page_title: Anesthesia
section_title: General anesthesia
hierarchical_section_title: Anesthesia / Techniques / General anesthesia
caption_attribution_description: English: Syringes prepared with medications that are expected to be used during an operation under general anesthesia maintained by sevoflurane gas: Propofol, a hypnotic Ephedrine, in case of hypotension Fentanyl, for analgesia Atracurium, for neuromuscular block Glycopyrronium bromide (here under trade name Robinul), reducing secretions
context_page_description: Anesthesia or anaesthesia is a state of controlled, temporary loss of sensation or awareness that is induced for medical purposes. It may include some or all of analgesia, paralysis, amnesia, and unconsciousness. A patient under the effects of anesthetic drugs is referred to as being anesthetized.
  Anesthesia enables the painless performance of medical procedures that would otherwise cause severe or intolerable pain to an unanesthetized patient, or would otherwise be technically unfeasible. Three broad categories of anesthesia exist:
  General anesthesia suppresses central nervous system activity and results in unconsciousness and total lack of sensation, using either injected or inhaled drugs.
  Sedation suppresses the central nervous system to a lesser degree, inhibiting both anxiety and creation of long-term memories without resulting in unconsciousness.
  Regional and local anesthesia, which blocks transmission of nerve impulses from a specific part of the body. Depending on the situation, this may be used either on its own, or in combination with general anesthesia or sedation.
context_section_description: Anesthesia is a combination of the endpoints (discussed above) that are reached by drugs acting on different but overlapping sites in the central nervous system.  General anesthesia (as opposed to sedation or regional anesthesia) has three main goals: lack of movement (paralysis), unconsciousness, and blunting of the stress response.  In the early days of anesthesia, anesthetics could reliably achieve the first two, allowing surgeons to perform necessary procedures, but many patients died because the extremes of blood pressure and pulse caused by the surgical insult were ultimately harmful.  Eventually, the need for blunting of the surgical stress response was identified by Harvey Cushing, who injected local anesthetic prior to hernia repairs. This led to the development of other drugs that could blunt the response leading to lower surgical mortality rates.
  The most common approach to reach the endpoints of general anesthesia is through the use of inhaled general anesthetics.  Each anesthetic has its own potency which is correlated to its solubility in oil. This relationship exists because the drugs bind directly to cavities in proteins of the central nervous system, although several theories of general anesthetic action have been described. Inhalational anesthetics are thought to exact their effects on different parts of the central nervous system.  For instance, the immobilizing effect of inhaled anesthetics results from an effect on the spinal cord whereas sedation, hypnosis and amnesia involve sites in the brain.  The potency of an inhalational anesthetic is quantified by its minimum alveolar concentration or MAC.  The MAC is the percentage dose of anesthetic that will prevent a response to painful stimulus in 50% of subjects.  The higher the MAC, generally, the less potent the anesthetic.
  The ideal anesthetic drug would provide hypnosis, amnesia, analgesia, and muscle relaxation without undesirable changes in blood pressure, pulse or breathing.  In the 1930s, physicians started to augment inhaled general anesthetics with intravenous general anesthetics.  The drugs used in combination offered a better risk profile to the person under anesthesia and a quicker recovery.  A combination of drugs was later shown to result in lower odds of dying in the first 7 days after anesthetic. For instance, propofol (injection) might be used to start the anesthetic, fentanyl (injection) used to blunt the stress response, midazolam (injection) given to ensure amnesia and sevoflurane (inhaled) during the procedure to maintain the effects.  More recently, several intravenous drugs have been developed which, if desired, allow inhaled general anesthetics to be avoided completely.
caption: Syringes prepared with medications that are expected to be used during an operation under general anesthesia maintained by sevoflurane gas: 
  - Propofol, an hypnotic 
  - Ephedrine, in case of hypotension 
  - Fentanyl, for analgesia 
  - Atracurium, for neuromuscular blockade 
  - Glycopyrronium bromide (here under trade name "Robinul"), reducing secretions
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