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Anesthesia

Anesthesia or anaesthesia 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, paralysis, amnesia, and unconsciousness. An individual under the effects of anesthetic drugs is referred to as being anesthetized.

Medical uses
The purpose of anesthesia can be distilled down to three basic goals or endpoints: • 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 reflexes) • 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 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. To achieve the goals of anesthesia, drugs act on different but interconnected parts of the nervous system. Hypnosis, for instance, is generated through actions on the nuclei in the brain and is similar to the activation of sleep. The effect is to make people less aware and less reactive to noxious stimuli. Loss of memory (amnesia) is created by action of drugs on multiple (but specific) regions of the brain. Memories are created as either declarative or non-declarative memories in several stages (short-term, long-term, long-lasting) the strength of which is determined by the strength of connections between neurons termed synaptic plasticity. 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. Nevertheless, a person can 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". It is not known whether animals dream while under general anesthesia. == Techniques ==
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 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. 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. 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. The more detailed pre-operative medical history aims to discover genetic disorders (such as malignant hyperthermia or pseudocholinesterase deficiency), habits (tobacco, drug and alcohol use), physical attributes (such as obesity or a difficult airway) and any coexisting diseases (especially cardiac and respiratory diseases) that might impact the anesthetic. The preanesthetic physical examination helps quantify the impact of anything found in the medical history in addition to lab tests. Intravenous anesthetic is delivered either by bolus doses or an infusion pump. There are also many smaller instruments used in airway management and monitoring the patient. The common thread to modern machinery in this field is the use of fail-safe systems that decrease the odds of catastrophic misuse of the machine. Monitoring with integrated systems for monitoring of several vital parameters Patients under general anesthesia must undergo continuous physiological 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. 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 artery occlusion pressure, cardiac output, 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. Sedation Sedation (also referred to as dissociative anesthesia or twilight anesthesia) creates hypnotic, 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 benzodiazepines are usually given with pain relievers (such as narcotics, or local anesthetics or both) because they do not, by themselves, provide significant pain relief. 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 benzodiazepines, 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.). • 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 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. EMLA patches). • Tumescent anesthesia: a large amount of very dilute local anesthetics are injected into the subcutaneous tissues 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. Low quality evidence was found 3 to 12 months following breast cancer surgery. 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. Nerve blocks are also associated with a lower risk of neurologic complications compared to the more central epidural or spinal neuraxial blocks. or ketamine. 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. Common preemptive approaches include epidural neuraxial blockade or nerve blocks. == Risks and complications ==
Risks and complications
Risks and complications as they relate to anesthesia are classified as either morbidity (a disease or disorder that results from anesthesia) or 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. Morbidity can be major (myocardial infarction, pneumonia, pulmonary embolism, kidney failure/chronic kidney disease, postoperative cognitive dysfunction and 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. but to what degree is uncertain. 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). 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." 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). == Recovery ==
Recovery
The immediate time after anesthesia is called emergence. Emergence from general anesthesia or sedation requires careful monitoring because there is still a risk of complication. Nausea and vomiting are reported at 9.8% but will vary with the type of anesthetic and procedure. There is a need for 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. 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. 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." 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. There is good evidence that POCD occurs after cardiac surgery and the major reason for its occurrence is the formation of 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. == History ==
History
The first attempts at general anesthesia were probably herbal remedies administered in prehistory. Alcohol is one of the oldest known sedatives and it was used in ancient Mesopotamia thousands of years ago. The Sumerians are said to have cultivated and harvested the opium poppy (Papaver somniferum) in lower Mesopotamia as early as 3400 BCE. The ancient Egyptians had some surgical instruments, as well as crude analgesics and sedatives, including possibly an extract prepared from the mandrake fruit. In China, Bian Que (Chinese: 扁鹊, Wade–Giles: ''Pien Ch'iao'', ) was a legendary Chinese internist and surgeon who reportedly used general anesthesia for surgical procedures. 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. Throughout Europe, Asia, and the Americas, a variety of Solanum species containing potent tropane alkaloids 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 shamans chewed coca leaves and performed operations on the skull while spitting into the wounds they had inflicted to anesthetize. Cocaine was later isolated and became the first effective local anesthetic. It was first used in eye surgery in 1884 by Karl Koller, at the suggestion of Sigmund Freud. German surgeon August Bier (1861–1949) was the first to use cocaine for intrathecal anesthesia in 1898. Romanian surgeon Nicolae Racoviceanu-Piteşti (1860–1942) was the first to use opioids for intrathecal analgesia; he presented his experience in Paris in 1901. The "soporific sponge" ("sleep sponge") used by Arabic physicians was introduced to Europe by the 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, 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. '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, ether, may have been synthesized as early as the 8th century, 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. 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 oxides. 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". 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. Hanaoka learned traditional Japanese medicine as well as 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 Korean morning glory and other herbs. 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 malignant tumors, extraction of bladder stones, and extremity amputations. 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 national isolation policy of the Tokugawa shogunate prevented Hanaoka's achievements from being publicized until after the isolation ended. Nearly forty years would pass before Crawford Long, who is titled as the inventor of modern anesthetics in the West, used general anesthesia in Jefferson, Georgia. 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. operation conducted at Massachusetts General Hospital. The daguerreotype was taken by Southworth & Hawes on July 3, 1847. 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. On 16 October 1846, Boston dentist William Thomas Green Morton gave a successful demonstration using diethyl ether to medical students at the same venue. 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 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". 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. 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. 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. 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. Chloroform gained royal approval in 1853 when John Snow administered it to Queen Victoria when she was in labor with Prince Leopold. For the experience of child birth itself, chloroform met all the Queen's expectations; she stated it was "delightful beyond measure". 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. 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" These qualities of an anesthetist were often found in submissive medical students and even members of the public. More often, surgeons sought out nurses to provide anesthesia. By the time of the 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. Snow also involved himself in the production of equipment needed for the administration of inhalational anesthetics, the forerunner of today's anesthesia machines. 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. 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. 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. == Society and culture ==
Society and culture
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. 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. 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. There can also be anesthesiologist assistants (US) or physicians' assistants (anaesthesia) (UK) who assist with anesthesia. == Special populations ==
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 pediatric anesthesia, geriatric, bariatric or obstetrical anesthesia) or special circumstances (such as in trauma, prehospital care, robotic surgery or extreme environments). == See also ==
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