Editing Anesthesia (section)

=== Regional anesthesia ===
{{Further|Conduction anesthesia}}
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| caption1  = Sonography guided femoral nerve block

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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}}