Editing Anesthesia (section)

=== General anesthesia ===
{{Further|General anaesthesia|General anesthetic|Inhalational anesthetic}}
[[File:Vaporizer Sevoflurane 001 JPN.jpg|thumb|A [[Vaporizer (inhalation device)|vaporizer]] holds a liquid anesthetic and converts it to gas for inhalation (in this case [[sevoflurane]]).]]
[[File:Mask Ventilation.jpg|thumb|left|A patient receiving anesthesia through inhalation]]
Anesthesia is a combination of the endpoints (discussed above) that are reached by drugs acting on different but overlapping sites in the [[central nervous system]].  General anesthesia (as opposed to sedation or regional anesthesia) has three main goals: lack of movement ([[paralysis]]), [[unconsciousness]], and blunting of the [[Fight-or-flight response|stress response]]. In the early days of anesthesia, anesthetics could reliably achieve the first two, allowing surgeons to perform necessary procedures, but many patients died because the extremes of blood pressure and pulse caused by the surgical insult were ultimately harmful.  Eventually, the need for blunting of the [[surgical stress]] response was identified by [[Harvey Williams Cushing|Harvey Cushing]], who injected local anesthetic prior to [[hernia repair]]s.<ref name="Miller 2010" />{{rp|30}} This led to the development of other drugs that could blunt the response, leading to lower surgical [[mortality rate]]s.

The most common approach to reach the endpoints of [[general anesthesia]] is through the use of inhaled general anesthetics.  Each anesthetic has its own potency, which is correlated to its solubility in oil. This relationship exists because the drugs bind directly to cavities in proteins of the central nervous system, although several [[theories of general anaesthetic action|theories of general anesthetic action]] have been described. Inhalational anesthetics are thought to exact their effects on different parts of the central nervous system.  For instance, the [[paralysis|immobilizing]] effect of inhaled anesthetics results from an effect on the [[spinal cord]] whereas sedation, hypnosis and amnesia involve sites in the brain.<ref name="Miller 2010" />{{rp|515}}  The potency of an inhalational anesthetic is quantified by its [[minimum alveolar concentration]] (MAC).  The MAC is the percentage dose of anesthetic that will prevent a response to painful stimulus in 50% of subjects.  The higher the MAC, generally, the less potent the anesthetic.

[[File:Anesthesia medications.JPG|thumb|[[Syringe]]s prepared with medications that are expected to be used during an operation under general anesthesia maintained by [[sevoflurane]] gas:
<br>– [[Propofol]], a hypnotic
<br>– [[Ephedrine]], in case of [[hypotension]]
<br>– [[Fentanyl]], for [[analgesia]]
<br>– [[Atracurium]], for [[neuromuscular-blocking drug|neuromuscular blockade]]
<br>– [[Glycopyrronium bromide]] (here under trade name "Robinul"), reducing secretions
]]
The ideal anesthetic drug would provide hypnosis, amnesia, analgesia, and muscle relaxation without undesirable changes in blood pressure, pulse or breathing.  In the 1930s, physicians started to augment inhaled general anesthetics with [[injectable|intravenous]] general anesthetics.  The drugs used in combination offered a better risk profile to the subject under anesthesia and a quicker recovery.  A combination of drugs was later shown to result in lower odds of dying in the first seven days after anesthetic. For instance, [[propofol]] (injection) might be used to start the anesthetic, [[fentanyl]] (injection) used to blunt the stress response, [[midazolam]] (injection) given to ensure amnesia and [[sevoflurane]] (inhaled) during the procedure to maintain the effects.  More recently, several intravenous drugs have been developed which, if desired, allow inhaled general anesthetics to be avoided completely.<ref name="Miller 2010" />{{rp|720}}

==== Equipment ====
{{Further|Instruments used in anesthesiology|Anaesthetic machine}}

The core instrument in an inhalational anesthetic delivery system is an [[anesthetic machine]]. It has [[anesthetic vaporizer|vaporizer]]s, [[medical ventilator|ventilator]]s, an anesthetic breathing circuit, waste gas scavenging system and pressure gauges. The purpose of the anesthetic machine is to provide anesthetic gas at a constant pressure, oxygen for breathing and to remove carbon dioxide or other waste anesthetic gases. Since inhalational anesthetics are flammable, various checklists have been developed to confirm that the machine is ready for use, that the safety features are active and the electrical hazards are removed.<ref name="Machine_checklist">{{cite journal | vauthors = Goneppanavar U, Prabhu M | title = Anaesthesia machine: checklist, hazards, scavenging | journal = Indian Journal of Anaesthesia | volume = 57 | issue = 5 | pages = 533–40 | date = September 2013 | pmid = 24249887 | pmc = 3821271 | doi = 10.4103/0019-5049.120151 | doi-access = free }}</ref> [[Intravenous]] anesthetic is delivered either by [[Bolus (medicine)|bolus]] doses or an [[infusion pump]]. There are also many smaller instruments used in [[airway management]] and monitoring the patient. The common thread to [[Certified Registered Nurse Anesthetist|modern machinery]] in this field is the use of [[fail-safe]] systems that decrease the odds of catastrophic misuse of the machine.<ref name="Machine_safety">{{cite journal | vauthors = Subrahmanyam M, Mohan S | title = Safety features in anaesthesia machine | journal = Indian Journal of Anaesthesia | volume = 57 | issue = 5 | pages = 472–80 | date = September 2013 | pmid = 24249880 | pmc = 3821264 | doi = 10.4103/0019-5049.120143 | doi-access = free }}</ref>

==== Monitoring ====
[[File:Maquet Flow-I anesthesia machine.jpg|thumb|An [[anesthetic machine]] with integrated systems for [[monitoring (medicine)|monitoring]] of several vital parameters]]
Patients under general anesthesia must undergo continuous physiological [[monitoring (medicine)|monitoring]] to ensure safety. In the US, the [[American Society of Anesthesiologists]] (ASA) has established minimum monitoring guidelines for patients receiving general anesthesia, regional anesthesia, or sedation. These include electrocardiography (ECG), heart rate, blood pressure, inspired and expired gases, oxygen saturation of the blood (pulse oximetry), and temperature.<ref name=ASAHQ>[https://web.archive.org/web/20120107122507/https://asahq.org/For-Members/~/media/For%20Members/documents/Standards%20Guidelines%20Stmts/Basic%20Anesthetic%20Monitoring%202011.ashx Standards for Basic Anesthetic Monitoring]. Committee of Origin: Standards and Practice Parameters (Approved by the ASA House of Delegates on 21 October 1986, amended 20 October 2010 with an effective date of 1 July 2011)</ref> In the UK the Association of Anaesthetists (AAGBI) have set minimum monitoring guidelines for general and regional anesthesia. For minor surgery, this generally includes monitoring of [[heart rate]], [[oxygen saturation]], [[blood pressure]], and inspired and expired concentrations for [[oxygen]], [[carbon dioxide]], and inhalational anesthetic agents. For more invasive surgery, monitoring may also include temperature, urine output, blood pressure, [[central venous pressure]], [[pulmonary artery pressure]] and [[pulmonary wedge pressure|pulmonary artery occlusion pressure]], [[cardiac output]], [[Bispectral index|cerebral activity]], and neuromuscular function. In addition, the operating room environment must be monitored for ambient temperature and humidity, as well as for accumulation of exhaled inhalational anesthetic agents, which might be deleterious to the health of operating room personnel.<ref name="AAGBI_Monitoring">{{cite conference | url=http://www.aagbi.org/sites/default/files/standardsofmonitoring07.pdf | title=Recommendations for Standards of Monitoring During Anaesthesia and Recovery 4th Edition | publisher=Association of Anaesthetists of Great Britain and Ireland | access-date=21 February 2014 | editor=Birks RJS | date=March 2007 | archive-url=https://web.archive.org/web/20150513045417/http://www.aagbi.org/sites/default/files/standardsofmonitoring07.pdf | archive-date=13 May 2015 | url-status=dead }}</ref>