View source for Anaesthetic machine

{{Short description|Medical device to supply a mix of life-support and anaesthetic gases}}
{{cs1 config|name-list-style=vanc}}
{{Medref|date=February 2022}}
{{Infobox industrial process
| name           = Anaesthetic machine
| image          = Maquet Flow-I anesthesia machine.jpg
| caption        = An anaesthetic machine. This particular machine is a "Flow-I" model, manufactured by [[Maquet]], a division of [[Getinge Group]], [[Getinge]], Sweden.
| type           = [[physical change]]
| sector         = [[anaesthesiology]] ([[medicine]])
| technologies   = [[vaporization]]
| feedstock      = [[inhalational anaesthetic]] agents, chiefly [[nitrous oxide]] and [[Inhalational anaesthetic#Volatile anaesthetics|volatile anaesthetics]]
| product        = [[phase transition]] of feedstock from the [[liquid]] phase to the [[gas]] phase
| facility       = hospitals and outpatient surgery centres
| developer      =
}}

An '''anaesthetic machine''' ([[British English]]) or '''anesthesia machine''' ([[American English]]) is a [[medical device]] used to generate and mix a fresh gas flow of medical gases and [[inhalational anaesthetic]] agents for the purpose of inducing and maintaining [[anaesthesia]].

The machine is commonly used together with a [[mechanical ventilator]], [[breathing circuit|breathing system]], [[suction (medicine)|suction equipment]], and [[Medical monitor|patient monitoring]] devices; strictly speaking, the term "anaesthetic machine" refers only to the component which generates the gas flow, but modern machines usually integrate all these devices into one combined freestanding unit, which is colloquially referred to as the "anaesthetic machine" for the sake of simplicity. In the developed world, the most frequent type in use is the '''continuous-flow anaesthetic machine''' or "'''Boyle's machine'''", which is designed to provide an accurate supply of medical gases mixed with an accurate concentration of anaesthetic vapour, and to deliver this continuously to the patient at a safe [[pressure]] and flow. This is distinct from '''intermittent-flow anaesthetic machines''', which provide gas flow only on demand when triggered by the patient's own inspiration.

Simpler anaesthetic apparatus may be used in special circumstances, such as the [[triservice anaesthetic apparatus]], a simplified anaesthesia delivery system invented for the British [[Defence Medical Services]], which is light and portable and may be used for ventilation even when no medical gases are available. This device has unidirectional valves which suck in ambient air, which can be enriched with oxygen from a cylinder, with the help of a set of bellows.

==History==

The original concept of continuous-flow machines was popularised by Boyle's anaesthetic machine, invented by the British anaesthetist [[Henry Edmund Gaskin Boyle|Henry Boyle]] at [[St Bartholomew's Hospital]] in [[London]], [[United Kingdom]] in 1917, although similar machines had been in use in France and the United States.<ref name="YentisHirsch2013">{{cite book|author1=Steven M. Yentis|author2=Nicholas P. Hirsch|author3=James K. Ip|title=Anaesthesia and Intensive Care A-Z: An Encyclopaedia of Principles and Practice|chapter=Anaesthetic machine|url=https://books.google.com/books?id=M_W-55fYDyAC|date=2013|publisher=Elsevier Health Sciences|isbn=978-0-7020-4420-5|pages=34}}</ref> Prior to this time, anaesthesiologists often carried all their equipment with them, but the development of heavy, bulky cylinder storage and increasingly elaborate airway equipment meant that this was no longer practical for most circumstances. Contemporary anaesthetic machines are sometimes still referred to [[metonym]]ously as "Boyle's machine", and are usually mounted on anti-static wheels for convenient transportation.
[[File:Cyprane Trilene inhaler.png|thumb|left|Handheld anaesthetic device for [[trichloroethylene]], made in the UK, 1947. This device was designed for self-administration by the patient.]] 
Many of the early innovations in anaesthetic equipment in the United States, including the closed circuit carbon-dioxide absorber (a.k.a. the Guedel-Foregger Midget) and diffusion of such equipment to anaesthesiologists within the United States can be attributed to [[Richard von Foregger]] and [[The Foregger Company]].

==Flow rate==
In anaesthesia, fresh gas flow is the mixture of medical gases and [[volatile anaesthetic]] agents which is produced by an anaesthetic machine and has not been recirculated. The flow rate and composition of the fresh gas flow is determined by the [[anaesthetist]]. Typically the fresh gas flow emerges from the common gas outlet, a specific outlet on the anaesthetic machine to which the breathing attachment is connected.<ref name="Zhong et al 2020" />

Open circuit forms of equipment, such as the Magill attachment, require high fresh gas flows (e.g. 7 litres/min) to prevent the patient from [[rebreathing]] their own expired carbon dioxide. Recirculating (rebreather) systems, use [[soda lime]] to absorb [[carbon dioxide]], in the scrubber, so that expired gas becomes suitable to re-use. With a very efficient recirculation system, the fresh gas flow may be reduced to the patient's minimum [[oxygen]] requirements (e.g. 250ml/min), plus a little volatile as needed to maintain the concentration of anaesthetic agent.

Increasing fresh gas flow to a recirculating breathing system can reduce carbon dioxide absorbent consumption. There is a cost/benefit trade-off between gas flow and use of adsorbent material when no inhalational anaesthetic agent is used which may have economic and environmental consequences.<ref name="Zhong et al 2020" >{{cite journal |journal=British Journal of Anaesthesia |volume=125 |issue=5 |pages=773–778 |date=November 2020 |title=Environmental and economic impact of using increased fresh gas flow to reduce carbon dioxide absorbent consumption in the absence of inhalational anaesthetics |first1=George |last1=Zhong |first2=Ali |last2=Abbas |first3=Joseph |last3=Jones |first4=Sarah |last4=Kong |first5=Tim |last5=McCulloch |doi=10.1016/j.bja.2020.07.043 |doi-access=free |pmid=32859360 }}</ref>

*High flow anesthesia supplies fresh gas flow which approximates the patient’s minute ventilation, which is usually about 3 to 6 litres per minute in a normal adult.
*Low flow anesthesia supplies fresh gas flow of less than half the patient's minute ventilation of the patient, which is usually less than 3.0 litres per minute in a normal adult.
*Minimal flow anesthesia supplies fresh gas flow of about 0.5 litres per minute.
*Closed system anesthesia supplies fresh gas flow as needed to make up the recirculated gas volume to compensate for the patient’s need for oxygen and anesthetic agents.<ref name="Low flow" >{{cite web |url=https://clinicalview.gehealthcare.com/white-paper/what-and-why-low-flow-anesthesia |title=What and Why of Low Flow Anesthesia |website=clinicalview.gehealthcare.com |date=July 2020 |access-date=12 October 2023 }}</ref>

==Anaesthetic vapouriser==
[[File:Vaporizer.jpg|thumb|Anesthetic machine, showing [[sevoflurane]] (yellow) and [[isoflurane]] (purple) vaporizers on the right]]
An '''anesthetic vaporizer''' ([[American English]]) or '''anaesthetic vaporiser''' ([[British English]]) is a device generally attached to an anesthetic machine which delivers a given concentration of a [[volatile anesthetic]] agent. It works by controlling the vaporization of anesthetic agents from liquid, and then accurately controlling the concentration in which these are added to the fresh gas flow. The design of these devices takes account of varying: ambient temperature, fresh gas flow, and agent [[vapor pressure]]. There are generally two types of vaporizers: plenum and drawover. Both have distinct advantages and disadvantages.<ref name="pmid24249879">{{cite journal | vauthors = Chakravarti S, Basu S | title = Modern anaesthesia vapourisers | journal = Indian J Anaesth | volume = 57 | issue = 5 | pages = 464–71 | date = September 2013 | pmid = 24249879 | pmc = 3821263 | doi = 10.4103/0019-5049.120142 | doi-access = free }}</ref> The ''dual-circuit gas-vapor blender'' is a third type of vaporizer used exclusively for the agent [[desflurane]].

===Plenum vaporizers===
The plenum vaporizer is driven by [[positive pressure]] from the [[anesthetic machine]], and is usually mounted on the machine. The performance of the vaporizer does not change regardless of whether the patient is breathing spontaneously or is mechanically ventilated. The internal resistance of the vaporizer is usually high, but because the supply pressure is constant the vaporizer can be accurately [[calibrated]] to deliver a precise concentration of [[volatile anesthetic]] vapor over a wide range of fresh gas flows.<ref name="pmid24249879"/> The plenum vaporizer is an elegant device which works reliably, without external power, for many hundreds of hours of continuous use, and requires very little maintenance.

The plenum vaporizer works by accurately splitting the incoming gas into two streams. One of these streams passes straight through the vaporizer in the bypass channel. The other is diverted into the vaporizing chamber. Gas in the vaporizing chamber becomes fully [[Saturated vapor|saturated]] with volatile anesthetic vapor. This gas is then mixed with the gas in the bypass channel before leaving the vaporizer.

A typical volatile agent, [[isoflurane]], has a saturated [[vapor pressure]] of 32kPa (about 1/3 of an atmosphere). This means that the gas mixture leaving the vaporizing chamber has a [[partial pressure]] of isoflurane of 32kPa. At sea-level ([[atmospheric pressure]] is about 101kPa), this equates conveniently to a [[concentration]] of 32%. However, the output of the vaporizer is typically set at 1–2%, which means that only a very small proportion of the fresh gas needs to be diverted through the vaporizing chamber (this proportion is known as the splitting ratio). It can also be seen that a plenum vaporizer can only work one way round: if it is connected in reverse, much larger volumes of gas enter the vaporizing chamber, and therefore potentially toxic or lethal concentrations of vapor may be delivered. (Technically, although the dial of the vaporizer is calibrated in volume percent (e.g. 2%), what it actually delivers is a partial pressure of anesthetic agent (e.g. 2kPa)).

The performance of the plenum vaporizer depends extensively on the saturated vapor pressure of the volatile agent. This is unique to each agent, so it follows that each agent must only be used in its own specific vaporizer. Several safety systems, such as the Fraser-Sweatman system, have been devised so that filling a plenum vaporizer with the wrong agent is extremely difficult. A mixture of two agents in a vaporizer could result in unpredictable performance from the vaporizer.

Saturated vapor pressure for any one agent varies with temperature, and plenum vaporizers are designed to operate within a specific temperature range. They have several features designed to compensate for temperature changes (especially cooling by [[evaporation]]). They often have a metal jacket weighing about 5&nbsp;kg, which equilibrates with the temperature in the room and provides a source of heat. In addition, the entrance to the vaporizing chamber is controlled by a [[bimetallic strip]], which admits more gas to the chamber as it cools, to compensate for the loss of efficiency of evaporation.

The first temperature-compensated plenum vaporizer was the Cyprane 'FluoTEC' [[Halothane]] vaporizer, released onto the market shortly after Halothane was introduced into clinical practice in 1956.

===Drawover vaporizers===
The drawover vaporizer is driven by [[Pressure#Negative pressures|negative pressure]] developed by the patient, and must therefore have a low resistance to gas flow. Its performance depends on the [[minute volume]] of the patient: its output drops with increasing minute ventilation.

The design of the drawover vaporizer is much simpler: in general it is a simple glass reservoir mounted in the breathing attachment. Drawover vaporizers may be used with any liquid volatile agent (including older agents such as [[diethyl ether]] or [[chloroform]], although it would be dangerous to use [[desflurane]]). Because the performance of the vaporizer is so variable, accurate calibration is impossible. However, many designs have a lever which adjusts the amount of fresh gas which enters the vaporizing chamber.

The drawover vaporizer may be mounted either way round, and may be used in circuits where [[rebreathing|re-breathing]] takes place, or inside the circle breathing attachment.

Drawover vaporizers typically have no temperature compensating features. With prolonged use, the liquid agent may cool to the point where condensation and even frost may form on the outside of the reservoir. This cooling impairs the efficiency of the vaporizer. One way of minimising this effect is to place the vaporizer in a bowl of water.

The relative inefficiency of the drawover vaporizer contributes to its safety. A more efficient design would produce too much anesthetic vapor. The output concentration from a drawover vaporizer may greatly exceed that produced by a plenum vaporizer, especially at low flows. For safest use, the concentration of anesthetic vapor in the breathing attachment should be continuously monitored.

Despite its drawbacks, the drawover vaporizer is cheap to manufacture and easy to use. In addition, its portable design means that it can be used in the field or in [[veterinary anesthesia]].

===Dual-circuit gas–vapor blender===
The third category of vaporizer (the dual-circuit gas–vapor blender) was created specifically for the agent [[desflurane]].<ref name="pmid24249879"/> Desflurane boils at 23.5&nbsp;°C, which is very close to room temperature. This means that at normal [[operating temperature]]s, the saturated vapor pressure of desflurane changes greatly with only small fluctuations in temperature. This means that the features of a normal plenum vaporizer are not sufficient to ensure an accurate concentration of desflurane. Additionally, on a very warm day, all the desflurane would boil, and very high (potentially lethal) concentrations of desflurane might reach the patient.

A desflurane vaporizer (e.g. the TEC 6 produced by [[Datex-Ohmeda]]) is heated to 39C and pressurized to 194kPa.<ref name="Boumphrey_Marshall_2011">{{cite journal | vauthors = Boumphrey S, Marshall N| title = Understanding vaporizers | journal = Continuing Education in Anaesthesia Critical Care & Pain | publisher=Elsevier BV | volume=11 | issue=6 | year=2011 | issn=1743-1816 | doi=10.1093/bjaceaccp/mkr040 | pages=199–203| doi-access=free }}</ref> It is mounted on the anesthetic machine in the same way as a plenum vaporizer, but its function is quite different. It evaporates a chamber containing desflurane using heat, and injects small amounts of pure desflurane vapor into the fresh gas flow. A [[transducer]] senses the fresh gas flow.<ref name="pmid24249879"/>

A warm-up period is required after switching on. The desflurane vaporizer will fail if mains power is lost. Alarms sound if the vaporizer is nearly empty. An electronic display indicates the level of desflurane in the vaporizer.

The expense and complexity of the desflurane vaporizer have contributed to the relative lack of popularity of desflurane, although in recent years it is gaining in popularity.

=== Historical vaporizers ===
Historically, [[diethyl ether|ether]] (the first volatile agent) was first used by [[John Snow (physician)|John Snow]]'s inhaler (1847) but was superseded by the use of [[chloroform]] (1848). Ether then slowly made a revival (1862–1872) with regular use via [[Curt Schimmelbusch]]'s "mask", a [[Unconsciousness|narcosis]] mask for dripping liquid ether. Now obsolete, it was a mask constructed of wire, and covered with cloth.

Pressure and demand from [[dental surgeon]]s for a more reliable method of administering ether helped modernize its delivery. In 1877, [[Joseph Thomas Clover|Clover]] invented an ether inhaler with a water jacket, and by the late 1899 alternatives to ether came to the fore, mainly due to the introduction of spinal anesthesia. Subsequently, this resulted in the decline of ether (1930–1956) use due to the introduction of [[cyclopropane]], [[trichloroethylene]], and [[halothane]]. By the 1980s, the anesthetic vaporizer had evolved considerably; subsequent modifications lead to a raft of additional safety features such as temperature compensation, a [[bimetallic strip]], temperature-adjusted splitting ratio and anti-spill measures.

==Components of a typical machine==
[[Image:anesthesia machine simple schm.png|thumb|Simple schematic of an anaesthetic machine]]
[[File:Adjustable pressure-limiting valve anaesthetic machine.jpg|thumb|right|The adjustable pressure-limiting valve on a General Electric Datex-Ohmeda Aisys anaesthetic machine, with pressure gradations shown in centimetres of water]]

The ''breathing circuit'' is the ducting through which the breathing gases flow from the machine to the patient and back, and includes components for mixing, adjusting, and monitoring the composition of the breathing gas, and for removing carbon dioxide.

A modern anaesthetic machine includes at minimum the following components:<ref name="YentisHirsch2013"/>
* Connections to piped [[oxygen]], [[medical air]], and [[nitrous oxide]] from a wall supply in the healthcare facility, or reserve [[gas cylinder]]s of oxygen, air, and nitrous oxide attached via a [[pin index safety system]] yoke with a [[Bodok seal]]
* Pressure gauges, regulators and 'pop-off' valves, to monitor gas pressure throughout the system and protect the machine components and patient from excessive rises. An adjustable pressure-limiting valve (commonly abbreviated to APL valve, and also referred to as an expiratory valve, relief valve or spill valve) is part of the [[Breathing circuit]] which allows excess gas to leave the system while preventing ambient air from entering.<ref name="Al-ShaikhStacey2013">{{cite book |author1=Baha Al-Shaikh |author2=Simon Stacey |title=Essentials of Anaesthetic Equipment |url=https://books.google.com/books?id=9jNV55CcAXcC |date=2013 |publisher=Elsevier Health Sciences |isbn=978-0-7020-4954-5 |pages=55–73 |chapter=Breathing systems }}</ref>
* [[Flowmeters]] such as [[rotameter]]s for oxygen, air, and nitrous oxide
* [[Anaesthetic vaporiser|Vaporiser]]s to provide accurate dosage control when using volatile anaesthetics
* A high-flow oxygen flush, which bypasses the flowmeters and vaporisers to provide pure oxygen at 30-75 litres/minute
* Systems for monitoring the gases being administered to, and exhaled by, the patient, including an [[oxygen failure warning device]]
Systems for monitoring the patient's [[heart rate]], [[Electrocardiography|ECG]], [[Sphygmomanometer|blood pressure]] and [[Oxygen saturation (medicine)|oxygen saturation]] may be incorporated, in some cases with additional options for monitoring [[Capnography|end-tidal carbon dioxide]] and [[temperature]].<ref name="YentisHirsch2013"/> [[Ventilator|Breathing systems]] are also typically incorporated, including a manual [[reservoir bag]] for ventilation in combination with an [[adjustable pressure-limiting valve]], as well as an integrated mechanical ventilator, to accurately ventilate the patient during anaesthesia.<ref name="YentisHirsch2013"/>

Anaesthetic machines are distinct from [[anesthesia cart|anaesthesia carts]], which hold various adjuncts for anaesthesia such as intravenous medications, syringes, needles and other items of equipment that the anesthetist providing anaesthesia might need.{{cn|date=January 2024}}

In [[dentistry]] a simplified version of the anaesthetic machine, without a ventilator or anaesthetic vaporiser, is referred to as a [[relative analgesia machine]]. By using this machine, the dentist can administer a mild inhalation [[sedation]] with nitrous oxide and oxygen, in order to keep their patient in a conscious state while depressing the feeling of pain.{{cn|date=January 2024}}

==Safety features of modern machines==
Based on experience gained from analysis of mishaps, the modern anaesthetic machine incorporates several safety devices, including:
* an oxygen failure alarm (a.k.a. 'Oxygen Failure Warning Device' or OFWD). In older machines this was a pneumatic device called a Ritchie whistle which sounds when oxygen pressure is 38 psi descending. Newer machines have an electronic sensor.
* Nitrous cut-off or oxygen failure protection device, OFPD: the flow of medical nitrous-oxide is dependent on oxygen pressure. This is done at the regulator level. In essence, the nitrous-oxide regulator is a 'slave' of the oxygen regulator. i.e., if oxygen pressure is lost then the other gases can not flow past their regulator.
* [[Hypoxia (medical)|hypoxic]]-mixture alarms (hypoxy guards or ratio controllers) to prevent gas mixtures which contain less than 21–25% oxygen being delivered to the patient. In modern machines it is impossible to deliver 100% nitrous oxide (or any hypoxic mixture) to the patient to breathe. Oxygen is automatically added to the fresh gas flow even if the anaesthesiologist should attempt to deliver 100% nitrous oxide. Ratio controllers usually operate on the pneumatic principle or are chain linked (link 25 system). Both are located on the rotameter assembly, unless electronically controlled.
* ventilator alarms, which warn of low or high airway pressures.
* interlocks between the vaporizers preventing inadvertent administration of more than one volatile agent concurrently
* alarms on all the above physiological monitors
* the [[Pin Index Safety System]] prevents cylinders being accidentally connected to the wrong yoke
* the NIST (Non-Interchangeable Screw Thread) or Diameter Index Safety System, DISS system for pipeline gases, which prevents piped gases from the wall being accidentally connected to the wrong inlet on the machine
* pipeline gas hoses have non-interchangeable [[Schrader valve]] connectors, which prevents hoses being accidentally plugged into the wrong wall socket

The functions of the machine should be checked at the beginning of every operating list in a "cockpit-drill". Machines and associated equipment must be maintained and serviced regularly.

Older machines may lack some of the safety features and refinements present on newer machines. However, they were designed to be operated without [[mains electricity]], using compressed gas power for the ventilator and suction apparatus. Modern machines often have [[battery (electricity)|battery]] backup, but may fail when this becomes depleted.

The modern anaesthetic machine still retains all the key working principles of the Boyle's machine (a [[The BOC Group|British Oxygen Company]] trade name) in honour of the British anaesthetist Henry Boyle. In India, however, the trade name 'Boyle' is registered with Boyle HealthCare Pvt. Ltd., Indore MP.

A two-person pre-use check (consisting of an anaesthesiologist and an assistant) of the anaesthetic machine is recommended before each case and has been shown to decrease the risk of 24-hour severe postoperative morbidity and mortality.<ref name=Arbous>{{cite journal|author=Arbous|journal=Anesthesiology|year=2005|volume=102|doi=10.1097/00000542-200502000-00005|pmid=15681938|issue=2|title=Impact of anesthesia management characteristics on severe morbidity and mortality|pages=257–68; quiz 491–2|display-authors=etal|hdl=1874/12590|hdl-access=free}}</ref> Various regulatory and professional bodies have formulated checklists for different countries.<ref name=vam>{{cite web|url=http://vam.anest.ufl.edu/guidelines.html|title = International Anesthesia Equipment Checkout Recommendations - Virtual Anesthesia Machine}}</ref> Machines should be cleaned between cases as they are at considerable risk of contamination with [[pathogen]]s.<ref name=Baillie2007>{{cite journal|doi=10.1111/j.1365-2044.2007.05261.x|volume=62|issue=12|pages=1257–61|last=Baillie|first=JK|author2=P. Sultan |author3=E. Graveling |author4=C. Forrest |author5=C. Lafong |title=Contamination of anaesthetic machines with pathogenic organisms|journal=Anaesthesia|year=2007|pmid=17991263|s2cid=24338540|doi-access=free}}</ref>

==See also==
* {{annotated link|Anaesthesia}}
* {{annotated link|Anaesthetic vaporiser}}
* {{annotated link|Breathing apparatus}}
* {{annotated link|Carbon dioxide scrubber}}
* {{annotated link|Ether Dome}}
* {{annotated link|History of general anesthesia}}
* {{annotated link|Soda lime}}
* {{annotated link|Ventilator}}

== References ==
{{reflist | 30em}}

==Further reading==
* {{cite journal|last=Boumphrey|first=S.|author2=Marshall, N.|title=Understanding vaporizers|journal=Continuing Education in Anaesthesia, Critical Care & Pain|date=10 November 2011|volume=11|issue=6|pages=199–203|doi=10.1093/bjaceaccp/mkr040|doi-access=free}}
* {{cite journal|last=Eales|first=Mike|author2=Cooper, Robin|title=Principles of anaesthetic vaporizers|journal=Anaesthesia & Intensive Care Medicine|date=March 2007|volume=8|issue=3|pages=111–115|doi=10.1016/j.mpaic.2006.12.013}}
* {{cite journal|last=Hahn|first=CE|author2=Palayiwa, E|author3= Sugg, BR|author4= Lindsay-Scott, D|title=A microprocessor-controlled anaesthetic vaporizer.|journal=British Journal of Anaesthesia|date=Oct 1986|volume=58|issue=10|pages=1161–6|pmid=3768229|doi=10.1093/bja/58.10.1161|doi-access=free}}
* {{cite journal|last=Zuck|first=D|title=The development of the anaesthetic vaporizer.|journal=Anaesthesia|date=September 1988|volume=43|issue=9|pages=773–775|doi=10.1111/j.1365-2044.1988.tb05754.x|pmid=3052161|s2cid=31549505|doi-access=free}}
* {{cite journal|last=Sjølie|first=K|title=[Danger in tipping of anesthetic vaporizers].|journal=Tidsskrift for den Norske Laegeforening|date=Mar 30, 1989|volume=109|issue=9|pages=966–7|pmid=2705180|language=Norwegian}}
* {{cite book|author1=Andrew J Davey|author2=Ali Diba|title=Ward's Anaesthetic Equipment|url=https://books.google.com/books?id=5Cix7y3CYDsC&pg=PA48|date=25 April 2012|publisher=Elsevier Health Sciences|isbn=978-0-7020-4878-4|pages=48}}
* {{cite book|author1=Patrick Magee|author2=Mark Tooley|title=The Physics, Clinical Measurement and Equipment of Anaesthetic Practice|url=https://books.google.com/books?id=OYlXsS2eDoIC&pg=PA51|date=January 2005|publisher=Oxford University Press|isbn=978-0-19-850859-5|pages=51}}
* {{cite book|author1=Baha Al-Shaikh|author2=Simon Stacey|title=Essentials of Anaesthetic Equipment4: Essentials of Anaesthetic Equipment|url=https://books.google.com/books?id=9jNV55CcAXcC&pg=PA30|year=2013|publisher=Elsevier Health Sciences|isbn=978-0-7020-4954-5|pages=30}}

== External links ==
{{Commonscat|Anaesthetic machines}}
* [http://vam.anest.ufl.edu/wip.html Virtual Anesthesia Machine (VAM)] — a free transparent reality simulation of a generic anaesthetic machine from the [[University of Florida]]
* [https://web.archive.org/web/20100417095724/http://www.simanest.org/ Various anaesthesia-related simulations]
* [http://www.virtual-anesthesia-textbook.com Virtual Anaesthesia Textbook]
* [https://web.archive.org/web/20101123082222/http://www.anaesthesiauk.com/ AnaesthesiaUK.com] — resources for UK anaesthetists in training
* [https://web.archive.org/web/20110724133106/http://www.lifelongcompany.com/ History of Richard von Foregger and the Foregger Company] — written by his son, R. Foregger, this website chronicles one of the leading manufacturers and developers of anesthesiology equipment in the early 20th century.
* [http://medinstrum.com/anesthesia-equipments Anesthesia Equipment & Instruments:] Definitions & Principles of Practical Usage
* [https://www.howequipmentworks.com/vaporisers/ Free resource which graphically explains the principles of anesthesia vaporizers] on howequipmentworks.com
* [https://web.archive.org/web/20160304044004/http://www.vet.mut.ac.th/main_object/vetkm/anesthetic_machine_for_mtu.pdf Anesthetic machine]: a presentation
* [https://web.archive.org/web/20140423044556/http://www.udmercy.edu/crna/agm/05.htm The Anesthesia Gas Machine] by Michael P. Dosch
* [https://web.archive.org/web/20130124045039/http://frca.co.uk/article.aspx?articleid=100151 Precision vaporisers] on Anaesthesia.UK
* [http://www.vetequip.com/pdfs/Vaporizer%20Manual.pdf Operating Instructions & Maintenance Guidelines for Precision Vaporizers]

{{Anesthesia}}
{{Breathing apparatus|medical}}
{{Dosage forms|state=}}

{{DEFAULTSORT:Anaesthetic Machine}}
[[Category:Anesthetic equipment]]
[[Category:Machines]]
[[Category:Drug delivery devices]]
[[Category:Dosage forms]]
[[Category:Breathing apparatus]]