A general anaesthetic drug is an anaesthetic (or anesthetic AE) drug that brings about a reversible loss of consciousness. These drugs are generally administered by an anaesthetist(CE) (or anesthesiologistAE) in order to induce or maintain general anaesthesiato facilitate surgery.
Drugs given to induce or maintain general anaesthesia are either given as:
- Gases or vapors (inhalation anaesthetics)
- Injections (intravenous anaesthetics).
Most commonly these two forms are combined, with an injection given to induce anaesthesia and a gas used to maintain it, although it is possible to deliver anaesthesia solely by inhalation or injection.
Inhalational anaesthetic substances are either volatileliquidsor gasesand are usually delivered using an anaesthesia machine. An anaesthesia machine allows composing a mixture of oxygen, anaesthetics and ambient air, delivering it to the patient and monitoring patient and machine parameters. Liquid anaesthetics are vaporized in the machine.
Many compounds have been used for inhalation anaesthesia, but only a few are still in widespread use. Desfluraneand sevofluraneare the most widely used volatile anaestheticstoday. They are often combined with nitrous oxide. Older, less popular, volatile anesthetics, include isoflurane(used commonly in veterinary medicine), halothane, enflurane, and methoxyflurane. Researchers are also actively exploring the use of xenonas an anaesthetic.
Injection anaesthetics are used for induction and maintenance of a state of unconsciousness. Anaesthetists prefer to use intravenous injectionsas they are faster, generally less painful and more reliable than intramuscularor subcutaneous injections. Among the most widely used drugs are:
- Barbituratessuch as methohexitaland thiopentone/thiopental
- Benzodiazepinessuch as midazolamand diazepam(commonly known as Valium)
- Ketamine(commonly known as the street drug Special K, and used as a date rape drug)
Mechanism of action
Researchers agree that ion channels are the ultimate site of action of general anaesthetics, and are now determining the exact molecular mechanisms. However, the sites of action of general anaesthetics proved difficult to identify until the last decade. The wide variation in structure, ranging from complex steroidsto the inert monatomic gas xenon, led to several now outdated theories of anaesthetic action.
It is now known that general anaesthetics act on the central nervous systemby modifying the electrical activity of neurons at a molecular level by modifying the function of ion channels. This may occur by anaesthetic molecules binding directly to ion channels or by their disrupting the function of molecules that maintain ion channels.
Scientists have cloned forms of receptors in the past decade, adding greatly to knowledge of the proteinsinvolved in neuronal excitability. These include:
- Voltage-gated ion channels, such as sodium, potassium, and calcium channels
- Ligand-gated ion channelsuperfamily
- G protein-coupled receptorsuperfamily
- Local anesthesia
- Mechanical ventilation
- Intraoperative awarenessde:Narkose
Categories: Pharmacology| Anesthesia
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It uses material from the http://en.wikipedia.org/wiki/General+anaesthetic Wikipedia article General anaesthetic.