. Adiabatic effects in rapidly expanding compressed gases can generate very low temperatures, necessitating a sufficiently durable and cold-resistant material such as neoprene. Prior to the introduction of the Bodok seal, the traditional fibre washer would frequently splay and cause leakage or adhere to the regulator, thus requiring the use of pliers and considerable force to remove it.

The Bodok seal consists of a neoprene washer with a peripheral metal reinforcing ring to prevent splaying. The seal is incombustible and resistant to the high pressures imposed upon it by cylinder gases, approximately {{convert|2000|psi|bar|abbr=on}} in a full cylinder.

Care must be taken when replacing gas cylinders that the Bodok seal does not stick to the cylinder valve face, and is thus 'lost' when the new cylinder is fitted, preventing a gas tight seal.

Bodok seals are also used in emergency oxygen kits used in first aid for underwater diving, but diving regulators used for scuba cylinders generally use a conventional o-ring seal with either a DIN 477 or CGA 850 yoke connector.

== Limitations == It is possible to bypass the pin-index system if the pins are removed, damaged or corroded, if extra washers are used, or on some valves with a short face above the orifice, by inverting the gas cylinder. There is one report of the cylinder being painted the wrong colour leading to error.<ref name="Naithani et al">{{Cite journal|last2=Betkekar|first2=Sneha Arun |last1=Naithani|first1=Udita|last3=Verma|first3=Devendra |last4=Gehlot |first4=Ravindra K |last5=Sundararaj |first5=Rajkumar |date=1 October 2016|title=Pin index safety system and color coding: is it enough?|journal=Ain-Shams Journal of Anaesthesiology|language=en|volume=9|issue=4|pages=626|doi=10.4103/1687-7934.198257|s2cid=136526015 |doi-access=free }}</ref><ref name="Healy and Knight 2003">{{Cite book|url=https://books.google.com/books?id=Uh-0XJkj-C8C&q=pin+index+system+attached+upside+down&pg=PA471|title=Wylie Churchill-Davidson's A Practice of Anesthesia 7th Edition|last1=Healy|first1=Thomas EJ|last2=Knight|first2=Paul R.|date=31 October 2003|publisher=CRC Press|isbn=9780340731307|language=en|accessdate=13 August 2017}}</ref><ref name="Goho and Kittle 1991">{{Cite journal|last1=Goho|first1=C.|last2=Kittle|first2=P.|date=July 1991|title=Override of an N2O/O2 machine fail-safe mechanism: case report|url=http://www.aapd.org/assets/1/25/Goho-13-04.pdf|journal=Pediatric Dentistry|volume=13|issue=4|pages=234–235|issn=0164-1263|pmid=1886828}}</ref><ref name="Rawstron and McNeill 1962">{{Cite journal|last1=Rawstron|first1=R. E.|last2=McNeill|first2=T. D.|date=1 August 1962|url=https://academic.oup.com/bja/article/34/8/591/264992/PIN-INDEX-SYSTEM|journal=British Journal of Anaesthesia|volume=34 |issue=8|pages=591–592|doi=10.1093/bja/34.8.591|issn=0007-0912|accessdate=13 August 2017|title=Pin Index System|doi-access=free}}</ref>

==Alternative systems==

Medical gas cylinders larger than size E (679 liters) are more likely to be fitted with threaded connectors. The connections used for larger cylinders vary widely among jurisdictions. One such system are the American CGA fittings.<ref name="CGA" /> In Europe there are British Standard (BS), German Standard (DIN) and French (AFNOR) connections, and Japan has the Japanese Standard (JIS).

== Blanking plugs ==

Blanking plugs (dummy cylinder heads) can be inserted into empty yokes to ensure that there is no leak out of the yoke when not in use.<ref>{{Cite book|title=Ward's anaesthetic equipment.|last1=Davey|first1=Andrew|last2=Diba|first2=Ali|date=2012|publisher=Elsevier|others=Davey, Andrew J., Diba, Ali., Ward, C. S. (Crispian Stanley).|isbn=9780702030949|edition=6th|location=Edinburgh|pages=69|chapter=4|oclc=802047752}}</ref>

== See also == * Diameter Index Safety System, used for lower pressure connections of medical gases

==References== <references>

<ref name="CGA">{{cite web|url=https://www.concoa.com/cgachart.html|title=CGA Fitting Reference |website=www.concoa.com|last=staff|accessdate=12 August 2017}}</ref>

<ref name="pin code">{{cite web |url=http://www.crcresources.com/files/medical_gas_safety.pdf |title=Attaching Therapy Equipment: Pin Index Safety System |work=Medical Gases and Safety Systems: CRC 330 |publisher=Cardiorespiratory Care, University of South Alabama |accessdate=12 August 2017 |archive-date=28 October 2015 |archive-url=https://web.archive.org/web/20151028104643/http://crcresources.com/files/medical_gas_safety.pdf |url-status=dead }}</ref>

<ref name="pin code 2">{{cite web|url=https://healthprofessions.udmercy.edu/academics/na/agm/03.htm|title=Supply system: Gases & electricity|work=The Anesthesia Gas Machine|first1=Michael P. |last1=Dosch |first2= Darin |last2=Tharp|publisher=University of Detroit|accessdate=12 August 2017}}</ref>

<ref name="Srivastava">{{cite journal|journal=Indian Journal of Anaesthesia|title=Anaesthesia gas supply: Gas cylinders|first=Uma |last=Srivastava|year= 2013 |volume=57 |issue =5 |pages = 500–506|doi=10.4103/0019-5049.120147|pmid=24249883|pmc=3821267 |doi-access=free }}</ref>

</references>

==External links== * [https://web.archive.org/web/20090920151249/http://medind.nic.in/iad/t04/i3/iadt04i3p228.pdf Bodok seal note] (See "Historical Forum" following "Nerve Plexus" article)

Category:Safety equipment Category:Anesthetic equipment