View source for Anesthesia

{{Short description|State of medically-controlled temporary loss of sensation or awareness}}
{{Hatnote group|{{distinguish|paresthesia|anesthetic}}{{for multi|the medical speciality|Anesthesiology|other uses}}}}
{{More citations needed|date=July 2022}}
{{Use dmy dates|date=October 2020}}
{{Use American English|date = January 2019}}
{{Infobox medical intervention
| name         = Anesthesia<br/>Anaesthesia
| image        = [[File:Preoxygenation before anesthetic induction.jpg|300px]]
| caption        = A child preparing to go under anesthesia
| pronounce    = {{IPAc-en|ˌ|æ|n|ɪ|s|ˈ|θ|iː|z|i|ə|,_|-|s|i|ə|,_|-|ʒ|ə}}<ref>{{Cite OED|anaesthesia}}</ref>
| ICD10        =
| ICD9         =
| ICD9unlinked =
| MeshID       = E03.155
| LOINC        =
| other_codes  =
| MedlinePlus  = anesthesia
| eMedicine    = 1271543
}}

'''Anesthesia''' ([[American English]]) or '''anaesthesia''' ([[British English]]) is a state of controlled, temporary loss of sensation or awareness that is induced for medical or veterinary purposes. It may include some or all of [[analgesia]] (relief from or prevention of [[pain]]), [[paralysis]] (muscle relaxation), [[amnesia]] (loss of memory), and [[unconsciousness]]. An individual under the effects of [[anesthetic]] drugs is referred to as being anesthetized.

Anesthesia enables the painless performance of procedures that would otherwise require [[physical restraint]] in a non-anesthetized individual, or would otherwise be technically unfeasible. Three broad categories of anesthesia exist:
* ''[[General anesthesia]]'' suppresses [[central nervous system]] activity and results in unconsciousness and total lack of [[Sensation (psychology)|sensation]], using either injected or inhaled drugs.
* ''[[Sedation]]'' suppresses the central nervous system to a lesser degree, inhibiting both [[anxiolysis|anxiety]] and creation of [[long-term memory|long-term memories]] without resulting in unconsciousness.
* ''[[Local anesthesia|Regional and local anesthesia]]''  block transmission of nerve impulses from a specific part of the body. Depending on the situation, this may be used either on its own (in which case the individual remains fully conscious), or in combination with general anesthesia or sedation.
**''Local anesthesia'' is simple infiltration by the clinician directly onto the region of interest (e.g. numbing a tooth for dental work).
** ''Peripheral [[nerve block]]s'' use drugs targeted at [[peripheral nervous system|peripheral nerves]] to anesthetize an isolated part of the body, such as an entire limb.
** ''[[Neuraxial blockade]]'', mainly [[epidural anaesthesia|epidural]] and [[spinal anaesthesia|spinal]] anesthesia, can be performed in the region of the central nervous system itself, suppressing all incoming sensation from nerves supplying the area of the block.

In preparing for a medical or veterinary procedure, the clinician chooses one or more drugs to achieve the types and degree of anesthesia characteristics appropriate for the type of procedure and the particular patient. The types of drugs used include [[general anaesthetic|general anesthetics]], [[local anesthetic]]s, [[hypnotic]]s, [[dissociative]]s, [[sedative]]s, [[adjunct therapy|adjuncts]], [[neuromuscular-blocking drug]]s, [[narcotic]]s, and [[analgesic]]s.

The risks of complications during or after anesthesia are often difficult to separate from those of the procedure for which anesthesia is being given, but in the main they are related to three factors: the health of the individual, the complexity and stress of the procedure itself, and the anaesthetic technique. Of these factors, the individual's health has the greatest impact. Major [[perioperative]] risks can include [[death]], [[myocardial infarction|heart attack]], and [[pulmonary embolism]] whereas minor risks can include [[nausea|postoperative nausea and vomiting]] and [[hospital readmission]]. Some conditions, like local anesthetic toxicity, [[airway]] trauma or [[malignant hyperthermia]], can be more directly attributed to specific anesthetic drugs and techniques.

== Medical uses ==
<!--see Talk page on endpoints.  Discussed with expert; author of Miller's anesthesiology-->
The purpose of anesthesia can be distilled down to three basic goals or endpoints:<ref name="Miller 2010">{{Cite book|title=Miller's Anesthesia | edition = Seventh| vauthors = Miller RD |publisher=Churchill Livingstone Elsevier|year=2010|isbn=978-0-443-06959-8| veditors = Erikson LI, Fleisher LA, Wiener-Kronish JP, Young WL |location=US}}</ref>{{rp|236}}
* [[hypnotic|hypnosis]] (a temporary loss of [[consciousness]] and with it a loss of [[memory]].  In a pharmacological context, the word hypnosis usually has this technical meaning, in contrast to its more familiar lay or psychological meaning of an altered state of consciousness not necessarily caused by drugs—see [[hypnosis]]).
* [[analgesia]] (lack of sensation which also blunts [[Autonomic nervous system|autonomic reflexes]])
* [[Muscle relaxant|muscle relaxation]]

Different types of anesthesia affect the endpoints differently. [[Regional anesthesia]], for instance, affects analgesia; [[benzodiazepine]]-type sedatives (used for sedation, or "[[twilight anesthesia]]") favor [[amnesia]]; and [[general anesthesia|general anesthetics]] can affect all of the endpoints.  The goal of anesthesia is to achieve the endpoints required for the given surgical procedure with the least risk to the subject.
[[File:Operating room anesthetic station.jpg|thumb|right|The anesthetic area of an operating room]]
To achieve the goals of anesthesia, drugs act on different but interconnected parts of the nervous system. [[hypnotic|Hypnosis]], for instance, is generated through actions on the [[Nucleus (neuroanatomy)|nuclei in the brain]] and is similar to the activation of [[sleep]].  The effect is to make people less [[awareness|aware]] and less reactive to [[noxious stimulus|noxious stimuli]].<ref name="Miller 2010" />{{rp|245}}

Loss of [[memory]] ([[amnesia]]) is created by action of drugs on multiple (but specific) regions of the brain.  Memories are created as either [[Declarative memory|declarative]] or [[Procedural memory|non-declarative]] memories in several stages ([[Short-term memory|short-term]], [[Long-term memory|long-term]], [[Working memory|long-lasting]]) the strength of which is determined by the strength of connections between neurons termed [[synaptic plasticity]].<ref name="Miller 2010" />{{rp|246}} Each anesthetic produces amnesia through unique effects on memory formation at variable doses. [[Inhalational anesthetics]] will reliably produce amnesia through general suppression of the nuclei at doses below those required for loss of consciousness. Drugs like [[midazolam]] produce amnesia through different pathways by blocking the formation of long-term memories.<ref name="Miller 2010" />{{rp|249}}

Nevertheless, a person can [[dreams|dream]] under anesthesia or are conscious of the procedure despite giving no indication of this during it.  An estimated 22% of people do [[dream]] under [[general anesthesia]], and one or two cases in a thousand have some consciousness, termed "[[anesthesia awareness]]".<ref name="Miller 2010" />{{rp|253}} It is not known whether animals dream while under general anesthesia.

== Techniques ==
Anesthesia is not a direct treatment in its own right, but rather it facilitates other treatments, diagnoses, or cures which would otherwise be painful or complicated. The best anesthetic, therefore, is the one with the lowest risk to the patient while still achieving the endpoints required to complete the procedure. The first stage in anesthesia is pre-operative risk assessment consisting of the [[medical history]], [[physical examination]] and [[Medical test|lab tests]]. Diagnosing the patient's pre-operative physical status allows the clinician to minimize anesthetic risks.  A well completed medical history will arrive at the correct diagnosis 56% of the time which increases to 73% with a physical examination.  [[Medical test|Lab tests]] help in diagnosis but only in 3% of cases, underscoring the need for a full history and physical examination prior to anesthetics. Incorrect pre-operative assessments or preparations are the root cause of 11% of all adverse anesthetic events.<ref name="Miller 2010" />{{rp|1003}}

Safe anesthesia care depends greatly on well-functioning teams of highly trained healthcare workers. The [[medical specialty]] centred around anesthesia is called [[anesthesiology]], and doctors specialised in the field are termed anesthesiologists.<ref name="pmid29734240"/> Additional healthcare professionals involved in anesthesia provision have varying titles and roles depending on the jurisdiction, and include [[perioperative nurse|anesthetic nurses]], [[nurse anesthetist]]s, [[anesthesiologist assistant]]s, [[anaesthetic technician]]s, [[anaesthesia associate]]s, [[operating department practitioner]]s and [[anesthesia technologist]]s. International standards for the safe practice of anesthesia, jointly endorsed by the [[World Health Organization]] and the [[World Federation of Societies of Anaesthesiologists]], highly recommend that anesthesia should be provided, overseen or led by anesthesiologists, with the exception of minimal sedation or superficial procedures performed under local anesthesia.<ref name="pmid29734240">{{cite journal | vauthors = Gelb AW, Morriss WW, Johnson W, Merry AF, Abayadeera A, Belîi N, Brull SJ, Chibana A, Evans F, Goddia C, Haylock-Loor C, Khan F, Leal S, Lin N, Merchant R, Newton MW, Rowles JS, Sanusi A, Wilson I, Velazquez Berumen A | display-authors = 6 | title = World Health Organization-World Federation of Societies of Anaesthesiologists (WHO-WFSA) International Standards for a Safe Practice of Anesthesia | journal = Anesthesia and Analgesia | volume = 126 | issue = 6 | pages = 2047–55 | date = June 2018 | pmid = 29734240 | doi = 10.1213/ANE.0000000000002927 | url = https://escholarship.org/uc/item/8qj6d507 | s2cid = 13688396 | doi-access = free }}</ref>

A trained, vigilant anesthesia provider should continually care for the patient; where the provider is not an anesthesiologist, they should be locally directed and supervised by an anesthesiologist, and in countries or settings where this is not feasible, care should be led by the most qualified local individual within a regional or national anesthesiologist-led framework.<ref name="pmid29734240"/> The same minimum standards for [[patient safety]] apply regardless of the provider, including continuous clinical and biometric monitoring of tissue oxygenation, perfusion and blood pressure; confirmation of correct placement of [[airway management]] devices by [[auscultation]] and [[carbon dioxide]] detection; use of the [[WHO Surgical Safety Checklist]]; and safe onward transfer of the patient's care following the procedure.<ref name="pmid29734240" />

{| class="wikitable floatright" style="text-align:center;font-size:90%;width:45%;margin-left:1em"
|+ style="background:#E5AFAA;"|'''[[ASA physical status classification system]]'''<ref name="Henry2011" />
|- style="background: #E5AFAA;text-align:center;font-size:90%;"
! abbr="Class" | ASA class
! abbr="Description" | Physical status
|-
| ASA 1
| Healthy person
|-
| ASA 2
| Mild [[systemic disease]]
|-
| ASA 3
| Severe systemic [[disease]]
|-
| ASA 4
| Severe systemic disease that is a constant threat to [[life]]
|-
| ASA 5
| A [[wikt:moribund|moribund]] person who is not expected to survive without the [[surgery|operation]]
|-
| ASA 6
| A declared [[brain-dead]] person whose [[Organ (anatomy)|organs]] are being removed for [[Organ donation|donor]] purposes
|-
| E
| Suffix added for patients undergoing emergency procedure
|}
One part of the [[Risk management|risk assessment]] is based on the patient's health.  The American Society of Anesthesiologists has developed a six-tier scale that stratifies the patient's pre-operative physical state.  It is called the [[ASA physical status classification system|ASA physical status classification]]. The scale assesses risk as the patient's general health relates to an anesthetic.<ref name="Henry2011">{{cite journal | vauthors = Fitz-Henry J | title = The ASA classification and peri-operative risk | journal = Annals of the Royal College of Surgeons of England | volume = 93 | issue = 3 | pages = 185–87 | date = April 2011 | pmid = 21477427 | pmc = 3348554 | doi = 10.1308/rcsann.2011.93.3.185a }}</ref>

The more detailed [[Preanesthetic assessment|pre-operative]] [[medical history]] aims to discover genetic disorders (such as [[malignant hyperthermia]] or [[pseudocholinesterase deficiency]]), habits ([[smoking|tobacco]], [[drug abuse|drug]] and [[Alcohol dependence|alcohol use]]), physical attributes (such as [[obesity]] or a difficult [[airway]]) and any coexisting diseases (especially [[Cardiovascular disease|cardiac]] and [[Chronic obstructive pulmonary disease|respiratory diseases]]) that might impact the anesthetic.  The [[Preanesthetic assessment|preanesthetic]] [[physical examination]] helps quantify the impact of anything found in the medical history in addition to lab tests.<ref name="Miller 2010" />{{rp|1003–09}}

Aside from the generalities of the patient's health assessment, an evaluation of specific factors as they relate to the surgery also need to be considered for anesthesia.  For instance, anesthesia during [[childbirth]] must consider not only the mother but the baby.  [[Cancer]]s and [[tumor]]s that occupy the lungs or [[airway|throat]] create special challenges to [[general anesthesia]].  After determining the health of the patient undergoing anesthesia and the endpoints that are required to complete the procedure, the type of anesthetic can be selected. Choice of surgical method and anesthetic technique aims to reduce risk of complications, shorten time needed for recovery and minimize the [[surgical stress]] response.

=== 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>{{cite web |url=https://asahq.org/For-Members/~/media/For%20Members/documents/Standards%20Guidelines%20Stmts/Basic%20Anesthetic%20Monitoring%202011.ashx |title=Standards for Basic Anesthetic Monitoring |publisher=Committee of Origin: Standards and Practice Parameters |archive-url=https://web.archive.org/web/20120107122507/https://asahq.org/For-Members/~/media/For%20Members/documents/Standards%20Guidelines%20Stmts/Basic%20Anesthetic%20Monitoring%202011.ashx |archive-date=7 January 2012 |id=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 }}</ref>

=== Sedation ===
{{Further|Sedation}}
Sedation (also referred to as ''dissociative anesthesia'' or ''twilight anesthesia'') creates [[Hypnotic state|hypnotic]], [[sedation|sedative]], [[anxiolytic]], [[amnesic]], [[anticonvulsant]], and centrally produced muscle-relaxing properties.  From the perspective of the person giving the sedation, the patient appears sleepy, relaxed and forgetful, allowing unpleasant procedures to be more easily completed.  Sedatives such as [[benzodiazepine]]s are usually given with pain relievers (such as [[narcotics]], or [[local anesthetics]] or both) because they do not, by themselves, provide significant [[analgesic|pain relief]].<ref name="Reddy">{{cite journal | vauthors = Reddy S, Patt RB | title = The benzodiazepines as adjuvant analgesics | journal = Journal of Pain and Symptom Management | volume = 9 | issue = 8 | pages = 510–14 | date = November 1994 | pmid = 7531735 | doi = 10.1016/0885-3924(94)90112-0 | doi-access = free }}</ref>

From the perspective of the subject receiving a sedative, the effect is a feeling of general relaxation, amnesia (loss of memory) and time passing quickly.  Many drugs can produce a sedative effect including [[benzodiazepine]]s, [[propofol]], [[thiopental]], [[ketamine]] and inhaled general anesthetics.  The advantage of sedation over a general anesthetic is that it generally does not require support of the airway or breathing (no [[tracheal intubation]] or [[mechanical ventilation]]) and can have less of an effect on the [[cardiovascular system]] which may add to a greater margin of safety in some patients.<ref name="Miller 2010" />{{rp|736}}

=== Regional anesthesia ===
{{Further|Conduction anesthesia}}
{{multiple image
| align     = right
| direction = vertical
| width     = 180

| image1    = Fermoral nerve block.jpg
| caption1  = Sonography guided femoral nerve block

| image2    = Liquor bei Spinalanaesthesie.JPG
| caption2  = Backflow of [[cerebrospinal fluid]] through a spinal needle after puncture of the [[arachnoid mater]] during spinal anesthesia
}}

When pain is blocked from a part of the body using [[local anesthetics]], it is generally referred to as regional anesthesia. There are many types of regional anesthesia either by injecting into the tissue itself, a vein that feeds the area or around a nerve trunk that supplies sensation to the area. The latter are called nerve blocks and are divided into peripheral or central nerve blocks.

The following are the types of regional anesthesia:<ref name="Miller 2010" />{{rp|926–31}}
* ''Infiltrative anesthesia'': a small amount of local anesthetic is injected in a small area to stop any sensation (such as during the closure of a [[laceration]], as a [[Continuous wound infiltration|continuous infusion]] or "freezing" a tooth).  The effect is almost immediate.
* ''[[Nerve block|Peripheral nerve block]]'': local anesthetic is injected near a nerve that provides sensation to particular portion of the body.  There is significant variation in the speed of onset and duration of anesthesia depending on the potency of the drug (e.g. [[Inferior alveolar nerve anaesthesia|Mandibular block]], [[Fascia Iliaca Compartment Block]]<ref name="Mallinson2019">{{cite journal |last1=Mallinson |first1=Tom |title=Fascia iliaca compartment block: a short how-to guide |journal=Journal of Paramedic Practice |date=2 April 2019 |volume=11 |issue=4 |pages=154–155 |doi=10.12968/jpar.2019.11.4.154 |s2cid=145859649 }}</ref>).
* ''[[Intravenous regional anesthesia]]'' (also called a [[Bier block]]): dilute local anesthetic is infused to a limb through a vein with a [[tourniquet]] placed to prevent the drug from diffusing out of the limb.
* ''Central nerve block'': Local anesthetic is injected or infused in or around a portion of the central nervous system (discussed in more detail below in spinal, epidural and caudal anesthesia).
* ''[[Topical anesthetic|Topical anesthesia]]'': local anesthetics that are specially formulated to diffuse through the mucous membranes or skin to give a thin layer of analgesia to an area (e.g. [[Lidocaine/prilocaine|EMLA patches]]).
* ''[[Tumescent anesthesia]]'': a large amount of very dilute local anesthetics are injected into the [[subcutaneous tissue]]s during liposuction.
* ''Systemic local anesthetics'': local anesthetics are given systemically (orally or intravenous) to relieve [[neuropathic pain]]. 
A 2018 Cochrane review found moderate quality evidence that regional anesthesia may reduce the frequency of [[persistent postoperative pain]] (PPP) from 3 to 18 months following [[thoracotomy]] and 3 to 12 months following [[Caesarean section|caesarean]].<ref name="Weinstein-2018">{{Cite journal|vauthors=Weinstein EJ, Levene JL, Cohen MS, Andreae DA, Chao JY, Johnson M, Hall CB, Andreae MH|date=20 Jun 2018|title=Local anaesthetics and regional anaesthesia versus conventional analgesia for preventing persistent postoperative pain in adults and children|url=|journal=Cochrane Database Syst Rev|volume=6|issue=2|article-number=CD007105|doi=10.1002/14651858.CD007105.pub4|pmid=29926477|pmc=6377212}}</ref> Low quality evidence was found 3 to 12 months following breast cancer surgery.<ref name="Weinstein-2018" />  This review acknowledges certain limitations that impact its applicability beyond the surgeries and regional anesthesia techniques reviewed.<ref name="Weinstein-2018" />

==== Nerve blocks ====
{{Further|Nerve block}}
When [[local anesthetic]] is injected around a larger diameter nerve that transmits sensation from an entire region it is referred to as a [[nerve block]] or regional nerve blockade.  Nerve blocks are commonly used in dentistry, when the [[mandibular nerve]] is blocked for procedures on the lower teeth.  With larger diameter nerves (such as the [[scalene muscles|interscalene]] block for upper limbs or [[Psoas major muscle|psoas compartment]] block for lower limbs) the nerve and position of the needle is localized with [[Medical ultrasonography|ultrasound]] or electrical stimulation. Evidence supports the use of ultrasound guidance alone, or in combination with peripheral nerve stimulation, as superior for improved sensory and motor block, a reduction in the need for supplementation and fewer complications.<ref>{{cite journal |last1=Lewis |first1=Sharon R |last2=Price |first2=Anastasia |last3=Walker |first3=Kevin J |last4=McGrattan |first4=Ken |last5=Smith |first5=Andrew F |title=Ultrasound guidance for upper and lower limb blocks |journal=Cochrane Database of Systematic Reviews |date=11 September 2015 |volume=2015 |issue=9 |article-number=CD006459 |doi=10.1002/14651858.CD006459.pub3 |pmid=26361135 |pmc=6465072 }}</ref>  Because of the large amount of local anesthetic required to affect the nerve, the maximum dose of local anesthetic has to be considered.  Nerve blocks are also used as a continuous infusion, following major surgery such as knee, hip and shoulder replacement surgery, and may be associated with lower complications.<ref name="Ullah">{{cite journal | vauthors = Ullah H, Samad K, Khan FA | title = Continuous interscalene brachial plexus block versus parenteral analgesia for postoperative pain relief after major shoulder surgery | journal = The Cochrane Database of Systematic Reviews | issue = 2 | article-number = CD007080 | date = February 2014 | volume = 2014 | pmid = 24492959 | pmc = 7182311 | doi = 10.1002/14651858.CD007080.pub2 }}</ref> Nerve blocks are also associated with a lower risk of neurologic complications compared to the more central epidural or spinal neuraxial blocks.<ref name="Miller 2010" />{{rp|1639–41}}

==== Spinal, epidural and caudal anesthesia ====
{{Further|Neuraxial blockade|History of neuraxial anesthesia}}

[[Neuraxial blockade|Central neuraxial anesthesia]] is the injection of [[local anesthetic]] around the [[spinal cord]] to provide analgesia in the [[abdomen]], [[human pelvis|pelvis]] or [[Human leg|lower extremities]].  It is divided into either spinal (injection into the [[subarachnoid space]]), epidural (injection outside of the subarachnoid space into the [[epidural]] space) and caudal (injection into the [[cauda equina]] or tail end of the spinal cord).  Spinal and epidural are the most commonly used forms of central neuraxial blockade.

[[Spinal anesthesia]] is a "one-shot" injection that provides rapid onset and profound sensory anesthesia with lower doses of anesthetic, and is usually associated with [[neuromuscular blockade]] (loss of muscle control). [[Epidural anesthesia]] uses larger doses of anesthetic infused through an indwelling catheter which allows the anesthetic to be augmented should the effects begin to dissipate. Epidural anesthesia does not typically affect muscle control.

Because central neuraxial blockade causes [[arterial]] and [[venous]] [[vasodilation]], a drop in [[blood pressure]] is common. This drop is largely dictated by the venous side of the [[circulatory system]] which holds 75% of the circulating [[blood volume]].  The physiologic effects are much greater when the block is placed above the 5th [[thoracic vertebrae|thoracic vertebra]].  An ineffective block is most often due to inadequate [[anxiolysis]] or [[sedation]] rather than a failure of the block itself.<ref name="Miller 2010" />{{rp|1611}}

=== Acute pain management ===
[[File:PCA-01.JPG|thumb|180px|right|A patient-controlled analgesia [[infusion pump]], configured for [[epidural]] administration of [[fentanyl]] and [[bupivacaine]] for postoperative [[analgesia]]]]
[[Nociception]] (pain sensation) is not hard-wired into the body.  Instead, it is a dynamic process wherein persistent painful stimuli can sensitize the system and either make pain management difficult or promote the development of chronic pain. For this reason, preemptive acute pain management may reduce both acute and chronic pain and is tailored to the surgery, the environment in which it is given (in-patient/out-patient) and the individual.<ref name="Miller 2010" />{{rp|2757}}

Pain management is classified into either pre-emptive or on-demand.  On-demand pain medications typically include either [[opioid]] or [[non-steroidal anti-inflammatory drugs]] but can also make use of novel approaches such as inhaled [[nitrous oxide]]<ref name="Klomp">{{cite journal | vauthors = Klomp T, van Poppel M, Jones L, Lazet J, Di Nisio M, Lagro-Janssen AL | title = Inhaled analgesia for pain management in labour | journal = The Cochrane Database of Systematic Reviews | volume = 12 | issue = 9 | article-number = CD009351 | date = September 2012 | pmid = 22972140 | doi = 10.1002/14651858.CD009351.pub2 | hdl-access = free | hdl = 1871/48559 | pmc = 11627147 }}</ref> or [[ketamine]].<ref>{{cite journal | vauthors = Radvansky BM, Shah K, Parikh A, Sifonios AN, Le V, Eloy JD | title = Role of ketamine in acute postoperative pain management: a narrative review | journal = BioMed Research International | volume = 2015 | article-number = 749837 | date = 2015-10-01 | pmid = 26495312 | pmc = 4606413 | doi = 10.1155/2015/749837 | doi-access = free }}</ref> On demand drugs can be administered by a clinician ("as needed drug orders") or by the patient using [[patient-controlled analgesia]] (PCA).  PCA has been shown to provide slightly better pain control and increased patient satisfaction when compared with conventional methods.<ref name="Hudcova">{{cite journal | vauthors = McNicol ED, Ferguson MC, Hudcova J | title = Patient controlled opioid analgesia versus non-patient controlled opioid analgesia for postoperative pain | journal = The Cochrane Database of Systematic Reviews | issue = 6 | article-number = CD003348 | date = June 2015 | volume = 2020 | pmid = 26035341 | pmc = 7387354 | doi = 10.1002/14651858.CD003348.pub3 }}</ref> Common preemptive approaches include epidural neuraxial blockade<ref name="Jones">{{cite journal | vauthors = Jones L, Othman M, Dowswell T, Alfirevic Z, Gates S, Newburn M, Jordan S, Lavender T, Neilson JP | display-authors = 6 | title = Pain management for women in labour: an overview of systematic reviews | journal = The Cochrane Database of Systematic Reviews | volume = 3 | issue = 3 | article-number = CD009234 | date = March 2012 | pmid = 22419342 | pmc = 7132546 | doi = 10.1002/14651858.CD009234.pub2 }}</ref> or nerve blocks.<ref name="Klomp"/> One review which looked at pain control after [[Aortic aneurysm|abdominal aortic surgery]] found that epidural blockade provides better pain relief (especially during movement) in the period up to three postoperative days. It reduces the duration of postoperative [[tracheal intubation]] by roughly half. The occurrence of prolonged postoperative [[mechanical ventilation]] and [[myocardial infarction]] is also reduced by epidural analgesia.<ref name="pmid26731032">{{cite journal | vauthors = Guay J, Kopp S | title = Epidural pain relief versus systemic opioid-based pain relief for abdominal aortic surgery | journal = The Cochrane Database of Systematic Reviews | issue = 1 | article-number = CD005059 | date = January 2016 | volume = 2017 | pmid = 26731032 | pmc = 6464571 | doi = 10.1002/14651858.CD005059.pub4 }}</ref>

== Risks and complications ==
{{See also|Patient safety}}
Risks and complications as they relate to anesthesia are classified as either [[Disease|morbidity]] (a disease or disorder that results from anesthesia) or [[Perioperative mortality|mortality]] (death that results from anesthesia).  Quantifying how anesthesia contributes to morbidity and mortality can be difficult because the patient's health prior to surgery and the complexity of the surgical procedure can also contribute to the risks.
[[File:Mortality rates by ASA status from Anesthesiology, V 97, No 6, Dec 2002 p1615.png|thumb|Anesthesia-related deaths by [[ASA physical status classification system|ASA status]]<ref name="Lagasse" />]]
Prior to the introduction of anesthesia in the early 19th century, the [[Stress (physiology)|physiologic stress]] from surgery caused significant complications and many deaths from [[Shock (circulatory)|shock]].  The faster the surgery was, the lower the rate of complications (leading to reports of very quick amputations).  The advent of anesthesia allowed more complicated and life-saving surgery to be completed, decreased the physiologic stress of the surgery, but added an element of risk.  It was two years after the introduction of ether anesthetics that the first death directly related to the use of anesthesia was reported.<ref name="Chaloner">{{cite journal | vauthors = Chaloner EJ, Flora HS, Ham RJ | title = Amputations at the London Hospital 1852–1857 | journal = Journal of the Royal Society of Medicine | volume = 94 | issue = 8 | pages = 409–12 | date = August 2001 | pmid = 11461989 | pmc = 1281639 | doi = 10.1177/014107680109400812 }}</ref>

Morbidity can be major ([[myocardial infarction]], [[pneumonia]], [[pulmonary embolism]], [[kidney failure]]/[[chronic kidney disease]], postoperative [[cognitive dysfunction]] and [[Allergic reactions to anaesthesia|allergy]]) or minor (minor [[nausea]], vomiting, readmission).  There is usually overlap in the contributing factors that lead to morbidity and mortality between the health of the patients, the type of surgery being performed and the anesthetic.  To understand the [[relative risk]] of each contributing factor, consider that the rate of deaths totally attributed to the patient's health is 1:870.  Compare that to the rate of deaths totally attributed to surgical factors (1:2860) or anesthesia alone (1:185,056) illustrating that the single greatest factor in anesthetic mortality is the health of the patient.  These statistics can also be compared to the first such study on mortality in anesthesia from 1954, which reported a rate of death from all causes at 1:75 and a rate attributed to anesthesia alone at 1:2680.<ref name="Miller 2010" />{{rp|993}}  Direct comparisons between mortality statistics cannot reliably be made over time and across countries because of differences in the stratification of risk factors, however, there is evidence that anesthetics have made a significant improvement in safety<ref name="Braz">{{cite journal | vauthors = Braz LG, Braz DG, Cruz DS, Fernandes LA, Módolo NS, Braz JR | title = Mortality in anesthesia: a systematic review | journal = Clinics | volume = 64 | issue = 10 | pages = 999–1006 | date = Oct 2009 | pmid = 19841708 | pmc = 2763076 | doi = 10.1590/S1807-59322009001000011 }}</ref> but to what degree is uncertain.<ref name="Lagasse">{{cite journal | vauthors = Lagasse RS | title = Anesthesia safety: model or myth? A review of the published literature and analysis of current original data | journal = Anesthesiology | volume = 97 | issue = 6 | pages = 1609–17 | date = December 2002 | pmid = 12459692 | doi = 10.1097/00000542-200212000-00038 | s2cid = 32903609 | doi-access = free }}</ref>

Rather than stating a flat rate of morbidity or mortality, many factors are reported as contributing to the relative risk of the procedure and anesthetic combined.  For instance, an operation on a person who is between the ages of 60–79 years old places the patient at 2.3 times greater risk than someone less than 60 years old.  Having an ASA score of 3, 4 or 5 places the person at 10.7 times greater risk than someone with an ASA score of 1 or 2.  Other variables include age greater than 80 (3.3 times risk compared to those under 60), gender (females have a lower risk of 0.8), urgency of the procedure (emergencies have a 4.4 times greater risk), experience of the person completing the procedure (less than 8 years experience and/or less than 600 cases have a 1.1 times greater risk) and the type of anesthetic (regional anesthetics are lower risk than general anesthetics).<ref name="Miller 2010" />{{rp|984}} [[Obstetrical]], the very young and the very old are all at greater risk of complication so extra precautions may need to be taken.<ref name="Miller 2010" />{{rp|969–86}}

On 14 December 2016, the Food and Drug Administration issued a Public Safety Communication warning that "repeated or lengthy use of general anesthetic and sedation drugs during surgeries or procedures in children younger than 3 years or in pregnant women during their third trimester may affect the development of children's brains."<ref>{{cite web |website=Food and Drug Administration |url=http://www.fda.gov/Drugs/DrugSafety/ucm532356.htm |title=FDA Drug Safety Communication: FDA review results in new warnings about using general anesthetics and sedation drugs in young children and pregnant women|date=14 December 2016 |archive-url=https://web.archive.org/web/20161217145533/http://www.fda.gov/Drugs/DrugSafety/ucm532356.htm |access-date=3 January 2017|archive-date=17 December 2016 }}</ref> The warning was criticized by the American College of Obstetricians and Gynecologists, which pointed out the absence of direct evidence regarding use in pregnant women and the possibility that "this warning could inappropriately dissuade providers from providing medically indicated care during pregnancy."<ref>{{cite web |website=American College of Obstetricians and Gynecologists |url=http://www.acog.org/About-ACOG/News-Room/Practice-Advisories/FDA-Warnings-Regarding-Use-of-General-Anesthetics-and-Sedation-Drugs |title=Practice Advisory: FDA Warnings Regarding Use of General Anesthetics and Sedation Drugs in Young Children and Pregnant Women |date= 21 December 2016 |access-date= 3 January 2017}}</ref> Patient advocates noted that a randomized clinical trial would be unethical, that the mechanism of injury is well-established in animals, and that studies had shown exposure to multiple uses of anesthetic significantly increased the risk of developing learning disabilities in young children, with a [[hazard ratio]] of 2.12 (95% confidence interval, 1.26–3.54).<ref>{{cite web |website=Kennerly Loutey |url=https://www.kennerlyloutey.com/anesthesia-pregnant-women-young-children/ |title=Anesthesia in Pregnant Women And Young Children: The FDA Versus ACOG |archive-url=https://web.archive.org/web/20180714153354/https://www.kennerlyloutey.com/anesthesia-pregnant-women-young-children/ |archive-date=14 July 2018 |access-date= 3 January 2017}}</ref>

== Recovery ==
The immediate time after anesthesia is called [[General anaesthesia#Emergence|emergence]].  Emergence from general anesthesia or sedation requires careful monitoring because there is still a risk of complication.<ref name="AAGBI_Recovery">{{cite journal | vauthors = Whitaker Chair DK, Booth H, Clyburn P, Harrop-Griffiths W, Hosie H, Kilvington B, Macmahon M, Smedley P, Verma R | display-authors = 6 | title = Immediate post-anaesthesia recovery 2013: Association of Anaesthetists of Great Britain and Ireland | journal = Anaesthesia | volume = 68 | issue = 3 | pages = 288–97 | date = March 2013 | pmid = 23384257 | doi = 10.1111/anae.12146 | s2cid = 9519895 }}</ref> [[Nausea]] and vomiting are reported at 9.8% but will vary with the type of anesthetic and procedure.  There is a need for [[airway management|airway support]] in 6.8%, there can be [[urinary retention]] (more common in those over 50 years of age) and [[hypotension]] in 2.7%.  [[Hypothermia]], shivering and confusion are also common in the immediate post-operative period because of the lack of muscle movement (and subsequent lack of heat production) during the procedure.<ref name="Miller 2010" />{{rp|2707}} Furthermore, the rare manifestation in the post-anesthetic period may be the occurrence of functional neurological symptom disorder (FNSD).<ref>{{cite journal | last1=D'Souza | first1=Ryan S. | last2=Vogt | first2=Matthew N. P. | last3=Rho | first3=Edwin H. | title=Post-operative functional neurological symptom disorder after anesthesia | journal=Bosnian Journal of Basic Medical Sciences | volume=20 | issue=3 | date=2020-08-03 | issn=1840-4812 | pmid=32070267 | pmc=7416177 | doi=10.17305/bjbms.2020.4646 | doi-access=free | pages=381–388 | url=https://www.bjbms.org/ojs/index.php/bjbms/article/download/4646/1306 }}</ref>

[[Postoperative cognitive dysfunction]] (also known as ''POCD'' and post-anesthetic confusion) is a disturbance in [[cognition]] after surgery.  It may also be variably used to describe [[emergence delirium]] (immediate post-operative confusion) and early cognitive dysfunction (diminished cognitive function in the first post-operative week).  Although the three entities (delirium, early POCD and long-term POCD) are separate, the presence of delirium post-operatively predicts the presence of early POCD.  There does not appear to be an association between delirium or early POCD and long-term POCD.<ref name="Rudolph2008">{{cite journal | vauthors = Rudolph JL, Marcantonio ER, Culley DJ, Silverstein JH, Rasmussen LS, Crosby GJ, Inouye SK | title = Delirium is associated with early postoperative cognitive dysfunction | journal = Anaesthesia | volume = 63 | issue = 9 | pages = 941–47 | date = September 2008 | pmid = 18547292 | pmc = 2562627 | doi = 10.1111/j.1365-2044.2008.05523.x }}</ref> According to a recent study conducted at the [[David Geffen School of Medicine at UCLA]], the brain navigates its way through a series of activity clusters, or "hubs" on its way back to consciousness. Andrew Hudson, an assistant professor in anesthesiology states, "Recovery from anesthesia is not simply the result of the anesthetic 'wearing off,' but also of the brain finding its way back through a maze of possible activity states to those that allow conscious experience. Put simply, the brain reboots itself."<ref>{{cite web | title=How brain 'reboots' itself to consciousness after anesthesia | website=ScienceDaily | date=2014-06-14 | url=https://www.sciencedaily.com/releases/2014/06/140618135834.htm }}</ref>

Long-term POCD is a subtle deterioration in cognitive function, that can last for weeks, months, or longer. Most commonly, relatives of the person report a lack of attention, memory and loss of interest in activities previously dear to the person (such as crosswords). In a similar way, people in the workforce may report an inability to complete tasks at the same speed they could previously.<ref name="Deiner">{{cite journal | vauthors = Deiner S, Silverstein JH | title = Postoperative delirium and cognitive dysfunction | journal = British Journal of Anaesthesia | volume = 103 | issue = Suppl 1 | pages = i41–46 | date = December 2009 | pmid = 20007989 | pmc = 2791855 | doi = 10.1093/bja/aep291 }}</ref> There is good evidence that POCD occurs after cardiac surgery and the major reason for its occurrence is the formation of [[Embolism|microemboli]]. POCD also appears to occur in non-cardiac surgery.  Its causes in non-cardiac surgery are less clear but older age is a risk factor for its occurrence.<ref name="Miller 2010" />{{rp|2805–16}}

== History ==
{{Main|History of general anesthesia|History of neuraxial anesthesia}}
{{See also|Hua Tuo}}
[[File:Statue of Hua Tuo in GDMU.jpg|thumb|right|A statue in Guangdong Medical University in honor of Hua Tuo]]
The first attempts at general anesthesia were probably [[herbalism|herbal remedies]] administered in [[prehistory]]. [[Ethanol|Alcohol]] is one of the oldest known [[sedative]]s and it was used in ancient [[Mesopotamia]] thousands of years ago.<ref name=Powell1996>{{cite book |title= The origins and ancient history of wine (Food and nutrition in history and anthropology) |edition=1 |volume=11 |chapter= Chapter 9: Wine and the vine in ancient Mesopotamia: the cuneiform evidence |pages= 96–124 |vauthors = Powell MA |veditors= McGovern PE, Fleming SJ, Katz SH |publisher= Gordon and Breach Publishers |location= Amsterdam |year=1996 |isbn=978-90-5699-552-2 |chapter-url= https://books.google.com/books?id=aXX2UcT_yw8C&pg=PA97 }}</ref> The Sumerians are said to have cultivated and harvested the [[opium]] poppy (''[[Papaver somniferum]]'') in lower Mesopotamia as early as 3400 [[BCE]].<ref name=Neligan1927>{{cite journal | vauthors = Evans TC |title= The opium question, with special reference to Persia (book review) |journal= Transactions of the Royal Society of Tropical Medicine and Hygiene |volume= 21 |pages= 339–40 |year= 1928 |doi= 10.1016/S0035-9203(28)90031-0 |quote= The earliest known mention of the poppy is in the language of the Sumerians, a non-Semitic people who descended from the uplands of Central Asia into Southern Mesopotamia&nbsp;... |issue= 4 }}</ref><ref name=Booth1996>{{cite book |title=Opium: A History |chapter=The discovery of dreams |page=[https://archive.org/details/opiumhistory00boot/page/15 15] | vauthors = Booth M |publisher=Simon & Schuster, Ltd. |location=London |year=1996 |isbn=978-0-312-20667-3 |chapter-url=https://books.google.com/books?id=8XHV8JAoAi4C&q=Opium:+A+History |url=https://archive.org/details/opiumhistory00boot/page/15 }}</ref> The ancient Egyptians had some surgical instruments,<ref name="Ebers1889">{{cite book |title=Papyrus Ebers|edition=1 |volume=2 | vauthors = Stern LC | veditors=  Ebers G |publisher= Bei S. Hirzel |location= Leipzig |language= de |year= 1889 |oclc= 14785083 |url= https://archive.org/details/papyrusebersdie00ebergoog |access-date= 2010-09-18 |editor-link= Georg Ebers}}</ref><ref name="Pahor1992I">{{cite journal | vauthors = Pahor AL | title = Ear, nose and throat in ancient Egypt | journal = The Journal of Laryngology and Otology | volume = 106 | issue = 8 | pages = 677–87 | date = August 1992 | pmid = 1402355 | doi = 10.1017/S0022215100120560 | s2cid = 35712860 }}</ref> as well as crude analgesics and sedatives, including possibly an extract prepared from the [[Mandragora (genus)|mandrake]] fruit.<ref name="Sullivan1996">{{cite journal | vauthors = Sullivan R | title = The identity and work of the ancient Egyptian surgeon | journal = Journal of the Royal Society of Medicine | volume = 89 | issue = 8 | pages = 467–73 | date = August 1996 | pmid = 8795503 | pmc = 1295891 | doi = 10.1177/014107689608900813 }}</ref>

In China, [[Bian Que]] ([[Chinese character|Chinese]]: 扁鹊, [[Wade–Giles]]: ''Pien Ch'iao'', {{circa|300 BCE}}) was a legendary Chinese [[Internal medicine|internist]] and surgeon who reportedly used general anesthesia for surgical procedures.<ref>{{cite journal |last1=Guo |first1=Qulian |date=December 2004 |title=Anesthesia in mainland China: its past and present |journal= The Hong Kong College of Anaesthesiologists |volume=13 |issue=4 |page=4}}</ref> Despite this, it was the Chinese physician [[Hua Tuo]] whom historians considered the first verifiable historical figure to develop a type of mixture of anesthesia, though his recipe has yet to be fully discovered.<ref>{{cite book|last=Mair|first=Victor H.|author-link=Victor H. Mair|year=1994|chapter=The Biography of Hua-t'o from the "History of the Three Kingdoms"|title=The Columbia Anthology of Traditional Chinese Literature|editor=Victor H. Mair|publisher=Columbia University Press|pages=688–96}}</ref>

Throughout Europe, Asia, and the Americas, a variety of ''[[Solanum]]'' species containing potent [[tropane alkaloid]]s was used for anesthesia. In 13th-century Italy, [[Theodoric Borgognoni]] used similar mixtures along with opiates to induce unconsciousness, and treatment with the combined alkaloids proved a mainstay of anesthesia until the 19th century.  Local anesthetics were used in [[Inca civilization]] where [[Shamanism|shamans]] chewed [[coca]] leaves and performed operations on the skull while spitting into the wounds they had inflicted to anesthetize.<ref name=Ruetsch2001>{{cite journal | vauthors = Ruetsch YA, Böni T, Borgeat A | title = From cocaine to ropivacaine: the history of local anesthetic drugs | journal = Current Topics in Medicinal Chemistry | volume = 1 | issue = 3 | pages = 175–82 | date = August 2001 | pmid = 11895133 | doi = 10.2174/1568026013395335 }}</ref> [[Cocaine]] was later isolated and became the first effective local anesthetic.  It was first used in [[eye surgery]] in 1884 by [[Karl Koller (ophthalmologist)|Karl Koller]], at the suggestion of [[Sigmund Freud]].<ref name=Koller1884>{{cite journal| vauthors = Koller K |author-link=Karl Koller (ophthalmologist)|title=Über die Verwendung des Kokains zur Anästhesierung am Auge|trans-title=On the use of cocaine for anesthesia on the eye|language=de|journal=Wiener Medizinische Wochenschrift|volume=34|pages=1276–309|year=1884}}</ref> German surgeon [[August Bier]] (1861–1949) was the first to use cocaine for [[intrathecal]] anesthesia in 1898.<ref name=Bier1899>{{cite journal| vauthors = Bier A |author-link=August Bier|title=Versuche über cocainisirung des rückenmarkes|trans-title=Experiments on the cocainization of the spinal cord|language=de|journal=Deutsche Zeitschrift für Chirurgie|volume=51|issue=3–4|pages=361–69|year=1899|doi=10.1007/BF02792160|s2cid=41966814|url=https://zenodo.org/record/1428422}}</ref> Romanian surgeon Nicolae Racoviceanu-Piteşti (1860–1942) was the first to use [[opioid]]s for intrathecal analgesia; he presented his experience in Paris in 1901.<ref name=Brill2003>{{cite journal | vauthors = Brill S, Gurman GM, Fisher A | title = A history of neuraxial administration of local analgesics and opioids | journal = European Journal of Anaesthesiology | volume = 20 | issue = 9 | pages = 682–89 | date = September 2003 | pmid = 12974588 | doi = 10.1017/S026502150300111X | s2cid = 46735940 }}</ref>

The "soporific sponge" ("sleep sponge") used by Arabic physicians was introduced to Europe by the [[Schola Medica Salernitana|Salerno school of medicine]] in the late 12th century and by [[Ugo Borgognoni]] (1180–1258) in the 13th century. The sponge was promoted and described by Ugo's son and fellow surgeon, [[Theodoric Borgognoni]] (1205–1298). In this anesthetic method, a sponge was soaked in a dissolved solution of opium, [[mandrake|mandragora]], hemlock juice, and other substances. The sponge was then dried and stored; just before surgery the sponge was moistened and then held under the patient's nose. When all went well, the fumes rendered the individual unconscious.<ref>{{Cite journal |title=The Ancestors of Inhalational Anesthesia: The Soporific Sponges (XIth–XVIIth Centuries): How a Universally Recommended Medical Technique Was Abruptly Discarded |last1=Juvin |first1=Phillippe |last2=Desmonts |first2=Jean-Marie |url=https://pubs.asahq.org/anesthesiology/article/93/1/265/491/The-Ancestors-of-Inhalational-Anesthesia-The |date=July 2000 |access-date=2023-01-15 |journal=Anesthesiology |volume=93 |issue=1 |pages=265–269|doi=10.1097/00000542-200007000-00037 |pmid=10861170 |s2cid=4867308 |doi-access=free }}</ref>

[[File:Anaesthesia exhibition, 1946 Wellcome M0009908.jpg|thumb|Sir [[Humphry Davy]]'s ''Researches chemical and philosophical: chiefly concerning nitrous oxide'' (1800), pp. 556 and 557 (right), outlining potential anesthetic properties of [[nitrous oxide]] in relieving pain during surgery]]
The most famous anesthetic, [[Diethyl ether#history|ether]], may have been synthesized as early as the 8th century,<ref name=Barash>{{cite book | vauthors = Toski JA, Bacon DR, Calverley RK | chapter = The history of Anesthesiology |edition=4th |publisher=Lippincott Williams & Wilkins |year=2001 |isbn=978-0-7817-2268-1 |page=3 | veditors = Barash PG, Cullen BF, Stoelting RK | title = Clinical Anesthesia}}</ref><ref name=Lullus>{{cite book |vauthors = Hademenos GJ, Murphree S, Zahler K, Warner JM |title=McGraw-Hill's PCAT |publisher=McGraw-Hill |page=39 |url=https://books.google.com/books?id=8MwxkLP87IUC&pg=PA39 |isbn=978-0-07-160045-3 |date=2008}}</ref> but it took many centuries for its anesthetic importance to be appreciated, even though the 16th century physician and polymath [[Paracelsus]] noted that chickens made to breathe it not only fell asleep but also felt no pain. By the early 19th century, ether was being used by humans, but only as a [[recreational drug]].<ref name=Fenster2001>{{cite book| vauthors = Fenster JM |title=Ether Day: The Strange Tale of America's Greatest Medical Discovery and the Haunted Men Who Made It|publisher=HarperCollins|location=New York|year=2001|chapter=Power Struggle|pages=[https://archive.org/details/etherdaystranget00fens/page/106 106–16]|isbn=978-0-06-019523-6|chapter-url=https://archive.org/details/etherdaystranget00fens|url=https://archive.org/details/etherdaystranget00fens/page/106}}</ref>

Meanwhile, in 1772, English scientist [[Joseph Priestley]] discovered the gas [[nitrous oxide]]. Initially, people thought this gas to be lethal, even in small doses, like some other [[nitrogen oxide]]s. However, in 1799, British chemist and inventor [[Humphry Davy]] decided to find out by experimenting on himself. To his astonishment he found that nitrous oxide made him laugh, so he nicknamed it "laughing gas".<ref name="Davy">{{cite book| vauthors = Hardman JG |title=Oxford Textbook of Anaesthesia|date=2017|publisher=Oxford University Press|page=529}}</ref> In 1800 Davy wrote about the potential anesthetic properties of nitrous oxide in relieving pain during surgery, but nobody at that time pursued the matter any further.<ref name="Davy"/>

On 14 November 1804, [[Hanaoka Seishū]], a Japanese doctor, became the first person to successfully perform surgery using [[General anaesthesia|general anesthesia]].<ref>{{cite journal |last1=Izuo |first1=Masaru |title=Medical history: Seishu hanaoka and his success in breast cancer surgery under general anesthesia two hundred years ago |journal=Breast Cancer |date=November 2004 |volume=11 |issue=4 |pages=319–324 |doi=10.1007/BF02968037 |pmid=15604985 |s2cid=43428862 }}</ref> Hanaoka learned traditional Japanese medicine as well as [[Rangaku|Dutch-imported]] European surgery and Chinese medicine.  After years of research and experimentation, he finally developed a formula which he named tsūsensan (also known as mafutsu-san), which combined [[Datura stramonium|Korean morning glory]] and other herbs.<ref>{{cite journal |last1=Ogata |first1=Tomio |title=Seishu Hanaoka and his anaesthesiology and surgery |journal=Anaesthesia |date=November 1973 |volume=28 |issue=6 |pages=645–652 |doi=10.1111/j.1365-2044.1973.tb00549.x |pmid=4586362 |s2cid=31352880 }}</ref>

Hanaoka's success in performing this painless operation soon became widely known, and patients began to arrive from all parts of Japan. Hanaoka went on to perform many operations using tsūsensan, including resection of [[Malignancy|malignant]] [[tumor]]s, extraction of [[Urolithiasis|bladder stones]], and extremity amputations.<ref>{{cite book |last1=Hyodo |first1=M. |last2=Oyama |first2=T. |last3=Oyama |first3=Tsutomu |last4=Swerdlow |first4=Mark |title=The Pain Clinic IV: Proceedings of the Fourth International Symposium, Kyoto, Japan, 18-21 November 1990 |date=1992 |publisher=VSP |isbn=978-90-6764-147-0 }}{{pn|date=March 2024}}</ref> Before his death in 1835, Hanaoka performed more than 150 operations for breast cancer. However, this finding did not benefit the rest of the world until 1854 as the [[Sakoku|national isolation policy]] of the [[Tokugawa shogunate]] prevented Hanaoka's achievements from being publicized until after the isolation ended.<ref>{{cite journal |last1=Toby |first1=Ronald P. |title=Reopening the Question of Sakoku: Diplomacy in the Legitimation of the Tokugawa Bakufu |journal=Journal of Japanese Studies |date=1977 |volume=3 |issue=2 |pages=323–363 |doi=10.2307/132115 |jstor=132115 }}</ref> Nearly forty years would pass before [[Crawford Long]], who is titled as the inventor of modern anesthetics in the [[Western world|West]], used general anesthesia in [[Jefferson, Georgia]].<ref>{{cite journal |last1=Long |first1=C. W. |title=An Account of the First Use of Sulphuric Ether by Inhalation as an Anæsthetic in Surgical Operations |journal=Survey of Anesthesiology |date=December 1991 |volume=35 |issue=6 |page=375 |doi=10.1097/00132586-199112000-00049 |url=https://journals.lww.com/surveyanesthesiology/citation/1991/12000/an_account_of_the_first_use_of_sulphuric_ether_by.49.aspx |url-access=subscription }}</ref>

Long noticed that his friends felt no pain when they injured themselves while staggering around under the influence of diethyl ether. He immediately thought of its potential in surgery. Conveniently, a participant in one of those "ether frolics", a student named James Venable, had two small tumors he wanted excised. But fearing the pain of surgery, Venable kept putting the operation off. Hence, Long suggested that he have his operation while under the influence of ether. Venable agreed, and on 30 March 1842 he underwent a painless operation. However, Long did not announce his discovery until 1849.<ref name="Long1849">{{cite journal| vauthors = Long CW |author-link=Crawford Long|title=An account of the first use of Sulphuric Ether by Inhalation as an Anesthetic in Surgical Operations|journal=Southern Medical and Surgical Journal|volume=5|pages=705–13|year=1849}}</ref>
[[File:Southworth & Hawes - First etherized operation (re-enactment).jpg|thumb|right|Historic image of an early [[diethyl ether|ether]] operation conducted at Massachusetts General Hospital.  The daguerreotype was taken by Southworth & Hawes on July 3, 1847.]]
[[File:Ether inhaler, c. 1846, developed by William T. G. Morton - National Museum of American History - DSC06167.JPG|thumb|Morton's ether inhaler]]
[[Horace Wells]] conducted the first public demonstration of the inhalational anesthetic at the [[Massachusetts General Hospital]] in [[Boston]] in 1845. However, the [[nitrous oxide]] was improperly administered and the person cried out in [[pain]].<ref name="NMAH">{{cite web|url=http://americanhistory.si.edu/collections/object.cfm?key=35&objkey=113|title=Miniature Portrait of Horace Wells|publisher=National Museum of American History, Smithsonian Institution|access-date=2008-06-30}}</ref> On 16 October 1846, Boston dentist [[William T. G. Morton|William Thomas Green Morton]] gave a successful demonstration using [[diethyl ether]] to medical students at the same venue.<ref>{{cite web | vauthors = Morkel H | title=The painful story behind modern anesthesia | url=https://www.pbs.org/newshour/health/the-painful-story-behind-modern-anesthesia |publisher=pbs.org| date=16 October 2013 }}</ref> Morton, who was unaware of Long's previous work, was invited to the [[Massachusetts General Hospital]] to demonstrate his new technique for painless surgery. After Morton had induced anesthesia, surgeon [[John Collins Warren (surgeon, born 1778)|John Collins Warren]] removed a tumor from the neck of [[Edward Gilbert Abbott]]. This occurred in the surgical amphitheater now called the [[Ether Dome]]. The previously skeptical Warren was impressed and stated, "Gentlemen, this is no humbug." In a letter to Morton shortly thereafter, physician and writer [[Oliver Wendell Holmes Sr.]] proposed naming the state produced "anesthesia", and the procedure an "anesthetic".<ref name="Fenster2001"/>

Morton at first attempted to hide the actual nature of his anesthetic substance, referring to it as Letheon. He received a [[US patent]] for his substance, but news of the successful anesthetic spread quickly by late 1846. Respected surgeons in Europe including [[Robert Liston|Liston]], [[Johann Friedrich Dieffenbach|Dieffenbach]], [[Nikolay Ivanovich Pirogov|Pirogov]], and [[James Syme|Syme]] quickly undertook numerous operations with ether. An American-born physician, Boott, encouraged London dentist [[James Robinson (dentist)|James Robinson]] to perform a dental procedure on a Miss Lonsdale. This was the first case of an operator-anesthetist. On the same day, 19 December 1846, in Dumfries Royal Infirmary, Scotland, a Dr. Scott used ether for a surgical procedure.<ref>{{cite journal | vauthors = Baillie TW | title = The first European trial of anaesthetic ether: the Dumfries claim | journal = British Journal of Anaesthesia | volume = 37 | issue = 12 | pages = 952–57 | date = December 1965 | pmid = 5323141 | doi = 10.1093/bja/37.12.952 | doi-access = free }}</ref> The first use of anesthesia in the Southern Hemisphere took place in [[Launceston, Tasmania]], that same year. Drawbacks with ether such as excessive vomiting and its explosive [[flammability]] led to its replacement in England with [[chloroform]].{{citation needed|date=May 2019}}

Discovered in 1831 by an American physician Samuel Guthrie (1782–1848), and independently a few months later by Frenchman Eugène Soubeiran (1797–1859) and Justus von Liebig (1803–1873) in Germany, chloroform was named and chemically characterized in 1834 by Jean-Baptiste Dumas (1800–1884). In 1842, Dr [[Robert Mortimer Glover]] in London discovered the anaesthetic qualities of chloroform on laboratory animals.<ref>{{cite journal |last1=Defalque |first1=R. J. |last2=Wright |first2=A. J. |title=The short, tragic life of Robert M. Glover |journal=Anaesthesia |date=April 2004 |volume=59 |issue=4 |pages=394–400 |doi=10.1111/j.1365-2044.2004.03671.x |pmid=15023112 |s2cid=46428403 }}</ref>

In 1847, Scottish obstetrician [[James Young Simpson]] was the first to demonstrate the anesthetic properties of chloroform on humans and helped to popularize the drug for use in medicine.<ref name=eb>{{cite encyclopedia|title=Sir James Young Simpson|url=https://www.britannica.com/EBchecked/topic/545447/Sir-James-Young-Simpson-1st-Baronet|encyclopedia=Encyclopædia Britannica|access-date=23 August 2013}}</ref> This first supply came from local pharmacists, James Duncan and [[William Flockhart]], and its use spread quickly, with 750,000 doses weekly in Britain by 1895. Simpson arranged for Flockhart to supply [[Florence Nightingale]].<ref>{{Cite journal|last=Worlin|first=P. M.|date=1998|title=Duncan and Flockhart: the Story of Two Men and a Pharmacy|journal=Pharmaceutical Historian|volume=28| issue = 2 |pages=28–33|pmid=11620310}}</ref> Chloroform gained royal approval in 1853 when [[John Snow (physician)|John Snow]] administered it to [[Queen Victoria]] when she was in labor with  [[Prince Leopold, Duke of Albany|Prince Leopold]]. For the experience of child birth itself, chloroform met all the Queen's expectations; she stated it was "delightful beyond measure".<ref>{{cite news|title=Queen Victoria uses chloroform in childbirth, 1853|url=https://www.ft.com/content/1e2ce5d6-aad3-11dd-897c-000077b07658 |archive-url=https://ghostarchive.org/archive/20221210/https://www.ft.com/content/1e2ce5d6-aad3-11dd-897c-000077b07658 |archive-date=10 December 2022 |url-access=subscription|newspaper=Financial Times|date=28 November 2017}}</ref>  Chloroform was not without fault though. The first fatality directly attributed to chloroform administration was recorded on 28 January 1848 after the death of Hannah Greener.<ref>{{cite journal | vauthors = Wawersik J | title = [History of chloroform anesthesia] | journal = Anaesthesiologie und Reanimation | volume = 22 | issue = 6 | pages = 144–52 | date = 1997-01-01 | pmid = 9487785 }}</ref> This was the first of many deaths to follow from the untrained handling of chloroform. Surgeons began to appreciate the need for a trained anesthetist. The need, as Thatcher writes, was for an anesthetist to "(1) Be satisfied with the subordinate role that the work would require, (2) Make anesthesia their one absorbing interest, (3) not look at the situation of anesthetist as one that put them in a position to watch and learn from the surgeons technique (4) accept the comparatively low pay and (5) have the natural aptitude and intelligence to develop a high level of skill in providing the smooth anesthesia and relaxation that the surgeon demanded"<ref>{{Cite book| vauthors = Nagelhout J |title=Nurse Anesthesia|publisher=Elsevier|year=2018|isbn=978-0-323-44392-0|location=St. Louis Missouri|pages=2–4}}</ref> These qualities of an anesthetist were often found in submissive [[medical school|medical students]] and even members of the public.  More often, surgeons sought out nurses to provide anesthesia. By the time of the [[American Civil War|Civil War]], many nurses had been professionally trained with the support of surgeons.

John Snow of London published articles from May 1848 onwards "On Narcotism by the Inhalation of Vapours" in the London Medical Gazette.<ref>{{cite journal| vauthors = Zorab J |title=On Narcotism by the Inhalation of Vapours by John Snow MD|journal=Journal of the Royal Society of Medicine|date=June 1992|volume=85|issue=6|page=371|pmc=1293529}}</ref> Snow also involved himself in the production of equipment needed for the administration of [[inhalational anesthetics]], the forerunner of today's [[anaesthetic machine|anesthesia machines]].<ref>https://www.ncbi.nlm.nih.gov/books/NBK572060/</ref>

Alice Magaw, born in November 1860, is often referred to as "The Mother of Anesthesia". Her renown as the personal anesthesia provider for William and Charles Mayo was solidified by Mayo's own words in his 1905 article in which he described his satisfaction with and reliance on nurse anesthetists: "The question of anaesthesia is a most important one. We have regular anaesthetists [on] whom we can depend so that I can devote my entire attention to the surgical work." Magaw kept thorough records of her cases and recorded these anesthetics. In her publication reviewing more than 14,000 surgical anesthetics, Magaw indicates she successfully provided anesthesia without an anesthetic-related death. Magaw describes
in another article, "We have administered an anesthetic 1,092 times; ether alone 674 times; chloroform 245 times; ether and chloroform combined 173 times. I can report that out of this number, 1,092 cases, we have not had an accident". Magaw's records and outcomes created a legacy defining that the delivery of anesthesia by nurses would serve the surgical community without increasing the risks to patients. In fact, Magaw's outcomes would eclipse those of practitioners today.<ref>{{cite journal |last1=Goode |first1=Victoria |title=Alice Magaw: A Model for Evidence-Based Practice |journal=AANA Journal |date=February 2015 |volume=83 |issue=1 |pages=50–55 |pmid=25842634 |url=https://www.aana.com/docs/default-source/aana-journal-web-documents-1/alice-magaw-0215-pp50-55.pdf?sfvrsn=ccd848b1_4}}</ref>

The first comprehensive medical textbook on the subject, ''Anesthesia'', was authored in 1914 by anesthesiologist Dr. [[James Tayloe Gwathmey]] and the chemist Dr. [[Charles Baskerville]].<ref name="Cope-1993">{{cite journal | vauthors = Cope DK | title = James Tayloe Gwathmey: seeds of a developing specialty | journal = Anesthesia and Analgesia | volume = 76 | issue = 3 | pages = 642–47 | date = March 1993 | pmid = 8452281 | doi = 10.1213/00000539-199303000-00035 | s2cid = 7574462 }}</ref> This book served as the standard reference for the specialty for decades and included details on the history of anesthesia as well as the physiology and techniques of inhalation, rectal, intravenous, and spinal anesthesia.<ref name="Cope-1993" />

Of these first famous anesthetics, only nitrous oxide is still widely used today, with chloroform and ether having been replaced by safer but sometimes more expensive [[general anesthetic]]s, and cocaine by more effective [[local anesthetic]]s with less abuse potential.<ref>{{Cite web |title=Celebrating 75 years of Anaesthesia: our past, present and future {{!}} Association of Anaesthetists |url=https://anaesthetists.org/Home/Celebrating-75-years-of-Anaesthesia-our-past-present-and-future |access-date=2022-10-17 |website=anaesthetists.org}}</ref>

== Society and culture ==
<!--This section intentionally gives equal weight to MD and RN groups based on reading previous edits.  It has been shortened (since each group has a full articles on each group) to make this article more readable for the layperson trying to learn about anesthesia-->

{{Further|Anesthesia provision in the United States|Anesthesiologist|Nurse anesthetist}}

Almost all healthcare providers use anesthetic drugs to some degree, but most health professions have their own field of specialists in the field including medicine, nursing and dentistry.

[[Physician|Doctors]] specializing in [[anaesthesiology]], including perioperative care, development of an anesthetic plan, and the administration of anesthetics are known in the US as ''anesthesiologists'' and in the UK, Canada, Australia, and NZ as ''anaesthetists'' or ''anaesthesiologists''. All anesthetics in the UK, Australia, New Zealand, Hong Kong and Japan are administered by doctors. [[Nurse anesthetists]] also administer anesthesia in 109 nations.<ref name=IFNA>{{cite web| vauthors = McAuliffe MS, Henry B |title=Nurse anesthesia worldwide: practice, education and regulation|work=Downloads|publisher=International Federation of Nurse Anesthetists|location=Silver Spring, Maryland|year=2010|url=http://ifna-int.org/ifna/e107_files/downloads/Practice.pdf|access-date=2012-06-13}}</ref> In the US, 35% of anesthetics are provided by physicians in solo practice, about 55% are provided by anesthesia care teams (ACTs) with anesthesiologists medically directing certified registered nurse anesthetists (CRNAs) or anesthesiologist assistants, and about 10% are provided by CRNAs in solo practice.<ref name=IFNA/><ref name=Physician2007>{{cite journal | vauthors = Abenstein JP, Long KH, McGlinch BP, Dietz NM | title = Is physician anesthesia cost-effective? | journal = Anesthesia and Analgesia | volume = 98 | issue = 3 | pages = 750–57, table of contents | date = March 2004 | pmid = 14980932 | doi = 10.1213/01.ANE.0000100945.56081.AC | s2cid = 7907307 }}</ref><ref name=When2007>{{cite journal | vauthors = Rosenbach ML, Cromwell J | title = When do anesthesiologists delegate? | journal = Medical Care | volume = 27 | issue = 5 | pages = 453–65 | date = May 1989 | pmid = 2725080 | doi = 10.1097/00005650-198905000-00002 | s2cid = 26298329 }}</ref> There can also be [[anesthesiologist assistant]]s (US) or [[physicians' assistant (anaesthesia)|physicians' assistants (anaesthesia)]] (UK) who assist with anesthesia.<ref name=Five>{{cite web|title=Five facts about AAs|publisher=American Academy of Anesthesiologist Assistants|archive-url=https://web.archive.org/web/20060926091707/http://www.anesthetist.org/content/view/14/38/|archive-date=2006-09-26|url=http://www.anesthetist.org/content/view/14/38/|access-date=2010-11-25}}</ref>

== Special populations ==
There are many circumstances when anesthesia needs to be altered for special circumstances due to the procedure (such as in [[cardiac surgery]], [[cardiothoracic anesthesiology]] or [[neurosurgery]]), the patient (such as in [[Pediatrics|pediatric anesthesia]], [[geriatric anesthesia|geriatric]], [[bariatric]] or [[Obstetrics|obstetrical anesthesia]]) or special circumstances (such as in [[Trauma (medicine)|trauma]], [[prehospital care]], [[robotic surgery]] or extreme environments).

== See also ==
{{Columns-list|colwidth=30em|
* [[Biomaterial]]
* [[Endoscopy]]
* [[Fluorescence image-guided surgery]]
* [[Hypnosurgery]]
* [[Jet ventilation]]
* [[List of surgical procedures]]
* [[Drain (surgery)|Surgical drain]]
* [[Wooden chest]] – a post opioid anesthesia condition
* [[Surgery]]
* [[Cardiac surgery]]
}}

== References ==
{{Reflist}}

== External links ==
* [http://guidance.nice.org.uk/CG3 NICE Guidelines on pre-operative tests]
* [https://web.archive.org/web/20140228165534/http://www.asahq.org/Home/For-Members/Clinical-Information/ASA-Physical-Status-Classification-System ASA Physical Status Classification]
* [https://web.archive.org/web/20140222041728/http://www.dmoz.org/search?q=anesthesia DMOZ link to anesthesia society sites]
* [https://grindgearzscience.com/a-comprehensive-guide-to-anesthetic-drugs-and-their-mechanisms-of-action/ A Comprehensive Guide to Anesthetic Drugs and Their Mechanisms of Action] {{Webarchive|url=https://web.archive.org/web/20230703051705/https://grindgearzscience.com/a-comprehensive-guide-to-anesthetic-drugs-and-their-mechanisms-of-action/ |date=3 July 2023 }}

{{Anesthesia}}
{{Medicine}}
{{Nursing}}
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[[Category:Anesthesia| ]]
[[Category:Anesthesiology]]
[[Category:Medical technology]]