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General anaesthesia

From Wikipedia, the free encyclopedia
General anaesthesia
Equipment used for anaesthesia in the operating room
SpecialtyAnaesthetics
UsesFacilitating surgery,terminal sedation[1]
ComplicationsAnaesthesia awareness,[2]overdose,[3]death[4]
MeSHD000768
MedlinePlus007410

General anaesthesia(UK) orgeneral anesthesia(US) is a method of medically inducing loss ofconsciousnessthat renders a patient unarousable even with painful stimuli.[5]This effect is achieved by administering either intravenous or inhalational general anaesthetic medications, which often act in combination with ananalgesicandneuromuscular blocking agent.Spontaneous ventilation is often inadequate during the procedure and intervention is often necessary to protect the airway.[5]General anaesthesia is generally performed in anoperating theaterto allow surgical procedures that would otherwise be intolerably painful for a patient, or in anintensive care unitoremergency departmentto facilitateendotracheal intubationand mechanical ventilation in critically ill patients. Depending on the procedure, general anaesthesia may be optional or required. Regardless of whether a patient may prefer to be unconscious or not, certainpain stimulicould result in involuntary responses from the patient (such as movement or muscle contractions) that may make an operation extremely difficult. Thus, for many procedures, general anaesthesia is required from a practical perspective.

A variety ofdrugsmay be administered, with the overall goal of achievingunconsciousness,amnesia,analgesia,loss of reflexes of theautonomic nervous system,and in some casesparalysisofskeletal muscles.The optimal combination of anesthetics for any given patient and procedure is typically selected by ananaesthetist,or another provider such as anurse anaesthetist(depending on local practice and law), in consultation with the patient and thesurgeon,dentist, or other practitioner performing the operative procedure.[6]

History

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Main article:History of general anesthesia
Further information:History of tracheal intubation

Attempts at producing a state of general anaesthesia can be traced throughout recorded history in the writings of the ancientSumerians,Babylonians,Assyrians,Egyptians,Greeks,Romans,Indians,andChinese.During theMiddle Ages,scientists and other scholars made significant advances in theEastern world,while their European counterparts also made important advances.

TheRenaissancesaw significant advances inanatomyandsurgical technique.However, despite all this progress, surgery remained a treatment of last resort. Largely because of the associatedpain,many patients chose certain death rather than undergo surgery. Although there has been a great deal of debate as to who deserves the most credit for the discovery of general anaesthesia, several scientific discoveries in the late 18th and early 19th centuries were critical to the eventual introduction and development of modern anaesthetic techniques.[7]

Two enormous leaps occurred in the late 19th century, which together allowed the transition to modern surgery. An appreciation of thegerm theory of diseaseled rapidly to the development and application ofantiseptictechniques in surgery. Antisepsis, which soon gave way toasepsis,reduced the overallmorbidityandmortalityof surgery to a far more acceptable rate than in previous eras.[8]Concurrent with these developments were the significant advances inpharmacologyandphysiologywhich led to the development of general anaesthesia and the control of pain. On 14 November 1804,Hanaoka Seishū,a Japanese surgeon, became the first person on record to successfully perform surgery using general anaesthesia.[9]

In the 20th century, the safety and efficacy of general anaesthesia was improved by the routine use oftracheal intubationand other advancedairway managementtechniques. Significant advances inmonitoringand newanaesthetic agentswith improvedpharmacokineticandpharmacodynamiccharacteristics also contributed to this trend. Finally, standardized training programs for anaesthesiologists andnurse anaesthetistsemerged during this period.

Purpose

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General anaesthesia has many purposes and is routinely used in almost all surgical procedures. An appropriate surgical anesthesia should include the following goals:

  1. Hypnosis/Unconsciousness (loss of awareness)
  2. Analgesia (loss of response to pain)
  3. Amnesia (loss of memory)
  4. Immobility (loss of motor reflexes)
  5. Paralysis (skeletal muscle relaxation and normal muscle relaxation)[3]

Instead of receiving continuous deep sedation, such as via benzodiazepines, dying patients may choose to be completely unconscious as they die.[1]

Biochemical mechanism of action

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Thebiochemicalmechanism of action of general anaestheticsis still controversial.[10]Theories need to explain the function of anaesthesia in animals and plants.[11]To induce unconsciousness, anaesthetics have myriad sites of action and affect thecentral nervous system(CNS) at multiple levels. General anaesthesia commonly interrupts or changes the functions of CNS components including thecerebral cortex,thalamus,reticular activating system,andspinal cord.Current theories on the anaesthetized state identify not only target sites in the CNS but alsoneural networksand arousal circuits linked with unconsciousness, and some anaesthetics potentially able to activate specific sleep-active regions.[12]

Two non-exclusionary mechanisms includemembrane-mediatedand directprotein-mediatedanesthesia. Potential protein-mediated molecular targets areGABAA,andNMDA glutamatereceptors. General anesthesia was hypothesized to either enhance the inhibitory transmission or reduce the excitatory transmission of neuro signaling.[13]Most volatile anesthetics have been found to be a GABAAagonist,although the site of action on the receptor remains unknown.[14]Ketamineis a non-competitiveNMDA receptor antagonist.[15]

The chemical structure and properties of anesthetics, as first noted byMeyer and Overton,suggest they could target the plasma membrane. Amembrane-mediatedmechanism that could account for the activation of an ion channel remained elusive until recently. A study from 2020 demonstrated that inhaled anesthetics (chloroformand isoflurane) could displacephospholipase D2from ordered lipid domains in the plasma membrane, which led to the production of the signaling moleculephosphatidic acid(PA). The signaling molecule activated TWIK-related K+ channels (TREK-1), a channel involved in anesthesia. PLDnullfruit flies were shown to resist anesthesia, the results established a membrane mediated target for inhaled anesthetics.[16]

Preoperative evaluation

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Prior to a planned procedure, the anesthesiologist reviews medical records, interviews the patient, and conducts a physical examination to obtain information regarding their medical history and current physical state, and to determine an appropriate anesthetic plan, including what combination of drugs and dosages will likely be needed for the patient's comfort and safety during the procedure. A variety of non-invasive and invasive monitoring devices may be necessary to ensure a safe and effective procedure. Key factors in this evaluation are the patient's age, gender,body mass index,medical and surgical history, current medications, exercise capacity, and fasting time.[17][18]Thorough and accurate preoperative evaluation is crucial for the effective safety of the anesthetic plan. For example, a patient who consumes significant quantities ofalcoholorillicit drugscould be undermedicated during the procedure if they fail to disclose this fact, and this could lead toanaesthesia awarenessor intraoperativehypertension.[2][19]Commonly used medications can also interact with anaesthetics, and failure to disclose such usage can increase the risk during the operation. Inaccurate timing of last meal can also increase the risk for aspiration of food, and lead to serious complications.[6]

An important aspect of pre-anaesthetic evaluation is an assessment of the patient'sairway,involving inspection of the mouth opening and visualisation of the soft tissues of thepharynx.[20]The condition of teeth and location ofdental crownsare checked, and neck flexibility and head extension are observed.[21][22]The most commonly performed airway assessment is the Mallampati classification, which evaluates the airway base on the ability to view airway structures with the mouth open and the tongue protruding. Mallampati tests alone have limited accuracy, and other evaluations are routinely performed addition to the Mallampati test including mouth opening, thyromental distance, neck range of motion, and mandibular protrusion. In a patient with suspected distorted airway anatomy, endoscopy or ultrasound is sometimes used to evaluate the airway before planning for the airway management.[23]

Premedication

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Prior to administration of a general anaesthetic, the anaesthetist may administer one or more drugs that complement or improve the quality or safety of the anaesthetic or simply provide anxiolysis. Premedication also often has mild sedative effects and may reduce the amount of anaesthetic agent required during the case.[6]

One commonly used premedication isclonidine,anAlpha -2 adrenergic agonist.[24][25]It reduces postoperative shivering,postoperative nausea and vomiting,and emergencedelirium.[6]However, a randomized controlled trial from 2021 demonstrated that clonidine is less effective at providing anxiolysis and more sedative in children of preschool age. Oral clonidine can take up to 45 minutes to take full effect,[26]The drawbacks of clonidine includehypotensionandbradycardia,but these can be advantageous in patients with hypertension and tachycardia.[27]Another commonly used Alpha -2 adrenergic agonist is dexmedetomidine, which is commonly used to provide a short term sedative effect (<24 hours).Dexmedetomidineand certainatypical antipsychoticagents may be also used in uncooperative children.[28]

Benzodiazepinesare the most commonly used class of drugs for premedication. The most commonly utilized benzodiazepine isMidazolam,which is characterized by a rapid onset and short duration. Midazolam is effective in reducingpreoperative anxiety,includingseparation anxietyin children.[29]It also provides mild sedation,sympathicolysis,andanterograde amnesia.[6]

Melatoninhas been found to be effective as an anaesthetic premedication in both adults and children because of itshypnotic,anxiolytic,sedative,analgesic,andanticonvulsantproperties. Recovery is more rapid after premedication with melatonin than with midazolam, and there is also a reduced incidence of post-operativeagitationand delirium.[30]Melatonin has been shown to have a similar effect in reducing perioperative anxiety in adult patients compared to benzodiazepine.[31]

Another example of anaesthetic premedication is the preoperative administration ofbeta adrenergic antagonists,which reduce the burden of arrhythmias after cardiac surgery. However, evidence also has shown an association of increased adverse events with beta-blockers in non-cardiac surgery.[32]Anaesthesiologists may administer one or moreantiemeticagents such asondansetron,droperidol,ordexamethasoneto prevent postoperative nausea and vomiting.[6]NSAIDs are commonly used analgesic premedication agent, and often reduce need foropioidssuch asfentanylorsufentanil.Alsogastrokineticagents such asmetoclopramide,andhistamine antagonistssuch asfamotidine.[6]

Non-pharmacologic preanaesthetic interventions include playingcognitive behavioral therapy,music therapy, aromatherapy, hypnosismassage,pre-operative preparation video, and guided imagery relaxation therapy, etc.[33]These techniques are particularly useful for children and patients withintellectual disabilities.Minimizing sensory stimulation or distraction by video games may help to reduce anxiety prior to or during induction of general anaesthesia. Larger high-quality studies are needed to confirm the most effective non-pharmacological approaches for reducing this type of anxiety.[34]Parental presence during premedication and induction of anaesthesia has not been shown to reduce anxiety in children.[34]It is suggested that parents who wish to attend should not be actively discouraged, and parents who prefer not to be present should not be actively encouraged to attend.[34]

Anesthesia and the brain

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Anesthesia has little to no effect on brain function, unless there is an existing brain disruption. Barbiturates, or the drugs used to administer anesthesia do not affect auditory brain stem response.[35]An example of a brain disruption would be a concussion.[36]It can be risky and lead to further brain injury if anesthesia is used on a concussed person. Concussions create ionic shifts in the brain that adjust the neuronal transmembrane potential. In order to restore this potential more glucose has to be made to equal the potential that is lost. This can be very dangerous and lead to cell death. This makes the brain very vulnerable in surgery. There are also changes to cerebral blood flow. The injury complicates the oxygen blood flow and supply to the brain.

Stages of anaesthesia

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Guedel's classification,described byArthur Ernest Guedelin 1937,[3]describes four stages of anaesthesia. Despite newer anaesthetic agents and delivery techniques, which have led to more rapid onset of—and recovery from—anaesthesia (in some cases bypassing some of the stages entirely), the principles remain.

Stage 1
Stage 1, also known asinduction,is the period between the administration of induction agents and loss of consciousness. During this stage, the patient progresses from analgesia without amnesia to analgesia with amnesia. Patients can carry on a conversation at this time, and may complain about visual disturbance.
Stage 2
Stage 2, also known as theexcitement or delirium stage,is the period following loss of consciousness and marked by excited and delirious activity. During this stage, the patient'srespirationandheart ratemay become irregular. In addition, there may be uncontrolled movements, vomiting,suspension of breathing,andpupillary dilation.Because the combination of spastic movements, vomiting, and irregular respiration may compromise the patient's airway, rapidly acting drugs are used to minimize time in this stage and reach Stage 3 as fast as possible.

Stage 3
In Stage 3, also known assurgical anaesthesia,the skeletal muscles relax, vomiting stops. Respiratory depression and cessation of eye movements are the hallmarks of this stage. The patient is unconscious and ready for surgery. This stage is divided into four planes:
  1. The eyes roll, then become fixed; eyelid and swallow reflexes are lost. Still have regular spontaneous breathing;
  2. Corneal and laryngeal reflexes are lost;
  3. The pupillary light reflex is lost; and the process is marked by complete relaxation of abdominal and intercostal muscles. Ideal level of anesthesia for most surgeries.
  4. Full diaphragm paralysis and irregular shallow abdominal respiration occur.[37]
Stage 4
Stage 4, also known asoverdose,occurs when too much anaesthetic medication is given relative to the amount of surgical stimulation and the patient has severebrainstemormedullarydepression, resulting in a cessation of respiration and potential cardiovascular collapse. This stage is lethal without cardiovascular and respiratory support.[3]

Induction

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General anaesthesia is usually induced in anoperating theatreor in a dedicated anaesthetic room adjacent to the theatre. General anaesthesia may also be conducted in other locations, such as anendoscopysuite,intensive care unit,radiologyorcardiologydepartment,emergency department,ambulance, or at the site of adisasterwhere extrication of the patient may be impossible or impractical.

Anaesthetic agents may be administered by various routes, includinginhalation,injection(intravenous,intramuscular,orsubcutaneous),oral,andrectal.Once they enter thecirculatory system,the agents are transported to their biochemicalsites of actionin thecentralandautonomicnervous systems.

Most general anaesthetics are induced either intravenously or by inhalation. Commonly used intravenous induction agents includepropofol,sodium thiopental,etomidate,methohexital,andketamine.Inhalational anaesthesiamay be chosen when intravenous access is difficult to obtain (e.g., children), when difficulty maintaining the airway is anticipated, or when the patient prefers it.Sevofluraneis the most commonly used agent for inhalational induction, because it is less irritating to thetracheobronchial treethan other agents.[38]

As an example sequence of induction drugs:

  1. Pre-oxygenation or denitrogenation to fill lungs with 100% oxygen to permit a longer period of apnea during intubation without affecting blood oxygen levels
  2. Fentanylfor systemic analgesia during intubation
  3. Propofolfor sedation for intubation
  4. Switching from oxygen to a mixture of oxygen andinhalational anestheticonce intubation is complete

Laryngoscopyand intubation are both very stimulating. The process of induction blunts the response to these maneuvers while simultaneously inducing a near-coma state to prevent awareness.

Physiologic monitoring

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Severalmonitoringtechnologies allow for a controlled induction of, maintenance of, and emergence from general anaesthesia. Standard for basic anesthetic monitoring is a guideline published by the ASA, which describes that the patient's oxygenation, ventilation, circulation and temperature should be continually evaluated during anesthetic.[39]

  1. Continuouselectrocardiography(ECG or EKG):Electrodesare placed on the patient's skin to monitor heart rate and rhythm. This may also help the anaesthesiologist to identify early signs of heartischaemia.Typically lead II and V5 are monitored for arrhythmias and ischemia, respectively.
  2. Continuouspulse oximetry(SpO2): A device is placed, usually on a finger, to allow for early detection of a fall in a patient'shemoglobinsaturation with oxygen (hypoxaemia).
  3. Blood pressure monitoring:There are two methods of measuring the patient's blood pressure. The first, and most common, is non-invasive blood pressure (NIBP) monitoring. This involves placing ablood pressure cuffaround the patient's arm, forearm, or leg. A machine takes blood pressure readings at regular, preset intervals throughout the surgery. The second method is invasive blood pressure (IBP) monitoring, which allows beat to beat monitoring of blood pressure. This method is reserved for patients with significant heart or lung disease, the critically ill, and those undergoing major procedures such as cardiac or transplant surgery, or when large blood loss is expected. It involves placing a special type of plasticcannulain an artery, usually in the wrist (radial artery) or groin (femoral artery).
  4. Agent concentration measurement:anaesthetic machinestypically have monitors to measure the percentage of inhalational anaesthetic agents used as well as exhalation concentrations. These monitors include measuringoxygen,carbon dioxide,andinhalational anaesthetics(e.g.,nitrous oxide,isoflurane).
  5. Oxygen measurement:Almost all circuits have an alarm in case oxygen delivery to the patient is compromised. The alarm goes off if the fraction of inspired oxygen drops below a set threshold.
  6. Acircuit disconnect alarmorlow pressure alarmindicates failure of the circuit to achieve a given pressure duringmechanical ventilation.
  7. Capnographymeasures the amount ofcarbon dioxideexhaled by the patient in percent or mmHg, allowing the anaesthesiologist to assess the adequacy ofventilation.MmHg is usually used to allow the provider to see more subtle changes.
  8. Temperature measurementto discernhypothermiaor fever, and to allow early detection ofmalignant hyperthermia.
  9. Electroencephalography,entropy monitoring,or other systems may be used to verify the depth of anaesthesia. This reduces the likelihood ofanaesthesia awarenessand of overdose.

Airway management

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Main article:Airway management

Anaesthetized patients lose protective airway reflexes (such as coughing),airway patency,and sometimes a regular breathing pattern due to the effects of anaesthetics,opioids,ormuscle relaxants. To maintain an open airway and regulate breathing, some form ofbreathing tubeis inserted after the patient is unconscious. To enablemechanical ventilation,anendotracheal tubeis often used, although there are alternative devices that can assist respiration, such as face masks orlaryngeal mask airways. Generally, full mechanical ventilation is only used if a very deep state of general anaesthesia is to be induced for a major procedure, and/or with a profoundly ill or injured patient. That said, induction of general anaesthesia usually results inapneaand requires ventilation until the drugs wear off and spontaneous breathing starts. In other words, ventilation may be required for both induction and maintenance of general anaesthesia or just during the induction. However, mechanical ventilation can provide ventilatory support during spontaneous breathing to ensure adequate gas exchange.

General anaesthesia can also be induced with the patient spontaneously breathing and therefore maintaining their own oxygenation which can be beneficial in certain scenarios (e.g. difficult airway or tubeless surgery). Spontaneous ventilation has been traditionally maintained with inhalational agents (i.e. halothane or sevoflurane) which is called a gas or inhalational induction. Spontaneous ventilation can also be maintained using intravenous anaesthesia (e.g. propofol). Intravenous anaesthesia to maintain spontaneous respiration has certain advantages over inhalational agents (i.e. suppressed laryngeal reflexes) however it requires careful titration. Spontaneous Respiration using Intravenous anaesthesia and High-flow nasal oxygen (STRIVE Hi) is a technique that has been used in difficult and obstructed airways.[40]

Eye management

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Main article:Eye injuries during general anaesthesia

General anaesthesia reduces thetonic contractionof theorbicularis oculi muscle,causinglagophthalmos(incomplete eye closure) in 59% of people.[41]In addition, tear production and tear-film stability are reduced, resulting in corneal epithelial drying and reducedlysosomalprotection. The protection afforded byBell's phenomenon(in which the eyeball turns upward during sleep, protecting the cornea) is also lost. Careful management is required to reduce the likelihood ofeye injuries during general anaesthesia.[42]Some of the methods to prevent eye injury during general anesthesia includes taping the eyelids shut, use of eye ointments, and specially designed eye protective goggles.

Neuromuscular blockade

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Syringesprepared with medications that are expected to be used during an operation under general anaesthesia maintained bysevofluranegas:
-Propofol,a hypnotic
-Ephedrine,in case ofhypotension
-Fentanyl,foranalgesia
-Atracurium,forneuromuscular block
-Glycopyrronium bromide(here under trade name Robinul), reducing secretions

Paralysis, or temporary muscle relaxation with aneuromuscular blocker,is an integral part of modern anaesthesia. The first drug used for this purpose wascurare,introduced in the 1940s, which has now been superseded by drugs with fewer side effects and, generally, shorter duration of action.[43]Muscle relaxation allows surgery within majorbody cavities,such as theabdomenandthorax,without the need for very deep anaesthesia, and also facilitatesendotracheal intubation.

Acetylcholine,a naturalneurotransmitterfound at theneuromuscular junction,causes muscles to contract when it is released from nerve endings. Muscle paralytic drugs work by preventing acetylcholine from attaching to its receptor. Paralysis of the muscles of respiration—thediaphragmandintercostal musclesof the chest—requires that some form of artificial respiration be implemented. Because the muscles of thelarynxare also paralysed, the airway usually needs to be protected by means of anendotracheal tube.[6]

Paralysis is most easily monitored by means of a peripheral nerve stimulator. This device intermittently sends short electrical pulses through the skin over a peripheral nerve while the contraction of a muscle supplied by that nerve is observed. The effects of muscle relaxants are commonly reversed at the end of surgery byanticholinesterasedrugs, which are administered in combination with muscarinicanticholinergicdrugs to minimize side effects. Examples of skeletal muscle relaxants in use today arepancuronium,rocuronium,vecuronium,cisatracurium,atracurium,mivacurium,andsuccinylcholine.Novel neuromuscular blockade reversal agents such assugammadexmay also be used; it works by directly binding muscle relaxants and removing it from the neuromuscular junction. Sugammadex was approved for use in the United States in 2015, and rapidly gained popularity. A study from 2022 has shown that Sugammadex and neostigmine are likely similarly safe in the reversal of neuromuscular blockade.[44]

Maintenance

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The duration of action of intravenous induction agents is generally 5 to 10 minutes, after which spontaneous recovery of consciousness will occur.[45]In order to prolong unconsciousness for the duration of surgery, anaesthesia must be maintained. This is achieved by allowing the patient to breathe a carefully controlled mixture of oxygen and avolatile anaestheticagent, or by administering intravenous medication (usuallypropofol). Inhaled anaesthetic agents are also frequently supplemented by intravenous analgesic agents, such asopioids(usuallyfentanylor a fentanyl derivative) andsedatives(usually propofol or midazolam). Propofol can be used for total intravenous anaesthetia (TIVA), therefore supplementation by inhalation agents is not required.[46]General anesthesia is usually considered safe; however, there are reported cases of patients with distortion of taste and/or smell due to local anesthetics, stroke, nerve damage, or as a side effect of general anesthesia.[47][48]

At the end of surgery, administration of anaesthetic agents is discontinued. Recovery of consciousness occurs when the concentration of anaesthetic in the brain drops below a certain level (this occurs usually within 1 to 30 minutes, mostly depending on the duration of surgery).[6]

In the 1990s, a novel method of maintaining anaesthesia was developed inGlasgow,Scotland. Calledtarget controlled infusion(TCI), it involves using a computer-controlled syringe driver (pump) to infuse propofol throughout the duration of surgery, removing the need for a volatile anaesthetic and allowing pharmacologic principles to more precisely guide the amount of the drug used by setting the desired drug concentration. Advantages include faster recovery from anaesthesia, reduced incidence of postoperative nausea and vomiting, and absence of a trigger formalignant hyperthermia.At present, TCI is not permitted in the United States, but a syringe pump delivering a specific rate of medication is commonly used instead.[49]

Other medications are occasionally used to treat side effects or prevent complications. They includeantihypertensivesto treat high blood pressure;ephedrineorphenylephrineto treat low blood pressure;salbutamolto treatasthma,laryngospasm,orbronchospasm;andepinephrineordiphenhydramineto treat allergic reactions.Glucocorticoidsorantibioticsare sometimes given to prevent inflammation and infection, respectively.[6]

Emergence

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Emergence is the return to baseline physiologic function of all organ systems after the cessation of general anaesthetics. This stage may be accompanied by temporary neurologic phenomena, such asagitated emergence(acute mental confusion),aphasia(impaired production or comprehension of speech), or focal impairment in sensory or motor function.Shiveringis also fairly common and can be clinically significant because it causes an increase inoxygenconsumption,carbon dioxideproduction,cardiac output,heart rate,andsystemic blood pressure.The proposed mechanism is based on the observation that the spinal cord recovers at a faster rate than the brain. This results in uninhibited spinal reflexes manifested asclonicactivity (shivering). This theory is supported by the fact thatdoxapram,aCNSstimulant, is somewhat effective in abolishing postoperative shivering.[50]Cardiovascular events such as increased or decreased blood pressure,rapid heart rate,or othercardiac dysrhythmiasare also common during emergence from general anaesthesia, as are respiratory symptoms such asdyspnoea.Responding and following verbal command, is a criterion commonly utilized to assess the patient's readiness for tracheal extubation.[6]

Postoperative care

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Anaesthetized patient in postoperative recovery.

Postoperative pain is managed in theanaesthesia recovery unit(PACU) withregional analgesiaor oral,transdermal,orparenteralmedication. Patients may be givenopioids,as well as other medications likenon steroidal anti-inflammatory drugsandacetaminophen.[51]Sometimes, opioid medication is administered by the patient themselves using a system called apatient controlled analgesic.[52]The patient presses a button to activate a syringe device and receive a preset dose or "bolus" of the drug, usually a strong opioid such asmorphine,fentanyl,oroxycodone(e.g., one milligram of morphine). The PCA device then "locks out" for a preset period to allow the drug to take effect, and also prevent the patient from overdosing. If the patient becomes too sleepy or sedated, they make no more requests. This confers a fail-safe aspect that is lacking in continuous-infusion techniques. If these medications cannot effectively manage the pain, local anesthetic may be directly injected to the nerve in a procedure called anerve block.[53][54]

In the recovery unit, many vital signs are monitored, includingoxygen saturation,[55][56]heart rhythm and respiration,[55][57]blood pressure,[55]andcore body temperature.

Postanesthetic shiveringis common. Apart from causing discomfort and exacerbating pain, shivering has been shown to increase oxygen consumption,catecholaminerelease, risk for hypothermia, and induce lactic acidosis.[58]A number of techniques are used to reduce shivering, such as warm blankets,[59][60]or wrapping the patient in a sheet that circulates warmed air, called abair hugger.[61][62]If the shivering cannot be managed with external warming devices, drugs such asdexmedetomidine,[63][64]or other α2-agonists, anticholinergics, central nervous system stimulants, or corticosteroids may be used.[51][65]

In many cases, opioids used in general anaesthesia can cause postoperativeileus,even after non-abdominal surgery. Administration of aμ-opioidantagonistsuch asalvimopanimmediately after surgery can help accelerate the timing of hospital discharge, but does not reduce the development of paralytic ileus.[66]

Enhanced Recovery After Surgery (ERAS) is a society that provides up-to-date guidelines and consensus to ensure continuity of care and improve recovery and peri-operative care. Adherence to the pathway and guidelines has been shown to associate with improved post-operative outcomes and lower costs to the health care system.[67]

Perioperative mortality

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Main article:Perioperative mortality

Mostperioperative mortalityis attributable tocomplicationsfrom the operation, such ashaemorrhage,sepsis,and failure of vital organs. Over the last several decades, the overall anesthesia related mortality rate improved significantly for anesthetics administered. Advancements in monitoring equipment, anesthetic agents, and increased focus on perioperative safety are some reasons for the decrease in perioperative mortality. In the United States, the current estimated anesthesia-related mortality is about 1.1 per million population per year. The highest death rates were found in the geriatric population, especially those 85 and older.[68]A review from 2018 examined perioperative anesthesia interventions and their impact on anesthesia-related mortality. Interventions found to reduce mortality include pharmacotherapy, ventilation, transfusion, nutrition, glucose control, dialysis and medical device.[69]Interestingly, a randomized controlled trial from 2022 demonstrated that there is no significant difference in mortality between patient receiving handover from one clinician to another compared to the control group.[70]

Mortality directly related to anaesthetic management is very uncommon but may be caused bypulmonary aspirationof gastric contents,[71]asphyxiation,[72]oranaphylaxis.[4]These in turn may result from malfunction ofanaesthesia-related equipmentor, more commonly,human error.In 1984, after a television programme highlighting anaesthesia mishaps aired in the United States, American anaesthesiologistEllison C. Pierceappointed the Anesthesia Patient Safety and Risk Management Committee within theAmerican Society of Anesthesiologists.[73]This committee was tasked with determining and reducing the causes of anaesthesia-relatedmorbidityand mortality.[73]An outgrowth of this committee, the Anesthesia Patient Safety Foundation, was created in 1985 as an independent, nonprofit corporation with the goal "that no patient shall be harmed by anesthesia".[74]

The rare but major complication of general anaesthesia is malignant hyperthermia.[75][76]All major hospitals should have a protocol in place with an emergence drug cart near the OR for this potential complication.[77]

See also

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References

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