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Anesthesiology is the science of Anesthesia or anaesthesia (see spelling differences; from Greek αν- an- “without” + αἲσθησις aisthesis “sensation”), the condition of having the feeling of pain and other sensations blocked. This allows patients to undergo surgery and other procedures without the distress and pain they would otherwise experience. The word was coined by Oliver Wendell Holmes, Sr., the American physician and poet, in 1846. Another definition is a "reversible lack of awareness", whether this is a total lack of awareness (e.g. a general anaesthestic) or a lack of awareness of a part of a the body such as a spinal anaesthetic or another nerve block would cause.


Patients undergoing surgery usually undergo preoperative evaluation by an anesthesiologist. It includes gathering history of previous anesthetics, and any other medical problems by the anesthesiologist MD, physical examination, ordering required blood work and consultations prior to surgery.


  • General anesthesia: "Drug-induced loss of consciousness during which patients are not arousable, even by painful stimulation." Patients undergoing general anesthesia often cannot maintain their own airway and breathe on their own. While usually administered with inhalational agents, general anesthesia can be achieved with intravenous agents, such as propofol.[1]


The following refer to states achieved by anesthetics working outside of the brain:



Herbal derivativesEdit

The first herbal anesthesia was administered in prehistory. Opium poppy capsules were collected in 4200 B.C., and opium poppies were farmed in Sumeria and succeeding empires. The use of opium-like preparations in anaesthesia is recorded in the Ebers Papyrus of 1500 B.C. By 1100 B.C. in Cyprus poppies were scored for collection of opium by methods similar to those used in the present day, and simple apparatus for smoking of opium was found in a Minoan temple. Opium was not introduced to India and China until 330 B.C. and 600-1200 A.D., but these nations pioneered the use of cannabis incense and aconitum. In the second century, according to the Book of Later Han, the physician Hua Tuo performed abdominal surgery using an anesthetic substance called mafeisan (麻沸散 "cannabis boil powder") dissolved in wine. 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. Classic 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, and treatment with the combined alkaloids proved a mainstay of anaesthesia until the nineteenth century. In the Americas coca was also an important anaesthetic used in trephining operations. Incan shamans chewed coca leaves and performed operations on the skull while spitting into the wounds they'd inflicted to anaesthetize the site.[How to reference and link to summary or text] Alcohol was also used, its vasodilatory properties being unknown. Ancient herbal anaesthetics have variously been called soporifics, anodynes, and narcotics, depending on whether the emphasis is on producing unconsciousness or relieving pain.

In the East, in the 10th century work Shahnameh, the author describes a caesarean section performed on Rudaba when giving birth, in which a special wine agent was prepared by a Zoroastrian priest, and used to produce unconsciousness for the operation. Although largely mythical in content, the passage does at least illustrate knowledge of anesthesia in ancient Persia. Dioscorides and other Greek authors were well-known in the Islamic Empire, and physicians such as al-Razi, Avicenna, and al-Qasim wrote textbooks of great importance in the development of medicine in medieval Europe.



In 1804, the Japanese surgeon Hanaoka Seishū performed general anaesthesia for the operation of a breast cancer (mastectomy), by combining Chinese herbal medicine know-how and Western surgery techniques learned through "Rangaku", or "Dutch studies". His patient was a 60-year-old woman called Kan Aiya.[3] He used a compound he called Tsusensan, based on the plants Datura metel, Aconitum and others.

Non-pharmacological methodsEdit


In modern anesthetic practice, these techniques are seldom employed.

Early gases and vapoursEdit

Southworth &amp; Hawes - First etherized operation (re-enactment)

Contemporary re-enactment of Morton's October 16, 1846, ether operation; daguerrotype by Southworth & Hawes.

In the West, the development of effective anesthetics in the 19th century was, with Listerian techniques, one of the keys to successful surgery. Henry Hill Hickman experimented with carbon dioxide in the 1820s. The anaesthetic qualities of nitrous oxide (isolated in 1773 by Joseph Priestley) were discovered by the British chemist Humphry Davy about 1799 when he was an assistant to Thomas Beddoes, and reported in a paper in 1800. But initially the medical uses of this so-called "laughing gas" were limited - its main role was in entertainment. It was used on 30 September 1846 for painless tooth extraction upon patient Eben Frost by American dentist William Thomas Green Morton. Horace Wells Connecticut, a travelling dentist, had demonstrated it the previous year 1845, at Massachusetts General Hospital. Wells made a mistake, in choosing a particularly sturdy male volunteer, and the patient suffered considerable pain. This lost the colourful Wells any support. Later the patient told Wells he screamed in shock and not in pain. A subsequently drunk Wells died in jail, by cutting his femoral artery, after allegedly assaulting a prostitute with sulphuric acid.

Another dentist, William E. Clarke, performed an extraction in January 1842 using a different chemical, diethyl ether (discovered by Valerius Cordus in 1540). In March 1842 in Danielsville, Georgia, Dr. Crawford Long was the first to use anaesthesia during an operation, giving it to a boy (John Venables) before excising a cyst from his neck; however, he did not publicize this information until later.

On October 16, 1846, another dentist, William Thomas Green Morton, invited to the Massachusetts General Hospital, performed the first public demonstration of diethyl ether (then called sulfuric ether) as an anesthetic agent, for a patient (Edward Gilbert Abbott) undergoing an excision of a vascular tumour from his neck. In a letter to Morton shortly thereafter, Oliver Wendell Holmes, Sr. proposed naming the procedure anæsthesia.


Anesthesia pioneer Crawford W. Long

Despite Morton's efforts to keep "his" compound a secret, which he named "Letheon" and for which he received a US patent, the news of the discovery and the nature of the compound spread very quickly to Europe in late 1846. Here, respected surgeons, including Liston, Dieffenbach, Pirogoff, and Syme undertook numerous operations with ether. An American born physician, Boott who had travelled to London, encouraged a leading dentist, Mr James Robinson, to perform a dental procedure on a Miss Lonsdale. This was the first case of an operator-anaesthetist. On the same day, Saturday 19 December 1846 in Dumfries Royal Infirmary, Scotland, A Dr Scott used ether for a surgical procedure. The first use of anaesthesia in the southern hemisphere took place in Launceston, Tasmania, that same year. Ether has a number of drawbacks, such as its tendency to induce vomiting and its flammability. In England it was quickly replaced with chloroform.

Discovered in 1831, the use of chloroform in anaesthesia is usually 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 anaesthetics at this time). This led to many deaths from the use of chloroform which (with hindsight) might have been preventable. The first fatality directly attributed to chloroform anaesthesia (Hannah Greener) was recorded on 28 January 1848.

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 inhalational anaesthesia.


Early local anestheticsEdit



Anesthesia ProvidersEdit

Physicians specialising in peri-operative care, development of an anesthetic plan, and the administration of anesthetics are known in the United States as anesthesiologists and in the UK and Canada as anaesthetists or anaesthesiologists. All anaesthetics in the UK, Australia, New Zealand and Japan are administered by physicians. Nurse anesthetists also administer anesthesia in 109 nations.[4] In the US, 35% of anesthetics are provided by physicians in solo practice, about 55% are provided by ACTs with anesthesiologists medically directing Anesthesiologist Assistants, CRNAs, and about 10% are provided by CRNAs in solo practice. [5] [6] [7] - [8] - [9]

Physician Anesthesiologists / Anaesthetists/ AnaesthesiologistsEdit

In the US, medical doctors who specialize in anesthesiology are called anesthesiologists. Such physicians in the UK and Canada are called anaesthetists or anaesthesiologists.

In the U.S., a physician specializing in anesthesiology completes 4 years of college, 4 years of medical school, 1 year of internship, and 3 years of residency. According to the American Society of Anesthesiologists, Anesthesiologists provide or participate in more than 90 percent of the 40 million anesthetics delivered annually.[10]


In the UK, completion of the examinations set by the Royal College of Anaesthetists leads to award of the Diploma of Fellowship of the Royal College of Anaesthetists (FRCA). In the US, completion of the written and oral Board examinations by a physician anesthesiologist allows one to be called "Board Certified" or a "Diplomate" of the American Board of Anesthesiology.

Other specialties within medicine are closely affiliated to anaesthetics. These include intensive care medicine and pain medicine. Specialists in these disciplines have usually done some training in anaesthetics. The role of the anaesthetist is changing. It is no longer limited to the operation itself. Many anaesthetists consider themselves to be peri-operative physicians, and will involve themselves in optimizing the patient's health before surgery (colloquially called "work-up"), performing the anaesthetic, following up the patient in the post anesthesia care unit and post-operative wards, and ensuring optimal analgesia throughout.

It is important to note that the term "anesthetist" in the United States usually refers to registered nurses who have completed specialized education and training in nurse anesthesia to become certified registered nurse anesthetists (CRNAs). As noted above, the term "anaesthetist" in the UK and Cananda refers to medical doctors who specialize in anesthesiology.

Nurse AnesthetistsEdit

In the United States, advance 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, CRNAs administer approximately 27 million anesthetics in the US each year.[[2]] CRNAs are the sole providers of anesthesia in more than 70 percent of rural area hospitals. Thirty-four percent of nurse anesthetists practice in communities of less than 50,000. CRNAs start school with a bachelors degree and at least 1 year of acute care nursing experience[[3]], and gain a masters degree in nurse anesthesia before passing the mandatory Certification Exam. The average CRNA student has 5-7 years of nursing experience before entering a 27-36 month masters level anesthesia program.[11]

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. The degree of physician supervision, direction, or collaboration required is determined by State law and hospital policy. Additionally, in order to participate in Medicare, federal regulations require collaboration with a physician, unless the governor of the State has chosen to opt out of this requirement.

Anesthesiology AssistantsEdit

In the US, Anesthesiologist Assistants (AAs) are physician assistants who have undertaken specialized education and training to provide anesthesia care. AAs typically hold a masters degree and practice under physician supervision in sixteen states through licensing, certification or physician delegation.[12]

In the UK, a similar group of assistants are currently being evaluated. In Scotland they are named Physician's Assistant - Anaesthesia and in the rest of the UK, they are called Anaesthesia Practitioners. Their background can be nursing, operating department professional or another profession allied to medicine or a science graduate. Training takes 27 months and to date, the first five have graduated in England.

Anesthesiology Assistants should be distinguished from Anesthesia Technicians.

Anesthesia TechniciansEdit



In the United Kingdom, personnel known as ODPs (operating department practitioners) or Anaesthetic nurses provide support to the physician anaesthetist (anaesthesiologist).

Veterinary Anesthetists / AnesthesiologistsEdit

Main article: Veterinary anesthesia


Anesthetic agents Edit

Local anestheticsEdit

Main article: Local anesthetic


Ester local anesthetics (eg. procaine, amethocaine, cocaine) are generally unstable in solution and fast acting, and allergic reactions are common.

Amide local anesthetics (eg. lidocaine, prilocaine, bupivicaine, levobupivacaine, ropivacaine and dibucaine) are generally heat stable, with a long shelf life (around 2 years). They have a slower onset and longer half life than ester anaesthetics, and are usually racemic mixtures, with the exception of levobupivacaine (which is S(-) -bupivacaine) and ropivacaine (S(-)-ropivacaine). These agents are generally used within regional and epidural or spinal techniques, due to their longer duration of action which provides adequate analgesia for surgery, labor and symptomatic relief.

Only preservative-free local anesthetic agents may be injected intrathecally.

Adverse effects of local anaesthesiaEdit





Current inhaled general anesthetic agentsEdit

Main article: General anaesthesia

Volatile agents are specially formulated organic liquids that evaporate readily into vapors, and are given by inhalation for induction and/or maintenance of general anesthesia. Nitrous oxide and xenon are gases at room temperature rather than liquids, so they are not considered volatile agents. The ideal anesthetic vapor or gas should be non-flammable, non-explosive, lipid soluble, should possess low blood gas solubility, have no end organ (heart, liver, kidney) toxicity or side effects, should not be metabolized and should be non-irritant when inhaled by patients.


In theory, any inhaled anesthetic agent can be used for induction of general anesthesia. However, most of the halogenated anesthetics are irritating to the airway, perhaps leading to coughing, laryngospasm and overall difficult inductions. For this reason, the most frequently-used agent for inhalational induction is sevoflurane. All of the volatile agents can be used alone or in combination with other medications to maintain anesthesia (nitrous oxide is not potent enough to be used as a sole agent).

Currently research into the use of xenon as an anesthetic is underway, but the gas is very expensive to produce and requires special equipment for delivery, as well as special monitoring and scavenging of waste gas.

Volatile agents are frequently compared in terms of potency, which is inversely proportional to the minimum alveolar concentration. Potency is directly related to lipid solubility. This is known as the Meyer-Overton hypothesis. However, certain pharmacokinetic properties of volatile agents have become another point of comparison. Most important of those properties is known as the blood:gas partition coefficient. This concept refers to the relative solubilty of a given agent in blood. Those agents with a lower blood solubility (i.e. a lower blood:gas partition coefficient, e.g. desflurane) give the anesthesia provider greater rapidity in titrating the depth of anesthesia, and permit a more rapid emergence from the anesthetic state upon discontinuing their administration. In fact, newer volatile agents (e.g. sevoflurane, desflurane) have been popular not due to their potency [minimum alveolar concentration], but due to their versatility for a faster emergence from anesthesia, thanks to their lower blood:gas partition coefficient.

Current intravenous anesthetic agents (non-opioid)Edit


The two barbiturates mentioned above, thiopental and methohexital, are ultra-short acting and are used to induce and maintain anesthesia.[14] However, though they produce unconsciousness, they provide no analgesia (pain relief) and must be used with other agents.[14] Benzodiazepines can be used for sedation before or after surgery and can be used to induce and maintain general anesthesia.[14] When benzodiazepines are used to induce general anesthesia, midazolam is preferred.[14] Benzodiazepines are also used for sedation during procedures that do not require general anesthesia.[14] Like barbiturates, benzodiazepines have no pain-relieving properties.[14] Propofol is one of the most commonly-used intravenous drugs employed to induce and maintain general anesthesia.[14] It can also be used for sedation during procedures or in the ICU.[14] Like the other agents mentioned above, it renders patients unconscious without producing pain relief.[14] Because of its favorable physiological effects, "etomidate has been primarily used in sick patients."[14] Ketamine is infrequently used in anesthesia practice because of the unpleasant experiences which sometimes occur upon emergence from anesthesia, which include "vivid dreaming, extracorporeal experiences (sense of floating out of one's body), and illusions (misinterpretation of a real, external sensory experience"[15] However, like etomidate it is frequently used in emergency settings and with sick patients because it produces fewer adverse physiological effects.[14] Unlike the intravenous anesthetic drugs previously mentioned, ketamine produces profound pain relief, even in doses lower than those which induce general anesthesia.[14] Also unlike the other anesthetic agents in this section, "patients who receive ketamine alone appear to be in a cataleptic state, unlike other states of anesthesia that resemble normal sleep. Ketamine-anesthetized patients have profound analgesia but keep their eyes open and maintain many reflexes."[14]

Current intravenous opioid analgesic agentsEdit

While opioids can produce unconsciousness, they do so unreliably and with significant side effects.[16][17] So, while they are rarely used to induce anesthesia, they are frequently used along with other agents such as intravenous non-opioid anesthetics or inhalational anesthetics.[14] Furthermore, they are used to relieve pain of patients before, during, or after surgery. The following opioids have short onset and duration of action and are frequently used during general anesthesia:


Current muscle relaxantsEdit


Adverse effects of muscle relaxantsEdit

Succinylcholine may cause hyperkalemia if given to burn patients, or paralyzed (quadraplegic, paraplegic) patients. The mechanism is reported to be through upregulation of acetylcholine receptors in those patient populations. Succinylcholine may also trigger malignant hyperthermia in susceptible patients.

Another potentially disturbing complication can be 'anesthesia awareness'. In this situation, patients paralyzed with muscle relaxants may awaken during their anesthesia, due to decrease in the levels of drugs providing sedation and/or pain relief. If this fact is missed by the anaesthesia provider, the patient may be aware of his surroundings, but be incapable of moving or communicating that fact. Neurological monitors are becoming increasingly available which may help decrease the incidence of awareness. Most of these monitors use proprietary algorithms monitoring brain activity via evoked potentials. Despite the widespread marketing of these devices many case reports exist in which awareness under anesthesia has occurred despite apparently adequate anesthesia as measured by the neurologic monitor. [How to reference and link to summary or text]

Current intravenous reversal agentsEdit

  • Naloxone, reverses the effects of opioids
  • Flumazenil, reverses the effects of benzodiazepines
  • Neostigmine, reverses the effects of non-depolarizing muscle relaxants

Anesthetic equipment Edit

Main article: Anaesthetic equipment


Anesthetic monitoringEdit

Patients being treated under general anesthetics must be monitored continuously to ensure the patient's safety. This will generally include monitoring of heart rate (via ECG), oxygen saturation (via pulse oximetry), blood pressure, inspired and expired gases (for oxygen, nitrous oxide, carbon dioxide, and volatile agents), and may also include monitoring of temperature, arterial blood pressure and waveforms, central venous pressure, cerebral activity (via EEG), neuromuscular activity (via peripheral nerve stimulation monitoring), cardiac output, and urine output. In addition, the operating room's environment must be monitored for temperature and humidity and for buildup of exhaled inhalational anesthetics which might impair the function of operating room personnel.

Anesthesia in popular cultureEdit

The 1958 film Corridors of Blood starring Boris Karloff depicts an 1840's surgeon who experiments with anesthetic gases in an effort to make surgery pain free. A bestseller by Robin Cook "Harmful Intent" has an anesthesiologist as the main character, who uncovers a legal conspiracy aimed at his specialty.

In the 2005 hit song Twisted Transistor, by nu metal group Korn, lead man Jonathan Davis says, "This won't hurt a bit... anesthetize this bitch".

Cliff Burton's bass solo on Metallica's Kill Em All is called, Anesthesia (Pulling Teeth).

See alsoEdit


  1. (2004) Continuum Of Depth Of Sedation Definition Of General Anesthesia And Levels Of Sedation/Analgesia. American Society of Anesthesiologists. [1]
  3. Utopian surgery: Early arguments against anaesthesiain surgery, dentistry and childbirth
  4. Nurse anestheisa worldwide: practice, education and regulation. (PDF) International Federation of Nurse Anesthetists. URL accessed on 2007-02-08.
  5. Is Physician Anesthesia Cost-Effective?. (html) Anesth Analg. URL accessed on 2007-02-15.
  6. When do anesthesiologists delegate?. (html) Med Care. URL accessed on 2007-02-15.
  8. Surgical mortality and type of anesthesia provider. (html) AANA. URL accessed on 2007-02-25.
  9. Anesthesia Providers, Patient Outcomes, and Cost. (pdf) Anesth Analg. URL accessed on 2007-02-25.
  10. ASA Fast Facts: Anesthesiologists Provide Or Participate In 90 Percent Of All Annual Anesthetics. (html) ASA. URL accessed on 2007-03-22.
  11. Television conferencing: Is it as effective as "in person" lectures for nurse anesthesia education?. (PDF) AANA Journal. URL accessed on 2007-02-05.
  12. Five facts about AAs. (HTML) American Academy of Anesthesiologist Assistants. URL accessed on 2007-02-08.
  13. 13.0 13.1 Townsend, Courtney (2004). Sabiston Textbook of Surgery, Chapter 17 – Anesthesiology Principles, Pain Management, and Conscious Sedation, Philadelphia: Saunders.
  14. 14.00 14.01 14.02 14.03 14.04 14.05 14.06 14.07 14.08 14.09 14.10 14.11 14.12 14.13 Miller, R., (2005), Miller's Anesthesia, NY: Elsevier/Churchill Livingstone, isbn 0443066566
  15. Garfield JM, Garfield FB, Stone JG, et al: A comparison of psychologic responses to ketamine and thiopental-nitrous oxide-halothane anesthesia. Anesthesiology 1972; 36:329-338.
  16. Philbin DM, Rosow CE, Schneider RC, et al: Fentanyl and sufentanil anesthesia revisited: how much is enough?. Anesthesiology 1990; 73:5-11.

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