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Encyclopedia > General anesthesia

In modern medical practice, general anaesthesia is a state of total unconsciousness resulting from 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 anesthesiologist selects the optimal technique for any given patient and procedure. Unconsciousness is the absence of consciousness. ... Amnesia (or amnaesia in Commonwealth English) 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. ... An anesthesiologist (American English), or anaesthetist (British English), is a medical doctor trained to administer anesthesia. ...


General anaesthesia is a complex procedure involving:

Contents

A general anaesthetic drug is an anaesthetic (or anesthetic AE) drug that brings about a reversible loss of consciousness. ... A continuing function that uses systematic collection of data on specified indicators to provide management and the main stakeholders of an ongoing development intervention with indications of the extent of progress and achievement of objectives and progress in the use of allocated funds ... 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

Before surgery, the anaesthesiologist or nurse anaesthetist will do a preanaesthetic evaluation to determine which drugs (including dosages), additional invasive monitors and/or analgesic therapies he or she will use. In this interview the anaesthesiologist will ask for the patient's age, weight, medical history, current medications, previous anesthetics, and other factors relevant to administering anesthesia. Often, the patient will fill in this information on a separate form when he comes to the hospital for his pre-operative evaluation. Depending on the existing medical conditions reported, the anaesthesia provider will review this information with the patient either during his pre-operative evaluation or on the day of his surgery. Hospital staff will take note of the last meal ingested (including gum chewed!), and any fluids consumed, and a history of acid-indigestion or regurgitation is also sought.


It is extremely important that the patient answer these questions truthfully so that the anaesthesia provider can select the proper anaesthetic. For instance, a heavy drinker or drug user who does not disclose their chemical uses could be undermedicated, which could then lead to awareness under anaesthesia or dangerously high blood pressure.


An important aspect of this assessment is that of the patients airway, involving inspection of the mouth opening and visualisation of the soft tissues of the pharynx (tongue, uvular, soft palate and tonsils) - graded by the "Mallampati test". The condition of teeth and location of dental crowns and caps are checked, as well as the ability to adopt the ideal position for intubation (known as "sniffing the morning air"), tested by observing neck flexibility and head extension. If an endotracheal tube is indicated and airway management is deemed difficult, then alternative placement methods such as fiberoptic intubation may be used. An endotracheal tube (ETT) is used in anaesthesia, intensive care and emergency medicine for airway management and mechanical ventilation. ...


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 anesthesia provider 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 percent saturation of oxygen which warns the anaesthesia provider when the patient is hypoxemic, low blood levels of oxygen. 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. ...


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 radial or femoral artery.


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. ... Anaesthetists use anaesthetic machines 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. ... 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 Chalcogens Group, Period, Block 16, 2, p Appearance colorless 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. ventilation balloon In medicine, mechanical ventilation is a method to assist or replace spontaneous breathing. ...


7. Carbon dioxide measurement (capnography) 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. ...


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. ... See Fever for the Kylie Minogue album; Fever is also a song by Otis Blackwell. ... Malignant hyperthermia (MH or MHS for malignant hyperthermia syndrome) 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. ...


Administration of General Anaesthetic

Anaesthetists may give a pre-medication ('pre-med') by injection or tablets a couple of hours before surgery to induce drowsiness and relaxation. The general anaesthetic will then be administered in either the operating theatre itself or a special ante-room. General anaesthetic can be given by injection, or inhaled by mask, or by both. The needle works quicker than the mask, it taking ten seconds or less to induce total unconsciousness. The mask is used more for children, but is sometimes used on adults along with the needle.


Muscle Relaxation

Muscle relaxation with skeletal muscle relaxants is an integral part of modern anaesthesia. The first drug used for this purpose was curare, introduced in the 1940's and now superseded with drugs with fewer side effects, and generally shorter duration. In medicine, a muscle relaxant is a drug that causes skeletal muscle contraction to cease. ... Strychnos toxifera by Koehler 1887 Curare refers to the alkaloid containing substance obtained from one of several plants, the purified products of which are used as skeletal muscle relaxants. ...


Muscle relaxation, also known as neuro-muscular blockade, allows surgery within major body cavities, eg. abdomen and thorax without the need for very deep planes of anesthesia, and is also used to facilitate endotracheal intubation. A typical modern surgery operation Surgery (from the Greek cheirourgia 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. ... In anatomy, the abdomen is a part of the body; in humans, it is the region between the thorax and the pelvis. ... 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. ...


Muscle relaxation causes paralysis of the muscles of respiration, ie. the diaphragm and intercostal muscles of the chest, and therefore requires that some form of artificial respiration, usually by connection of the patient to a mechanical ventilator. The muscles of the larynx are also paralysed so that the airway usually needs to be protected by means of an endotracheal tube. Paralysis is the complete loss of muscle function for one or more muscle groups. ... Respiration is the process of exchanging oxygen and carbon dioxide between an organism and its external environment (breathing). ... A diaphragm is some sort of separating membrane. ... The larynx (plural larynges), or voicebox, is an organ in the neck of mammals involved in protection of the trachea and sound production. ...


Muscle relaxants work by antagonising the natural neurotransmitter substance acetylcholine at the neuromuscular junction. Thus, nerve impulses which would normally cause muscles to contract are prevented from reaching their supplied muscles, causing them to relax. Neurotransmitters are chemicals that are used to relay, amplify and modulate electrical signals between a neuron and another cell. ... The chemical compound acetylcholine, often abbreviated as ACh, was the first neurotransmitter to be identified. ... 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. ... A. A schematic view of an idealized action potential illustrates its various phases as the action potential passes a point on a cell membrane. ...


Monitoring of muscle relaxation 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. Nerves (yellow)    Nerves redirects here. ... Model of the layers of human skin In zootomy and dermatology, skin is an organ of the integumentary system composed of a layer of tissues that protect underlying muscles and organs. ... 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) muscle relaxant used in modern anaesthesia, to aid and enable endotracheal intubation, and controlled ventilation of unconscious patients during surgery, or sometimes in intensive care. ... Vecuronium Bromide is a muscle relaxant in the category of non depolarising neuromuscular blocking agents. ... 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 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. 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. ... ventilation balloon 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 sometimes in emergency medicine for airway management. ...


External links

  • Australian & New Zealand College of Anaesthetists Monitoring Standard

  Results from FactBites:
 
Risks of General Anesthesia - Liposuction.com (920 words)
Local Anesthesia is defined as the infiltration of local anesthesia directly into the tissues targeted for surgery, with or without outpatient oral medication for analgesia, sedation, or to reduce anxiety.
Systemic Anesthesia is defined as any anesthetic technique, with or without local anesthesia, that has a significant risk and potential for impairing the protective airway reflexes or for suppression of the respiratory drive.
General anesthesia and IV sedation-analgesia are similar in terms of both risks and requirements for monitoring patients.
General anaesthesia - Wikipedia, the free encyclopedia (1131 words)
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 percent saturation of oxygen which warns the anaesthesia provider when the patient is hypoxemic, low blood levels of oxygen.
General anaesthetic can be given by injection, or inhaled by mask, or by both.
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.
  More results at FactBites »

 
 

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