In modern medical practice, general anaesthesia (AmE: anesthesia) is a state of total unconsciousness resulting from general anaesthetic 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 anaesthetist (AmE: anesthesiologist) selects the optimal technique for any given patient and procedure. English language spread in the United States. ... A general anaesthetic drug is an anaesthetic (or anesthetic AE) drug that brings about a reversible loss of consciousness. ... Unconsciousness is the absence of consciousness. ... Amnesia or amnaesia (see spelling differences) is a condition in which memory is disturbed. ... For other uses of painkiller, see painkiller (disambiguation) An analgesic (colloquially known as painkiller) is any member of the diverse group of drugs used to relieve pain. ... English language spread in the United States. ...

Overview

General anaesthesia is a complex procedure involving:

• Preanaesthetic assessment
• Administration of general anaesthetic drugs
• Cardiorespiratory monitoring
• Analgesia
• Airway management
• Fluid management
• Postoperative pain relief

A general anaesthetic drug is an anaesthetic (or anesthetic AE) drug that brings about a reversible loss of consciousness. ... To monitor or monitoring may mean: to observe a situation for any changes which may occur over time, using a monitor or measuring device of some sort: Baby monitor, medical monitor, Heart rate monitor Biomonitoring Condition monitoring Network monitoring Election monitoring to observe the behaviour or communications of individuals or... For other uses of painkiller, see painkiller (disambiguation) An analgesic (colloquially known as painkiller) is any member of the diverse group of drugs used to relieve pain. ... In cardiopulmonary resuscitation, anaesthesia, emergency medicine, and intensive care medicine, airway management is the process or ensuring that: there is an open pathway between a patient’s lungs and the outside world, and the lungs are safe from aspiration. ...

Preanaesthetic Evaluation

Prior to surgery, the anaesthetist interviews the patient to determine the best combination and drugs and doseages 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 anaesthetics, 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 anaesthetist 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 anaesthetist can select the proper anaesthetics. 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. Anesthesia awareness, or intra-operative awareness occurs during general anesthesia, when a patient is paralyzed with muscle relaxants but not enough general anesthetic or analgesic to prevent consciousness or, more importantly, the sensation of pain and the recall of events. ...

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. The pharynx (plural: pharynges) is the part of the neck and throat situated immediately posterior to the mouth and nasal cavity, and cranial to the esophagus, larynx, and trachea. ... An endotracheal tube (ETT) is used in anaesthesia, intensive care and emergency medicine for airway management and mechanical ventilation. ...

General anaesthesia

Premedication

Anaesthetists 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. For other uses of painkiller, see painkiller (disambiguation) An analgesic (colloquially known as painkiller) is any member of the diverse group of drugs used to relieve pain. ...

Pre-med's are not routinely used in modern anaesthesia, but are still common.

Induction

The general anaesthetic is administered in either the operating theatre itself or a special ante-room.

General anaesthesia can be induced by intravenous (IV) injection, or breathing a volatile anaesthetic through a facemask (inhalational induction). Onset of anaesthesia 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 anaesthesia (see below), and thus reduces complications related to induction of anaesthesia. An inhaltional induction may be chosen by the anaesthetist 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. An intravenous drip in a hospital Intravenous therapy or IV therapy is the administration of liquid substances directly into a vein. ... The volatile anaesthetics are a class of general anaesthetic drugs. ... Propofol is an intravenous anesthetic agent used for the induction of general anesthesia in adult patients and pediatric patients older than 3 years of age; maintenance of general anesthesia in adult patients and pediatric patients older than 2 months of age; and intensive care unit (ICU) sedation for intubated, mechanically... Sodium thiopental also called Sodium Pentothal (a trademark of Abbott Laboratories), thiopental, thiopentone sodium, or trapanal is a rapid-onset, short-acting barbiturate general anesthetic. ... Etomidate is a short acting intravenous anaesthetic agent used for the induction of general anaesthesia and for sedation for short procedures such as reduction of dislocated joints and cardioversion. ... For the collaborative acoustic project, see Katamine. ...

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 anaesthesia for the required duration (usually the duration of surgery), anaesthesia must be maintained. Usually this is acheived by allowing the patient to breathe a carefully controlled mixture of oxygen and a volatile anaesthetic 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 anaethetic is discontinued. Recovery of consciousness occurs when the concentration of anaesthetic in the brain drops below a certain level (usually within 1 to 30 minutes depending upon the duration of surgery). The volatile anaesthetics are a class of general anaesthetic drugs. ...

In the 1990s a novel method of maintaining anaesthesia was developed in Glasgow, UK. Called Total IntraVenous Anaesthesia (TIVA), this involves using a computer controlled syringe driver (pump) to infuse propofol throughout the duration of surgery, removing the need for a volatile anaesthetic. Purported advantages include faster recovery from anaesthesia, reduced incidence of post-operative nausea and vomiting, and abscence of a trigger for malignant hyperthermia. Malignant hyperthermia (MH or MHS for malignant hyperthermia syndrome, or malignant hyperpyrexia due to anesthesia) is a life-threatening condition resulting from a genetic sensitivity of skeletal muscles to volatile anaesthetics and depolarizing neuromuscular blocking drugs that occurs during or after anaesthesia. ...

Paralysis

Inducing paralysis with a neuromuscular blocker is an integral part of modern anaesthesia. 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. It has been suggested that Paralytic agent be merged into this article or section. ... Strychnos toxifera by Koehler 1887 This page is about the plant. ...

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. Intraoperative X-Ray of a Humerus fixated by Kirschner wires Surgery (from the Greek meaning hand work) is the medical specialty that treats diseases or injuries by operative manual and instrumental treatment. ... By the broadest definition, a body cavity is any fluid filled space in a multicellular organism. ... The abdomen is a part of the body. ... Diagram of a tsetse fly, showing the head, thorax and abdomen The thorax is a division of an animals body that lies between the head and the abdomen. ... Intubation being practiced on a dummy (conventional technique using a laryngoscope) In medicine, intubation is the placement of a tube into an external or internal orifice of the body. ...

Acetylcholine, the natural neurotransmitter substance at the neuromuscular junction, causes muscles to contract when released from nerve endings. Muscle relaxants work by preventing acetylcholine from attaching to its receptor. Chemical structure of D-Aspartic Acid, a common Amino Acid neurotransmitter. ... A neuromuscular junction is the junction of the axon terminal of a motoneuron with the motor end plate, the highly-excitable region of muscle fiber plasma membrane responsible for initiation of action potentials across the muscles surface. ...

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. Respiration is the process by which an organism obtains energy by reacting oxygen with glucose to give water, carbon dioxide and ATP (energy). ... In the anatomy of mammals, the diaphragm is a shelf of muscle extending across the bottom of the ribcage. ... Intercostal can refer to: Intercostal muscle Highest intercostal vein Intercostal arteries This is a disambiguation page: a list of articles associated with the same title. ... The pharynx (plural pharynx), or voicebox, is an organ in the neck of mammals involved in protection of the trachea and sound production. ... The airways are those parts of the respiratory system through which air flows, to get from the external environment to the alveoli. ... An endotracheal tube (ETT) is used in anaesthesia, intensive care and emergency medicine for airway management and mechanical ventilation. ...

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. Nerves (yellow) Nerves redirects here. ... For alternate meanings see skin (disambiguation). ...

The effects of muscle relaxants are commonly reversed at the termination of surgery by anticholinesterase drugs. A cholinesterase inhibitor or anticholinesterase is a chemical that inhibits a cholinesterase enzyme from breaking down acetylcholine, so increasing both the level and duration of action of the neurotransmitter acetylcholine. ...

Examples of skeletal muscle relaxants in use today are pancuronium, rocuronium, vecuronium, atracurium, mivacurium, and succinylcholine. Pancuronium bromide is a chemical compound, used in medicine with the brand name Pavulon® (Organon Pharmaceuticals). ... Rocuronium is a non-depolarizing (that is, it does not cause initial stimulation of muscles before weakening them) neuromuscular blocker used in modern anaesthesia, to aid and enable endotracheal intubation, which is often necessary to assist in the controlled ventilation of unconscious patients during surgery and sometimes in intensive care. ... Vecuronium Bromide is a muscle relaxant in the category of non depolarising neuromuscular blocking agents. ... Atracurium is a neuromuscular-blocking drug or muscle relaxant in the category non-depolarising neuromuscular blocking agents, used in anaesthesia to facilitate endotracheal intubation and to provide skeletal muscle relaxation during surgery or mechanical ventilation. ... Mivacurium is a bisbenzylisoquinolinium based neuromuscular blocker or muscle relaxant. ... Suxamethonium chloride (also known as succinylcholine, or scoline) is a white crystalline substance, it is odourless and highly soluble in water. ...

Airway management

With the loss of consciousness caused by general anaesthesia, 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. An opioid is any agent that binds to opioid receptors, found principally in the central nervous system and gastrointestinal tract. ... In medicine, a muscle relaxant is a drug that causes skeletal muscle contraction to cease. ... Bag valve mask In medicine, mechanical ventilation is a method to assist or replace spontaneous breathing. ... An endotracheal tube (ETT) is used in anaesthesia, intensive care and emergency medicine for airway management and mechanical ventilation. ... Intubation being practiced on a dummy (conventional technique using a laryngoscope). ... The laryngeal mask airway (LMA) is used in anaesthesia and in emergency medicine for airway management. ...

Monitoring

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

1. Continuous Electrocardiography (ECG): The placement of electrodes which monitor heart rate and rhythm. This may also help the anaesthetist to identify early signs of heart ischemia. In medicine, ischemia (Greek ισχαιμία, isch- is restriction, hema or haema is blood) is a restriction in blood supply, generally due to factors in the blood vessels, with resultant damage or dysfunction of tissue. ...

2. Continuous pulse oximetry (SpO2): The placement of this device (usually on one of the fingers) allows for early detection of a fall in a patient's hemoglobin saturation with oxygen (hypoxemia). Pulse oximetry is a non-invasive method which allows health care providers to monitor the oxygenation of a patients blood. ... 3-dimensional structure of hemoglobin. ... Hypoxia is a pathological condition in which the body as a whole (generalised hypoxia) or region of the body (tissue hypoxia) is deprived of adequate oxygen supply. ...

3. Blood Pressure Monitoring (NIBP or IBP): There are two methods of measuring the patient's blood pressure. The first, and most common, is called non-invasive blood pressure (NIBP) monitoring. This involves placing a blood pressure cuff around the patient's arm, forearm or leg. A blood pressure machine takes blood pressure readings at regular, preset intervals throughout the surgery. The second method is called invasive blood pressure (IBP) monitoring. This method is reserved for patients with significant heart or lung disease, the critically ill, major surgery such as cardiac or transplant surgery, or when large blood losses are expected. The invasive blood pressure monitoring technique involves placing a special type of plastic cannula in the patient's artery - usually at the wrist or in the groin.

4. Agent concentration measurement - Common anaesthetic machines have meters to measure the percent of inhalational anaesthetic agent used (e.g. sevoflurane, isoflurane, desflurane, halothane etc). In chemistry, concentration is the measure of how much of a given substance there is mixed with another substance. ... An anaesthetic machine The anaesthetic machine (or anesthesia machine in America) is used by anaesthetists to support the administration of anaesthesia. ... Inhalational anaesthetics are gases or vapours possessing anaesthetic qualities. ... Sevoflurane (2, 2, 2-trifluoro-1-(trifluoromethyl) ethyl ether), also called fluoromethyl, is a halogenated ether used for induction and maintenance of general anesthesia. ... Structural formula of isoflurane Isoflurane (1-chloro-2,2,2-trifluoroethyl difluoromethyl ether) is a halogenated ether used for inhalation anesthesia. ... Desflurane is a highly flourinated ether used for maintenance of general anaesthesia. ... Structural formula of halothane Halothane vapour is an inhalational general anaesthetic. ...

5. Low oxygen alarm - Almost all circuits have a backup alarm in case the oxygen delivery to the patient becomes compromised. This warns if the fraction of inspired oxygen drops lower than room air (21%) and allows the anaesthetist to take immediate remedial action. General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance transparent (gas) very pale blue (liquid) Atomic mass 15. ... An anesthesiologist (American English), or anaesthetist (British English), is a medical doctor trained to administer Australia, for example, training is overseen by the United States, anesthesiologists are medical doctors (MD). ...

6. Circuit disconnect alarm - indicates failure of circuit to achieve a given pressure during mechanical ventilation. Bag valve mask In medicine, mechanical ventilation is a method to assist or replace spontaneous breathing. ...

7. Carbon dioxide measurement (capnography)- measures the amount of carbon dioxide expired by the patient's lungs. It allows the anaesthetist to assess the adequacy of ventilation Carbon dioxide is an atmospheric gas comprised of one carbon and two oxygen atoms. ... Capnography is the indirect monitoring of carbon dioxide (CO2) concentrations in a patients blood. ... Ventilation good and very bad Ventilation is air circulation of air, typically between a room, a tunnel, etc. ...

8. Temperature measurement to discern hypothermia or fever, and to aid early detection of malignant hyperthermia. Hypothermia is a medical condition in which the victims core body temperature has dropped to significantly below normal and normal metabolism begins to be impaired. ... A medical/clinical thermometer showing the temperature of 38. ... Malignant hyperthermia (MH or MHS for malignant hyperthermia syndrome, or malignant hyperpyrexia due to anesthesia) is a life-threatening condition resulting from a genetic sensitivity of skeletal muscles to volatile anaesthetics and depolarizing neuromuscular blocking drugs that occurs during or after anaesthesia. ...

9. EEG or other system to verify depth of anaesthesia may also be used. This reduces the likelihood that a patient will be mentally awake, although unable to move because of the paralytic agents. It also reduces the likelihood of a patient receiving significantly more amnesic drugs than actually necessary to do the job.

Stages of anaesthesia

Stage 1

Stage 1 anaesthesia, 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. Paitents can carry on a conversation at the time.

Stage 2

Stage 2 anaesthesia, also known as the "excitement stage," is the period following loss of consciousness and marked by excited and delerious activity. During this stage, respirations and heart rate may become irregular. In addition, there may be uncontrolled movements, vomiting, breath holding, and pupillary dilation. 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 anaesthesia, 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 anaesthesia are the patient's respiratory and cardiovascular response to stimulation.

Stage 4

Stage 4 anaesthesia, 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 anaesthesia concludes with a management plan for postoperative pain relief.

This may be in the form of regional analgesia, oral or parenteral medication. Regional analgesia blocks passage of pain impulses through a nerve by depositing an analgesic drug close to the nerve trunk, cutting off sensory innervation to the region it supplies. ... In pharmacology and toxicology, a route of administration is the path by which a drug, fluid, poison or other substance is brought into contact with the body 1. ...

Minor surgical procedures are amenable to oral pain relief medications such as paracetamol and NSAIDS such as ibuprofen. Paracetamol (INN) (IPA: ) or acetaminophen (USAN) is a common analgesic and antipyretic drug that is used for the relief of fever, headaches, and other minor aches and pains. ... Wikipedia does not yet have an article with this exact name. ... Ibuprofen (INN) (IPA: ) is a non-steroidal anti-inflammatory drug (NSAID) widely marketed under various trademarks including Act-3, Advil, Brufen, Motrin, Nuprin, and Nurofen. ...

Moderate levels of pain require the addition of mild opiates such as codeine. An opioid is any agent that binds to opioid receptors found principally in the central nervous system and gastrointestinal tract. ... This article is about the drug. ...

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. Morphine (INN) (IPA: ) is an extremely powerful opiate analgesic drug and is the principal active agent in opium. ...

Mortality rates

Overall, the mortality rate for general anaesthesia is about five deaths per million anaesthetic administrations.^[1]

Death during anaesthesia is most commonly related to surgical factors or pre-existing medical conditions. These include major haemorrhage, sepsis, and organ failure (eg. heart, lungs, kidneys, liver). Hemorrhage (alternate spelling is Haemorrhage) is the medical term meaning bleeding. ... Sepsis (in Greek Σήψις, putrefaction) is a serious medical condition, resulting from the immune response to a severe infection. ...

Common causes of death directly related to anaesthesia include:

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

Footnotes

1. ^ Henry Rosenberg. Mortality Associated with Anesthesia. ExpertPages.com. Retrieved on 2006-07-11.

2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... July 11 is the 192nd day (193rd in leap years) of the year in the Gregorian Calendar, with 173 days remaining. ...

External links

• Chloroform: The molecular lifesaverAn article at Oxford University providing interesting facts about chloroform.

• Australian & New Zealand College of Anaesthetists Monitoring Standard

• Royal College of Anaesthetists Patient Information page