Not to be confused with Paresthesia.
For other uses, see Anesthesia (disambiguation).

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Anesthesia, or anaesthesia (from Greek αν-, an-, "without"; and αἴσθησις, aisthēsis, "sensation"),[1] traditionally meant the condition of having sensation (including the feeling of pain) blocked or temporarily taken away. It is a pharmacologically induced and reversible state of amnesia, analgesia, loss of responsiveness, loss of skeletal muscle reflexes, decreased stress response, or all of these simultaneously. These effects can be obtained from a single drug which alone provides the correct combination of effects, or occasionally a combination of drugs (such as hypnotics, sedatives, paralytics and analgesics) to achieve very specific combinations of results. This allows patients to undergo surgery and other procedures without the distress and pain they would otherwise experience. An alternative definition is a "reversible lack of awareness," including a total lack of awareness (e.g. a general anesthetic) or a lack of awareness of a part of the body such as a spinal anesthetic. The pre-existing word anesthesia was suggested by Oliver Wendell Holmes, Sr. in 1846 as a word to use to describe this state.[2]

Types of anesthesia include local anesthesia, regional anesthesia, general anesthesia, and dissociative anesthesia. Local anesthesia inhibits sensory perception within a specific location on the body, such as a tooth or the urinary bladder. Regional anesthesia renders a larger area of the body insensate by blocking transmission of nerve impulses between a part of the body and the spinal cord. Two frequently used types of regional anesthesia are spinal anesthesia and epidural anesthesia. General anesthesia refers to inhibition of sensory, motor and sympathetic nerve transmission at the level of the brain, resulting in unconsciousness and lack of sensation. Dissociative anesthesia uses agents that inhibit transmission of nerve impulses between higher centers of the brain (such as the cerebral cortex) and the lower centers, such as those found within the limbic system.



Doctors specializing in 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.[3] 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 anesthesiologist assistants or certified registered nurse anesthetists (CRNAs), and about 10% are provided by CRNAs in solo practice.[4][5][3]


Main article: Anesthesiologist

In the strict sense, the term anesthetist refers to any individual who administers anesthesia. In the US, however, the term is most commonly employed to refer to registered nurses who have completed specialized education and training in anesthesia to become certified registered nurse anesthetists (CRNAs). In the US and Canada, medical physicians who specialize in anesthesiology are called anesthesiologists. Such physicians in the United Kingdom (UK), Australia and New Zealand are called anaesthetists.

In the US, a physician specializing in anesthesiology typically completes four years of college, four years of medical school, and four years of postgraduate medical training or residency[6] According to the American Society of Anesthesiologists, anesthesiologists provide or participate in more than ninety percent of the forty million anesthetics delivered annually.[7] In the UK, this training lasts a minimum of seven years after the awarding of a medical degree and two years of basic residency, and takes place under the supervision of the Royal College of Anaesthetists. In Australia and New Zealand, it lasts five years after the awarding of a medical degree and two years of basic residency, under the supervision of the Australian and New Zealand College of Anaesthetists.[8] Other countries have similar systems, including Ireland (the Faculty of Anaesthetists of the Royal College of Surgeons in Ireland), Canada and South Africa (the College of Anaesthetists of South Africa).

In the US, satisfactory completion of the written and oral Board examinations allows an anesthesiologist to be called a "Diplomate" of the American Board of Anesthesiology or of the American Osteopathic Board of Anesthesiology. This is often referred to colloquially as being "Board Certified". In the UK, Fellowship of the Royal College of Anaesthetists (FRCA) is conferred upon medical doctors following satisfactory completion of the written and oral parts of the Royal College's examination.

The role of the anesthesiologist is no longer limited to the operation itself. Many anesthesiologists function as perioperative physicians, ensuring optimal analgesia and maintenance of physiologic homeostasis throughout the preoperative, intraoperative, and postoperative periods. Anesthesiologists may elect to subspecialize in anesthesia for particular types of surgery (cardiothoracic, obstetrical, neurosurgical, pediatric), regional anesthesia, acute or chronic pain medicine, or Intensive Care Medicine.

Anesthesia providers are often trained using full scale human simulators. The field was an early adopter of this technology and has used it to train students and practitioners at all levels for the past several decades. Notable centers in the United States can be found at the Johns Hopkins Medicine Simulation Center,[9] Harvard's Center for Medical Simulation,[10] Stanford,[11] The Mount Sinai School of Medicine HELPS Center in New York,[12] Duke University,[13]and the University of Utah. [14]

Nurse anesthetists

Main article: Nurse anesthetist

In the United States, advanced practice nurses specializing in the provision of anesthesia care are known as certified registered nurse anesthetists (CRNAs). According to the American Association of Nurse Anesthetists, the 39,000 CRNAs in the US administer approximately 30 million anesthetics each year, roughly two thirds of the US total. 34% of nurse anesthetists practice in communities of less than 50,000. CRNAs start school with a bachelors degree in nursing and at least 1 year of acute care nursing experience, and gain a masters degree in nurse anesthesia before passing the mandatory Certification Exam. Masters-level CRNA training programs range in length from 24 to 36 months.

CRNAs may work with podiatrists, dentists, anesthesiologists, surgeons, obstetricians and other professionals requiring their services. CRNAs administer anesthesia in all types of surgical cases, and are able to apply all the accepted anesthetic techniques—general, regional, local, or sedation. 34 states require physician supervision of a CRNA's practice, and hospitals can regulate what CRNAs can or can not do based on local laws.

In the United States, the Centers for Medicare and Medicaid Services (CMS), a federal agency within the United States Department of Health and Human Services, determines the conditions for payment for all anesthesia services provided under the Medicare, Medicaid, and State Children's Health Insurance Program (SCHIP) programs. For the purposes of payment for anesthesiology services, CMS defines an anesthesia practitioner as a physician who performs the anesthesia service alone, a CRNA who is not medically directed, or a CRNA or AA who is medically directed.[15] Under the QZ Anesthesia Claims Modifier, CMS allows payment to a CRNA for anesthesiology services provided under these programs without medical direction by a physician.[15] Furthermore, under CMS regulations, anesthesia must be administered only by:

The aforementioned exemption for CRNAs is the State exemption (also referred to as an "opt-out"). Under the State exemption, if the State in which the hospital is located submits a letter to CMS requesting exemption from physician supervision of CRNAs, and that letter has been signed by the Governor of that State, then hospitals within that State may be exempted from the requirement for physician supervision of CRNAs.[16] In 2001, CMS established this exemption for CRNAs from the physician supervision requirement by recognizing a Governor's written request to CMS attesting that it is in the best interests of the State's citizens to exercise this exemption.[17] As of September 2010, sixteen states (California, Iowa, Nebraska, Idaho, Minnesota, New Hampshire, New Mexico, Kansas, North Dakota, Washington, Alaska, Oregon, South Dakota, Wisconsin, Montana and Colorado) have chosen to opt-out of the CRNA physician supervision regulation.[17]

Anesthesiologist assistants

Main article: Anesthesiologist assistant

In the United States, anesthesiologist assistants (AAs) are graduate-level trained specialists who have undertaken specialized education and training to provide anesthesia care under the direction of an anesthesiologist. AAs typically hold a masters degree and practice under anesthesiologist supervision in 18 states and the District of Columbia through licensing, certification or physician delegation.[18]

In the UK, a similar group of assistants are currently being evaluated. They are referred to as "physician assistant (anaesthesia)" (PAA). Their background can be nursing, operating department practice, another of the allied medical professions, or even one of the natural sciences.[19] Training is in the form of a postgraduate diploma and takes 27 months to complete.[19]

Operating department practitioners

In the United Kingdom, operating department practitioners provide assistance and support to the anesthetist or anesthesiologist. They can also assist the surgeon with surgical procedures and provide postoperative care to patients emerging from anesthesia. ODPs can be found in the operating department, accident and emergency department, intensive care unit, high dependency unit and in radiology, cardiology and endoscopy suites which require anesthesia support. They may also work with organ transplantation teams, as well as provide pre-hospital care to trauma victims. They are state-registered in the UK. The ODP is a mid-level practitioner of perioperative medicine. ODPs also function as lecturers and trainers in cardiopulmonary resuscitation, and work in management positions in operating departments.

Veterinary anesthetists

Main article: Veterinary anesthesia

Much of the equipment and drugs utilized by veterinary anesthetists is similar or identical to that used in anesthesia for human patients. There are vast differences in the physiology of different animal species, which may influence the choice of anesthetic agents and delivery systems in organisms ranging in diversity from (for example) annelids to elephants. For many wild animals, anesthetic drugs must often be delivered from a distance by means of remote projector systems ("dart guns") before the animal can even be approached. Large domestic livestock can often be anesthetized for certain types of surgery in the standing position using only local anesthetics and sedative drugs. While most clinical veterinarians and veterinary technicians routinely function as anesthetists in the course of their professional duties, veterinary anesthesiologists in the U.S. are veterinarians who have completed a three year residency in anesthesia and have qualified for certification by the American College of Veterinary Anesthesiologists.

Other personnel

Anesthesia technicians are specially trained Anaesthetic Assistants,equivalent to Operating Department Practitioners in Great Britain. They do not administer anesthesia, but rather they assist anesthesia providers similar to the way in which scrub technicians assist surgeons. Commonly these services are collectively called perioperative services, and thus the term perioperative service technician (PST) is used interchangeably with anesthesia technician. In the United States, an anesthesia technician can become a Certified Anesthesia Technician (Cer.A.T.), followed by becoming a Certified Anesthesia Technologist (Cer.A.T.T.) through American Society of Anesthesia Technologists & Technicians (ASATT).[20] In New Zealand, an anesthetic technician completes a course of study recognized by the New Zealand Anaesthetic Technicians Society.[21]


Further information: Anesthetic, General anesthetic, Inhalational anesthetic and Local anesthetic

An anesthetic agent is a drug that brings about a state of anesthesia. A wide variety of drugs are used in modern anesthetic practice. Many are rarely used outside of anesthesia, although others are used commonly by all disciplines. Anesthetics are categorized into two categories: general anesthetics cause a reversible loss of consciousness (general anesthesia), while local anesthetics cause reversible local anesthesia and a loss of nociception.


In modern anesthesia, a wide variety of medical equipment is desirable depending on the necessity for portable field use, surgical operations or intensive care support, and the type(s) of anesthetic(s) to be administered. Anesthesia practitioners must possess a comprehensive and intricate knowledge of the production and use of various medical gases, anesthetic agents and vapors, medical breathing circuits and the variety of anesthetic machines (including vaporizers, ventilators and pressure gauges) and their corresponding safety features, hazards and limitations of each piece of equipment, for the safe, clinical competence and practical application for day to day practice.

The risk of transmission of infection by anesthetic equipment has been a problem since the beginnings of anesthesia. Although most equipment that comes into contact with patients is disposable, there is still a risk of contamination from the anesthetic machine itself[22] or because of bacterial passage through protective filters.[23]


Patients under general anesthesia must undergo continuous physiological monitoring to ensure safety. In the US, the American Society of Anesthesiologists (ASA) have established minimum monitoring guidelines for patients receiving general anesthesia, regional anesthesia, or sedation. This includes electrocardiography (ECG), heart rate, blood pressure, inspired and expired gases, oxygen saturation of the blood (pulse oximetry), and temperature.[7] 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.

Effective July 1, 2011 the ASA implemented updated standards for patient monitoring.[24]


The anesthesia record is the medical and legal documentation of events while a patient is under anesthesia.[25] It should contain a detailed and continuous account of all drugs, fluids, and blood products administered and procedures undertaken, and also includes the observation of cardiovascular responses, estimated blood loss, urine output and data from physiologic monitors while a patient is under anesthesia.

Traditionally handwritten on paper, the anesthesia record is increasingly being replaced by an electronic record as part of an Anesthesia Information Management System (AIMS), especially since 2007.[26] An AIMS is any information system that is used as an automated electronic anesthesia record keeper (i.e., connection to patient physiologic monitors and/or the anesthetic machine) and which also may allow the collection and analysis of anesthesia-related perioperative patient data gathered from monitors and/or the anesthesia machine. These systems typically run on medical-grade hardware in the operating room. AIMS can be stand-alone systems or integrated modules of a hospital information system. AIMS have several benefits to the anesthesia departments as well to the hospital administration as documented in the scientific literature:

  • Reducing anesthesia-related drug costs[27]
  • Increased anesthesia billing and capture of anesthesia-related charges[28]
  • Increased hospital reimbursement through improved hospital coding[29][30]
  • Improved efficiency of the physicians involved in anesthesia and surgery through transfer pricing[31]
  • Improvement of the data quality of the intraoperative anesthesia record[32][33]
  • Support training and education of the anesthesia workforce[34]
  • Support of clinical decision-making[35]
  • Support of patient care and safety[36]
  • Enhancement of clinical studies[37]
  • Enhancement of clinical quality improvement programs[38]
  • Support of clinical risk management[39]
  • Monitoring for diversion of controlled substances[40]


Main articles: History of general anesthesia and History of neuraxial anesthesia

Plant derivatives

Throughout Europe, Asia, and the Americas a variety of Solanum species containing potent tropane alkaloids were used, such as mandrake, henbane, Datura metel, and Datura inoxia. Ancient Greek and Roman medical texts by Hippocrates, Theophrastus, Aulus Cornelius Celsus, Pedanius Dioscorides, and Pliny the Elder discussed the use of opium and Solanum species. 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 nineteenth century. In the Americas coca was also an important anesthetic used in trephining operations. Incan shamans chewed coca leaves and performed operations on the skull while spitting into the wounds they had inflicted to anesthetize the site.[41] Alcohol was also used, its vasodilatory properties being unknown. Ancient herbal anesthetics have variously been called soporifics, anodynes, and narcotics, depending on whether the emphasis is on producing unconsciousness or relieving pain.

The use of herbal anesthesia had a crucial drawback compared to modern practice—as lamented by Fallopius, "When soporifics are weak, they are useless, and when strong, they kill." To overcome this, production was typically standardized as much as feasible, with production occurring from specific locations (such as opium from the fields of Thebes in ancient Egypt). Anesthetics were sometimes administered in the "spongia somnifera", a sponge into which a large quantity of drug was allowed to dry, from which a saturated solution could be trickled into the nose of the patient. At least in more recent centuries, trade was often highly standardized, with the drying and packing of opium in standard chests, for example. In the 19th century, varying aconitum alkaloids from a variety of species were standardized by testing with guinea pigs. Trumping this method was the discovery of morphine, a purified alkaloid that could be injected by hypodermic needle for a consistent dosage. The enthusiastic reception of morphine led to the foundation of the modern pharmaceutical industry.[42]

The first effective local anesthetic was cocaine. Isolated in 1859, it was first used by Karl Koller, at the suggestion of Sigmund Freud, in eye surgery in 1884.[43] German surgeon August Bier (1861–1949) was the first to use cocaine for intrathecal anesthesia in 1898.[44] Romanian surgeon Nicolae Racoviceanu-Piteşti (1860–1942) was the first to use opioids for intrathecal analgesia; he presented his experience in Paris in 1901.[45] A number of newer local anesthetic agents, many of them derivatives of cocaine, were synthesized in the 20th century, including eucaine (1900), amylocaine (1904), procaine (1905), and lidocaine (1943).

Early inhalational anesthetics

Further information: Inhalational anesthetic

Early Arab writings mention anesthesia by inhalation. This idea was the basis of the "soporific sponge" ("sleep sponge"), introduced by the Salerno school of medicine in the late twelfth century and by Ugo Borgognoni (1180–1258) in the thirteenth 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 patient unconscious.

In 1275, Spanish physician Raymond Lullus, while experimenting with chemicals, made a volatile, flammable liquid he called sweet vitriol. Sweet vitriol, or sweet oil of vitriol, was the first inhalational anesthetic used for surgical anesthesia. It is no longer used often because of its flammability. In the 16th century, a Swiss-born physician commonly known as Paracelsus made chickens breathe sweet vitriol and noted that they not only fell asleep but also felt no pain. Like Lullus before him, he did not experiment on humans. In 1730, German chemist Frobenius gave this liquid its present name, ether, which is Greek for “heavenly.” But 112 more years would pass before ether’s anesthetic powers were fully appreciated.

Meanwhile, in 1772, English scientist Joseph Priestley discovered the gas nitrous oxide. Initially, people thought this gas to be lethal, even in small doses. 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. Davy wrote about the potential anesthetic properties of nitrous oxide, but nobody at that time pursued the matter any further.

American physician Crawford W. Long noticed that his friends felt no pain when they injured themselves while staggering around under the influence of 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.[46]

William Thomas Green Morton, a Boston dentist, conducted the first public demonstration of the inhalational anesthetic. 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".[47]

Morton at first attempted to hide the actual nature of his anesthetic substance, referring to it as Letheon. He received a US patent for his substance, but news of the successful anesthetic spread quickly by late 1846. Respected surgeons in Europe including Liston, Dieffenbach, Pirogov, and Syme, quickly undertook numerous operations with ether. An American-born physician, Boott, encouraged London dentist James Robinson to perform a dental procedure on a Miss Lonsdale. This was the first case of an operator-anesthetist. On the same day, 19 December 1846, in Dumfries Royal Infirmary, Scotland, a Dr. Scott used ether for a surgical procedure. 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 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 (1803-73) in Germany. Chloroform was named and chemically characterised in 1834 by Jean-Baptiste Dumas (1800-84). Its anaesthetic properties were noted early in 1847 by Marie-Jean-Pierre Flourens (1794-1867). The use of chloroform in anesthesia is linked to James Young Simpson, who, in a wide-ranging study of organic compounds, found chloroform's efficacy on 4 November 1847. Its use spread quickly and gained royal approval in 1853 when John Snow gave it to Queen Victoria during the birth of Prince Leopold. Unfortunately, chloroform is not as safe an agent as ether, especially when administered by an untrained practitioner (medical students, nurses, and occasionally members of the public were often pressed into giving anesthetics at this time). This led to many deaths from the use of chloroform that (with hindsight) might have been preventable. The first fatality directly attributed to chloroform anesthesia was recorded on 28 January 1848 after the death of Hannah Greener.

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.

See also

Main article: Outline of anesthesia


Further reading

  • McGrew, Roderick. Encyclopedia of Medical History (1985), brief history pp 14-18
  • Wolf, Jacqueline H. Deliver Me from Pain: Anesthesia and Birth in America (Johns Hopkins University Press, 2009) 277pp; covers 1840s to 21st century; ISBN 978-0-8018-9110-6

External links

  • Australian Society Of Anaesthesia Paramedical Officers
  • American Association of Nurse Anesthetists
  • American Society of Anesthesiologists
  • American Academy of Anesthesiologist Assistants
  • AnaesthesiaUK
  • Nova Southeastern University


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