Sedation is a medical procedure involving the administration of sedative drugs, generally to facilitate a medical procedure with local anesthesia.

		1 Uses
		2 Risks
		3 Levels of sedation

Uses

Sedation is typically used in procedures such as endoscopy, vasectomy, or minor surgery and in dentistry for reconstructive surgery, removal of impacted wisdom teeth, or for high-anxiety patients. Sedation methods in dentistry include inhalation sedation (using nitrous oxide), oral sedation, and intravenous (IV) sedation. Inhalation sedation is also sometimes referred to as Relative Analgesia.

Sedation is also used extensively in the intensive care unit so that patients who are being ventilated tolerate having an endotracheal tube in their trachea.

Risks

Airway obstruction, apnoea and hypotension are not uncommon during sedation and require the presence of health professionals who are suitably trained to detect and manage these problems.

Levels of sedation

Sedation scales are used in medical situations in conjunction with medical history to assess the degree of sedation in patients to avoid under-sedation (where the patient would experience pain or distress) and over-sedation (where the risk of side effects such as suppression of breathing might lead to death). Typically, levels are agitation, calm, responsive to voice only, to shaking only, to pain only and no response.

Anesthesia or anaesthesia (see spelling differences) has traditionally meant 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. It comes from the Greek roots an-, "not, without" and aesthetos, "perceptible, able to feel". The word was coined by Oliver Wendell Holmes, Sr. in 1846.

Today, the term general anesthesia in its most general form can include:

		Analgesia - blocking the conscious perception of pain
		Hypnosis - producing unconsciousness
		Amnesia - preventing memory formation
		Relaxation - preventing unwanted movement or muscle tone
		Homeostasis - preserving normal body functioning (e.g., maintaining blood pressure within normal physiological range)

There are several forms of anesthesia:

		general anesthesia — with reversible loss of consciousness and memory of unpleasant events
		local anesthesia — with reversible loss of sensation in a 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 blockage of sections of the spinal cord or nerves supplying the region. The administration of drugs to make a patient more comfortable or less anxious, but without inducing anesthesia, is called sedation.

General anesthesia

In modern medical practice, general anesthesia is a state of total unconsciousness resulting from general anesthetic drugs. A variety of drugs are given to the patient that have different effects with the overall aim of ensuring unconsciousness, amnesia and analgesia. The anesthetist (AmE: anesthesiologist) selects the optimal technique for any given patient and procedure.

General anesthesia is a complex procedure involving:

		Preanesthetic assessment
		Administration of general anesthetic drugs
		Cardiorespiratory monitoring
		Analgesia
		Airway management
		Fluid management
		Postoperative pain relief

Preanesthetic Evaluation

Prior to surgery, the anesthetist interviews the patient to determine the best combination and drugs and dosages and the degree of how much monitoring is required to ensure a safe and effective procedure.

Pertinent information is the patient's age, weight, medical history, current medications, previous anesthetics, and fasting time. Usually, the patients are required to fill out this information on a separate form during the pre-operative evaluation. Depending on the existing medical conditions reported, the anesthetist will review this information with the patient either during his pre-operative evaluation or on the day of his surgery.

Truthful and accurate answering of the questions is important so the anesthetist can select the proper anesthetics. For instance, a heavy drinker or drug user who does not disclose their chemical uses could be undermedicated, which could then lead to anesthesia awareness or dangerously high blood pressure.

An important aspect of this assessment is that of the patient's airway, involving inspection of the mouth opening and visualisation of the soft tissues of the pharynx. The condition of teeth and location of dental crowns and caps are checked, neck flexibility and head extension observed. If an endotracheal tube is indicated and airway management is deemed difficult, then alternative placement methods such as fiberoptic intubation may be used.

Premedication

Anesthetists may give a pre-medication ('pre-med') by injection, or more usually, tablets a couple of hours before surgery to induce drowsiness and relaxation. Pain killers (analgesics) may also be administered at this time. Pre-med's are not routinely used in modern anesthesia, but are still common.

Induction

The general anesthetic is administered in either the operating theatre itself or a special ante-room. General anesthesia can be induced by intravenous (IV) injection, or breathing a volatile anesthetic through a facemask (inhalational induction). Onset of anesthesia is faster with IV injection than with inhalation, taking about 10-20 seconds to induce total unconsciousness. This has the advantage of avoiding the excitatory phase of anesthesia (see below), and thus reduces complications related to induction of anesthesia. An inhalational induction may be chosen by the anesthetist where IV access is difficult to obtain, where difficulty maintaining the airway is anticipated, or due to patient preference (eg. children). Commonly used IV induction agents include propofol, sodium thiopental, etomidate, and ketamine.

Maintenance

The duration of action of IV induction agents is generally 5 to 10 minutes, after which time spontaneous recovery of consciousness will occur. In order to prolong anesthesia for the required duration (usually the duration of surgery), anesthesia must be maintained. Usually this is achieved by allowing the patient to breathe a carefully controlled mixture of oxygen and a volatile anesthetic agent. This is transferred to the patient's brain via the lungs and the bloodstream, and the patient remains unconscious. At the end of surgery the volatile anesthetic is discontinued. Recovery of consciousness occurs when the concentration of anesthetic in the brain drops below a certain level (usually within 1 to 30 minutes depending upon the duration of surgery).

In the 1990s a novel method of maintaining anesthesia was developed in Glasgow, UK. Called Total IntraVenous anesthesia (TIVA), this involves using a computer controlled syringe driver (pump) to infuse propofol throughout the duration of surgery, removing the need for a volatile anesthetic. Purported advantages include faster recovery from anesthesia, reduced incidence of post-operative nausea and vomiting, and absence of a trigger for malignant hyperthermia. 

Paralysis

The induction of paralysis with a neuromuscular blocker is an integral part of modern anesthesia. The first drug used for this purpose was curare, introduced in the 1940's and has now superseded with drugs with fewer side effects and generally shorter duration of action.

Paralysis allows surgery within major body cavities, eg. abdomen and thorax without the need for very deep anesthesia, and is also used to facilitate endotracheal intubation. Acetylcholine, the natural neurotransmitter substance at the neuromuscular junction, causes muscles to contract when it is released from nerve endings. Muscle relaxants work by preventing acetylcholine from attaching to its receptor.

Paralysis of the muscles of respiration, ie. the diaphragm and intercostal muscles of the chest requires that some form of artificial respiration be implemented. As the muscles of the larynx are also paralysed, the airway usually needs to be protected by means of an endotracheal tube.

Monitoring of paralysis is most easily provided 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 termination of surgery by anticholinesterase drugs.

Examples of skeletal muscle relaxants in use today are pancuronium, rocuronium, vecuronium, atracurium, mivacurium, and succinylcholine.

Airway management

With the loss of consciousness caused by general anesthesia, there is loss of protective airway reflexes (such as coughing), loss of airway patency and sometimes loss of a regular breathing pattern due to the effect of anesthetics, opioids, or muscle relaxants. To maintain an open airway and regulate breathing within acceptable parameters, some form of "breathing tube" is inserted in the airway after the patient is unconscious. To enable mechanical ventilation, an endotracheal tube is often used (intubation), although there are alternative devices such as face masks or laryngeal mask airways.

Monitoring

Monitoring involves the use of several technologies to allow for a controlled induction of, maintenance of and emergence from general anesthesia.

Stage 1

Stage 1 anesthesia, also known as the "induction," is the period between the initial administration of the induction medications 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 the time.

Stage 2

Stage 2 anesthesia, also known as the "excitement stage," is the period following loss of consciousness and marked by excited and delirious activity. During this stage, respirations and heart rate may become irregular. In addition, there may be uncontrolled movements, vomiting, breath holding, and pupillary stage3 Since the combination of spastic movements, vomiting, and irregular respirations may lead to airway compromise, rapidly acting drugs are used to minimize time in this stage and reach stage 3 as fast as possible.

Stage 3

Stage 3 anesthesia, also known as "surgical plane," follows the excitement stage and is marked by a return of regular respirations. This stage is divided into 4 planes based on changes to eye reflexes, eye movements, and pupil size. The ideal plane for surgery is plane 3 where the patient has minimal use of the respiratory muscles. The main indicators of the stages of anesthesia are the patient's respiratory and cardiovascular response to stimulation.

Stage 4

Stage 4 anesthesia, also known as "overdose," is the stage where too much medication has been given and the patient has severe brain stem or medullary depression. This results in a cessation of respiration and potential cardiovascular collapse. This stage is lethal without cardiovascular and respiratory support.

Postoperative Analgesia

The anesthesia concludes with a management plan for postoperative pain relief. This may be in the form of regional analgesia, oral or parenteral medication. Minor surgical procedures are amenable to oral pain relief medications such as paracetamol and NSAIDS such as ibuprofen. Moderate levels of pain require the addition of mild opiates such as codeine. Major surgical procedures may require a combination of modalities to confer adequate pain relief. Parenteral methods include Patient Controlled Analgesia System (PCAS) involving morphine, a strong opiate. Here, the patient presses a button to activate a pump containing morphine. This administers a preset dose of the drug. As the pump is programmed not to exceed a safe amount of the drug, the patient cannot self administer a toxic dose.

Mortality rates

Overall, the mortality rate for general anesthesia is about five deaths per million anesthetic administrations.[1] Death during anesthesia is most commonly related to surgical factors or pre-existing medical conditions. These include major hemorrhage, sepsis, and organ failure (eg. heart, lungs, kidneys,
liver).

Common causes of death directly related to anesthesia include:

		aspiration of stomach contents
		suffocation (due to inadequate airway management)
		allergic reactions to anesthesia (specifically and not limited to anti-nausea agents) and other deadly genetic predispositions
		human error
		equipment failure

Local anesthesia

Local anesthesia is any technique to render part of the body insensitive to pain without affecting
consciousness.

		Local anesthesia, in a strict sense, is anesthesia of a small part of the body such as a tooth or an area of skin.
		Regional anesthesia is aimed at anesthetizing a larger part of the body such as a leg or arm.
		Conduction anesthesia is a comprehensive term which encompasses a great variety of local and regional anesthetic techniques.

Conduction anesthesia

Conduction anesthesia allows patients to undergo many surgical procedures without significant pain or distress. In many situations, such as cesarean section), conduction anesthesia is safer and therefore superior to general anesthesia. In other situations, either conduction or general anesthesia are suitable. Anesthetists sometimes combine both techniques.

Conduction anesthesia is also used for relief of non-surgical pain, also to enable diagnosis of the cause of some chronic pain conditions.

The most common form of conduction anesthesia is probably local anesthesia to enable dental procedures.

Techniques

To achieve conduction anesthesia a local anesthetic is injected or applied to a body surface. The local anesthetic then diffuses into nerves where it inhibits the propagation of signals for pain, muscle contraction, regulation of blood circulation and other body functions. Relatively high drug doses or concentrations inhibit all qualities of sensation (pain, touch, temperature etc.) as well as muscle control. Lower doses or concentrations may selectively inhibit pain sensation with minimal effect on muscle power. Some techniques of pain therapy, such as walking epidurals for labor pain use this effect, termed differential block.

Anesthesia persists as long as there is a sufficient concentration of local anesthetic at the affected nerves. Sometimes a vasoconstrictor drug is added to decrease local blood flow, thereby slowing the transport of the local anesthetic away from the site of injection. Depending on the drug and technique, the anesthetic effect may persist from less than an hour to several hours. Placement of a catheter for continuous infusion or repeated injection allows conduction anesthesia to last for days or weeks. This is typically done for purposes of pain therapy.

Local anesthetics can block almost every nerve between the peripheral nerve endings and the central nervous system. The most peripheral technique is topical anesthesia to the skin or other body surface. Small and large peripheral nerves can be anesthetized individually (peripheral nerve block) or in anatomic nerve bundles (plexus anesthesia). Spinal anesthesia and epidural anesthesia are applied near the spinal cord where the peripheral nervous system merges into the central nervous system.

Clinical techniques include:

		Surface anesthesia - application of local anesthetic spray, solution or cream to the skin or a mucous membrane. The effect is short lasting and is limited to the area of contact.
		Infiltration anesthesia - injection of local anesthetic into the tissue to be anesthetized. Surface and infiltration anesthesia are collectively topical anesthesia.
		Field block - subcutaneous injection of a local anesthetic in an area bordering on the field to be anesthetized.
		Peripheral nerve blocks - injection of local anesthetic in the vicinity of a peripheral nerve to anesthetize that nerve's area of innervation.
		Plexus anesthesia - injection of local anesthetic in the vicinity of a nerve plexus, often inside a tissue compartment that limits the diffusion of the drug away from the intended site of action. The anesthetic effect extends to the innervation areas of several or all nerves stemming from the plexus.
		Epidural anesthesia - a local anesthetic is injected into the epidural space where it acts primarily on the spinal nerve roots. Depending on the site of injection and the volume injected, the anesthetized area varies from limited areas of the abdomen or chest to large regions of the body.
		Spinal anesthesia - a local anesthetic is injected into the cerebrospinal fluid, usually at the lumbar spine (in the lower back), where it acts on spinal nerve roots and part of the spinal cord. The resulting anesthesia usually extends from the legs to the abdomen or chest.
		Intravenous regional anesthesia (Bier's block) - blood circulation of a limb is interrupted using a tourniquet (a device similar to a blood pressure cuff), then a large volume of local anesthetic is injected into a peripheral vein. The drug fills the limb's venous system and diffuses into tissues where peripheral nerves and nerve endings are anesthetized. The anesthetic effect is limited to the area that is excluded from blood circulation and resolves quickly once circulation is restored.
		Local anesthesia of body cavities (e.g. intrapleural anesthesia, intraarticular anesthesia)

Regional anesthesia

Regional anesthesia is anesthesia affecting only a part of the body (not the brain). This term encompasses several techniques including epidural anesthesia and spinal anesthesia and conduction techniques where local anesthetics are injected around nerves leading to and from specific areas such as arms and legs. Additionally, there is a popular regional anesthesia technique called a Bier block pronounced Beer Block which is classified as an intravenous regional anesthetic.

Regional anesthesia involves the introduction of drugs, e.g. local anesthetics, with the intention of blocking the nerve supply to a specific part of the body, such as a limb, so the patient cannot feel pain during or after a surgical operation, for pain relief during onset of labor or during labor or for chronic pain. Unlike general anesthesia, the patient remains awake for the duration (or sedated), resulting in reduced side-effects and enabling the surgeon to converse with the patient during the procedure if required.

Examples of common regional anesthesia procedures are brachial plexus block for shoulder and arm procedures, femoral nerve and sciatic nerve block for leg procedures.

Regional anesthesia is now more common than general anesthesia for caesarian section procedures. An example of popular use is the application of epidural or combined spinal epidurals as a form of regional anesthesia favored during pregnancy near term or during labor.

Uses of Anesthesia

Anesthesia in surgery and dentistry

Virtually every part of the body can be anesthetized using conduction anesthesia. However, only a limited number of techniques are in common clinical use. Sometimes conduction anesthesia is combined with general anesthesia or sedation for the patient's comfort and ease of surgery. Typical operations performed under conduction anesthesia include:

		Dentistry (surface anesthesia, infiltration anesthesia, nerve blocks)
		Eye surgery (surface anesthesia with topical anesthetics, retrobulbar block)
		ENT operations, head and neck surgery (infiltration anesthesia, field blocks, peripheral nerve blocks, plexus anesthesia)
		Shoulder and arm surgery (plexus anesthesia, intravenous regional anesthesia)
		Heart and lung surgery (epidural anesthesia combined with general anesthesia)
		Abdominal surgery (epidural/spinal anesthesia, often combined with general anesthesia)
		Gynecological, obstetrical and urological operations (spinal/epidural anesthesia)
		Bone and joint surgery of the pelvis, hip and leg (spinal/epidural anesthesia, peripheral nerve blocks, intravenous regional anesthesia)
		Surgery of skin and peripheral blood vessels (topical anesthesia, field blocks, peripheral nerve blocks, spinal/epidural anesthesia)

Uses in acute pain

Acute pain may occur due to trauma, surgery, infection, disruption of blood circulation or many other conditions in which there is tissue injury. In a medical setting it is usually desirable to alleviate pain when its warning function is no longer needed. Besides improving patient comfort, pain therapy can also reduce harmful physiological consequences of untreated pain.

Acute pain can often be managed using analgesics. However, conduction anesthesia may be preferable because of superior pain control and fewer side effects. For purposes of pain therapy, local anesthetic drugs are often given by repeated injection or continuous infusion through a catheter. Low doses of local anesthetic drugs can be sufficient so that muscle weakness does not occur and patients may be mobilized.

Some typical uses of conduction anesthesia for acute pain are:

		Surgery of skin and peripheral blood vessels (topical anesthesia, field blocks, peripheral nerve blocks, spinal/epidural anesthesia)
		Labor pain (epidural anesthesia)
		Postoperative pain (peripheral nerve blocks, epidural anesthesia)
		Trauma (peripheral nerve blocks, intravenous regional anesthesia, epidural anesthesia)

Uses in chronic pain

Chronic pain of more than minor intensity is a complex and often serious condition that requires diagnosis and treatment by an expert in pain medicine. Local anesthetics can be applied repeatedly or continuously for prolonged periods to relieve chronic pain, usually in combination with medication such as opioids, NSAIDs, and anticonvulsants.

Miscellaneous uses

Topical anesthesia, in the form of lidocaine/prilocaine (EMLA) is most commonly used to enable relatively painless venipuncture (blood collection) and placement of intravenous cannulae. It may also be suitable for other kinds of punctures such as ascites drainage and amniocentesis.

Surface anesthesia also facilitates some endoscopic procedures such as bronchoscopy (visualization of the lower airways) or cystoscopy (visualization of the inner surface of the bladder).

History of Anesthesia

The leaves of the coca plant were traditionally used as a stimulant in Peru. It is believed that the local anesthetic effect of coca was also known and used for medical purposes. Cocaine was isolated in 1860 and first used as a local anesthetic in 1884. The search for a less toxic and less addictive substitute led to the development of the administer local anesthetic procaine in 1904. Since then, several synthetic local anesthetic drugs have been developed and put into clinical use, notably lidocaine in 1943, bupivacaine in 1957 and prilocaine in 1959.

Shortly after the first use of cocaine for topical anesthesia, blocks on peripheral nerves were described. Brachial plexus anesthesia by percutaneous injection through axillary and supraclavicular approaches was developed in the early 20th century. The search for the most effective and least traumatic approach for plexus anesthesia and peripheral nerve blocks continues to this day. In recent decades, continuous regional anesthesia using catheters and automatic pumps has evolved as a method of pain therapy.

Intravenous regional anesthesia was first described by August Bier in 1908. This technique is still in use and is remarkably safe when drugs of low systemic toxicity such as prilocaine are used. Spinal anesthesia was first used in 1885 but not introduced into clinical practice until 1899, when August Bier subjected himself to a clinical experiment in which he observed the anesthetic effect, but also the typical side effect of postpunctural headache. Within few years, spinal anesthesia became widely used for surgical anesthesia and was accepted as a safe and effective technique. Although atraumatic (non-cutting-tip) cannulas and modern drugs are used today, the technique has otherwise changed very little over many decades.

Epidural anesthesia by a caudal approach had been known in the early 20th century, but a well-defined technique using lumbar injection was not developed until the 1930s. With the advent of thin flexible catheters, continuous infusion and repeated injections have become possible, making epidural anesthesia a highly successful technique to this day. Beside its many uses for surgery, epidural anesthesia is particularly popular in obstetrics for the treatment of labor pain.

Anesthesia was used as early back as the classical age. Dioscorides, for example, reports potions being prepared from opium and mandragora as surgical anesthetics.

In the East, in the 10th century work Shahnama, 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.

Non-pharmacological methods

Hypnotism and acupuncture have a long history of use as anesthetic techniques. In China, Taoist medical practitioners developed anesthesia by means of acupuncture. Chilling tissue (e.g. with ice) can temporarily cause nerve fibres (axons) to stop conducting sensation, while hyperventilation can cause brief alteration in conscious perception of stimuli including pain. In modern anesthetic practice, these techniques are seldom employed.

Herbal derivatives

The first herbal anesthesia was administered in prehistory. Opium and Cannabis 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 early America preparations from datura - effectively scopolamine – were used as was coca. In Medieval Europe various preparations of mandrake were tried as was henbane (hyoscyamine). In 1804, the Japanese surgeon Hanaoka Seishu- performed general anesthesia 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."  He used a compound he called Tsusensan, based on the plants Datura metel, Aconitum and others.

Early gases and vapors

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 anesthetic 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, diethyl ether (discovered in 1540). In March 1842 in Danielsville, Georgia, Dr. Crawford Williamson Long was the first to use anesthesia 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 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 undergoing an excision of a tumor from his neck. In a letter to Morton shortly thereafter, Oliver Wendell Holmes, Sr. proposed naming the procedure anesthesia.

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 has a number of drawbacks, like its tendency to induce vomiting and its flammability. In England it was quickly replaced with chloroform. Discovered in 1831, its use in anesthesia 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. 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 which (with hindsight) might have been preventable.

The surgical amphitheater at Massachusetts General Hospital, or "ether dome" still exists today, although it is used for lectures and not surgery. The public can visit the amphitheater on weekdays when it is not in use.

Anesthetists, Anesthesiologists and the profession

Physicians specializing in peri-operative care, development of an anesthetic plan, and the administration of anesthetics are known as anaesthetists in the UK or, in the U.S., anesthesiologists. As with other specialties within medicine, doctors wishing to specialize in anesthesia must undertake extensive training. The length of this training varies by country, but is typically several years. In the U.S., the training of a physician anesthesiologist typically consists of 4 years of college, 4 years of medical school, 1 year of internship, and 3 years of residency. In the UK this training lasts a minimum of seven years after the awarding of a medical degree, 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.

Other countries have similar systems, including Ireland (the Faculty of Anaesthetists of the Royal
College of Surgeons in Ireland), Canada and South Africa.

These colleges typically set rigorous examinations, which must be passed before training is complete. These examinations encompass the whole field of anesthetic practice, and are usually split into several parts. 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 anesthesiolgist allows one to be called "Board Certified".

Other specialties within medicine are closely affiliated to anesthetics. These include intensive care medicine and pain medicine. Specialists in these disciplines have usually done some training in anesthetics. The role of the anesthetist is changing. It is no longer limited to the operation itself. Many anesthetists 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 anesthetic, following up the patient in the post anesthesia care unit and post-operative wards, and ensuring optimal analgesia throughout.

In the U.S., nurse practitioners specializing in anesthetics are known as CRNAs. Anesthesiologist Assistants are another group who administer anesthetics. In the United Kingdom, personnel known as ODPs (operating department practitioner) or Anaesthetic nurses provide support to the anaesthetist. All anaesthetics in the UK, Australia and New Zealand are administered by physicians.

Anesthetic equipment and physics

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. 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.

Local anesthetics

The first effective local anesthetic was cocaine. Isolated in 1859 it was first used by Karl Koller, at the suggestion of Sigmund Freud, in ophthalmic surgery in 1884. Before 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).

Local anesthetics are agents which prevent transmission of nerve impulses without causing unconsciousness. They act by binding to fast Sodium channels from within (in an open state).

Classification: Local anesthetics can be either ester or amide based.

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

- Amide local anesthetics (eg. lidocaine, prilocaine, bupivicaine, levobupivacaine, ropivacaine, dibucaine) are generally heat stable with a long shelf life of 2 years, with a slower onset (longer half life) and are usually a racemic mixture (with the exceptions being levobupivacaine which is S(-)-bupivacaine, and ropivacaine, which is actually S(-)-ropivacaine). It is this type of local anesthetic agent that is generally used within regional and epidural/spinal techniques namely due to their longer duration of action providing adequate analgesia suitable for surgery, labor and symptomatic relief.

NB: Only local anesthetic agents that are preservative free may be injected intrathecally (i.e within the subarachnoid space).

Adverse Effects Of Local anesthesia

Local anesthetic drugs are toxic to the heart (where they cause arrhythmia) and brain (where they cause unconsciousness and seizures). Arrhythmias may be resistant to defibrillation and other standard treatments, and may lead to loss of heart function and death.

The first evidence of local anesthetic toxicity involves the nervous system including agitation, confusion, dizziness, blurred vision, tinnitus, metallic taste in mouth, and nausea that can quickly progress to seizure and cardiovascular collapse.

Direct infiltration of local anesthetic into skeletal muscle will cause temporary paralysis of the muscle.

Toxicity can occur with any local anesthetic, and possible toxicity may be tested with pre-med procedures to avoid toxicity occuring during surgery.

Early opioids and hypnotics

Opioids were first used by Racoviceanu-Pites,ti, who reported his work in 1901.

Current inhaled general anesthetic agents

		Nitrous Oxide
		Halothane
		Enflurane
		Isoflurane
		Sevoflurane
		Desflurane
		Xenon (rarely used)

Current IV general or sedative agents

		Thiopental
		Methohexital
		Propofol
		Etomidate
		Ketamine
		Diazepam
		Midazolam

 Muscle relaxants

		Succinylcholine (also known as suxamethonium in the UK, New Zealand, Australia and other countries)
		Vecuronium
		Rocuronium
		Pancuronium
		Pipecuronium
		Rapacuronium
		Mivacurium
		Atracurium
		Cisatracurium
		Curare, the active ingredient of which is tubocurarine
		Metocurine
		Gallamine

Adverse effects of muscle relaxants

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

Another potentially disturbing adverse effect is Anesthesia awareness. In this situation, patients
paralyzed with muscle relaxants may awaken from their anesthesia. If this fact is missed by the
anesthesiologist, the patient may be aware of their surroundings, but be incapable of moving or
communicating that fact.

Opioid analgesics

		Morphine
		Diamorphine, (diacetyl morphine, also known as heroin)
		Codeine, (methyl morphine)
		Fentanyl
		Alfentanil
		Sufentanil
		Remifentanil
		Meperidine, also called pethidine in the UK, New Zealand, Australia and other countries
		Methadone
		Oxycodone
		Naloxone, although chemically similar to some analgesics, is not a painkiller and reverses the effects of morphine-like agents.

Volatile agents

These are specially formulated organic liquids, which evaporate readily into vapors, which are
given by inhalation for induction and/or maintenance of general anesthesia. The ideal anesthetic
vapor or gas should be non-flammable; non-explosive; lipid soluble; possess low blood gas
solubility; have no end organ (heart, liver, kidney) side effects; not be metabolized and be
non-irritant when breathed by patients.

No anesthetic vapor currently in use meets all of these requirements. The vapors in current use
are halothane, isoflurane, desflurane and sevoflurane. Nitrous oxide is still in widespread use,
making it one of the most long lived and successful drugs in use. Ether is still used in poorer
countries as it is cheap to manufacture and safe, particularly when administered by untrained
personnel.

In theory, any anesthetic vapor can be used for induction of general anesthesia. However, most of
the vapors are irritating to the airway, resulting in coughing, laryngospasm and overall difficult
inductions. Commonly used agents for inhalational induction include sevoflurane and halothane.
All of the modern vapors 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 gas is being pursued but it is very
expensive to produce, and requires special equipment for delivery, monitoring and scavenging of
unused 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 their versatility for a faster
emergence from anesthesia, thanks to their lower blood:gas partition coefficient.

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,
but there is no conclusive scientific evidence favoring one technique over the other. Neuraxial
blockade may reduce the risk of deep vein thrombosis, pulmonary embolism, blood transfusion,
pneumonia, respiratory depression, myocardial infarction and renal failure.

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