Science Fair Project Encyclopedia
Anesthesia (AE), also anaesthesia (BE), is the process of blocking the perception of pain and other sensations. This allows patients to undergo surgery and other procedures without the distress and pain they would otherwise experience. There are several forms of anesthesia:
- general anesthesia — with reversible loss of consciousness
- local anesthesia — with reversible loss of sensation in a (small) part of the body by localized administration of anesthetic drugs at the affected site.
- regional anesthesia — with reversible loss of sensation and possibly movement in a region of the body by selective blockade of sections of the spinal cord or nerves supplying the region.
Physicians specialising in the administration of anesthetics are known as anesthesiologists (AE) or anaesthetists (BE). Nurses specialising in the administration of anesthetics are known as nurse anesthetists (AE), who typically have gone to graduate school after nursing school, or have at least obtained certification as a CRNA (Certified Registered Nurse Anesthetist). "Anesthetist", despite typically referring to nurses, can refer to a physician or a nurse. Anesthesiologist Assisstants are another group of health care providers who administer anesthetics. They pursue a graduate degree in anesthesia from an accredited program and are supervised directly by an anesthesiologist.
The first herbal anaesthesia was administered in prehistory. Opium and hemp were two of the most important herbs used. They were ingested or burned and the smoke inhaled. Alcohol was also used, its vasodilatory properties being unknown. In China, Taoist medical practitioners developed anaesthesia by means of acupuncture. In South America preparations from datura, effectively scopolamine, were used as was coca. In Medieval Europe various preparations of mandrake were tried as was henbane (hyoscyamine).
Early gases and vapours
The development of effective anaesthetics 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 by Joseph Priestley) were discovered by the British chemist Humphry Davy about 1795 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 in December 1844 for painless tooth extraction by American dentist Horace Wells. Demonstrating it the following year, at Massachusetts General Hospital, he made a mistake and the patient suffered considerable pain. This lost Wells any support.
Another dentist, William E. Clarke , performed an extraction in January 1842 using a different chemical, sulfuric ether (discovered in 1540). In March 1842 in Danielsville, Georgia, Dr. Crawford Williamson Long was the first to use anaesthesia during an operation, giving it to a boy before excising a cyst from his neck; however, he did not publicize this information until later.
On the 16th of October 1846, another dentist, William Thomas Green Morton, invited to the Massachusetts General Hospital, performed the first public demonstration of sulfuric ether as an anesthetic agent, for a patient undergoing an excision of a tumour from his neck. In a letter to Morton shortly thereafter, Oliver Wendell Holmes, Sr. proposed naming the procedure anęsthesia.
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.
Ether had a number of drawbacks. In England it was quickly replaced with chloroform. Discovered in 1831, its use in anaesthesia is usually linked to James Young Simpson, who, in a wide-ranging study of organic compounds, found chloroform's efficacy in 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.
The first effective local anaesthetic was cocaine. Isolated in 1859 it was first used by Karl Koller in ophthalmic surgery in 1884. Prior to that doctors had used a salt and ice mix for the numbing effects of cold - which could only have limited application. Similar numbing was also induced by a spray of ether or ethyl chloride. Cocaine soon produced a number of derivatives and safer replacements, including procaine (1905), Eucaine (1900), Stovaine (1904), and lidocaine (1943).
The twentieth century
- MAC (minimum alveolar concentration) is defined as the percentage of inhalational agent required to stop 50% of people moving to a surgical stimulus, in the absence of nitrous oxide (a carrier gas) and an opioid premed.
- Thiopental (first used in 1934)
- Intravenous (Benzodiazepine)
- Propofol (2,6-di-isopropyl-phenol)
- Etomidate (an imidazole derivative)
- Ketamine (a phencyclidine derivative, as is 'Angel Dust/Special K')
- Curare (1942)
- Fentanyl (d 1960 Paul Janssen ) fentanyl citrate
- Halothane (d 1951 Charles W. Suckling , 1956 James Raventos ) MAC, non-explosive/non-flammable. Halothane hepatitis, malignant hyperthermia, hepatotoxic
- Enflurane (d 1963 u 1972), Isoflurane (d 1965 u 1971), Desflurane, Sevoflurane
- New synthetic opioids - meperidine, alfentanil, sufentanil (1981), remifentanil
Choice of anesthetic technique
The choice of anesthetic technique is a complex one, requiring consideration of both patient and surgical factors.
In certain patient populations, however, regional anesthesia may be safer than general anesthesia. Neuraxial blockade reduces the risk of deep vein thrombosis, pulmonary embolism, transfusion, pneumonia, respiratory depression, myocardial infarction and renal failure.
- Anesthesia awareness
- Latex allergy
- Allergic reactions during anaesthesia
- Malignant hyperthermia
- Postoperative nausea and vomiting
- Patient information
- American Society of Anaesthesiologists
- A medical student's guide to anaesthesia from a patient's perspective
- Gasnet, a comprehensive anaesthesiology resource
- Columbia Encyclopedia-Acupuncture
- University of California Pain Alleviation and Anesthesia Exhibit
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