Editing Anesthesia (section)

== Techniques ==
Anesthesia is unique in that it is not a direct means of treatment; rather, it allows the clinician to do things that may treat, diagnose, or cure an ailment which would otherwise be painful or complicated. The best anesthetic, therefore, is the one with the lowest risk to the patient that still achieves the endpoints required to complete the procedure. The first stage in anesthesia is the 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>[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>

=== 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=":0">{{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|pages=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=":0" />  This review acknowledges certain limitations that impact its applicability beyond the surgeries and regional anesthesia techniques reviewed.<ref name=":0" />

==== 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 |pages=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 | pages = 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 | pages = CD009351 | date = September 2012 | pmid = 22972140 | doi = 10.1002/14651858.CD009351.pub2 | hdl-access = free | hdl = 1871/48559 }}</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 | pages = 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 | pages = 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 | pages = 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 | pages = CD005059 | date = January 2016 | volume = 2017 | pmid = 26731032 | pmc = 6464571 | doi = 10.1002/14651858.CD005059.pub4 }}</ref>