Induction
Induction of general anaesthesia is usually conducted in a medical facility, most commonly in an operating room. However, general anaesthesia may also be conducted in many other locations, such as an endoscopy suite, radiology or cardiology department, emergency department, ambulance, or at the site of a disaster where extrication of the patient may be impossible or impractical.
Anaesthetic agents may be administered by various routes, including inhalation, injection (intravenous, intramuscular or subcutaneous), oral, and rectal. After administration by one or more of these routes, the agents gain access to the blood. Once in the circulatory system, they are transported to their biochemical sites of action in the central and autonomic nervous systems, where they exert their pharmacologic effects.
Most general anaesthetics today are induced either with a needle, by intravenous injection, or by breathing a volatile anaesthetic through an anaesthetic circuit (inhalational induction). Onset of anaesthesia is faster with intravenous 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 above), and thus reduces complications related to induction of anaesthesia. Commonly used intravenous induction agents include propofol, sodium thiopental, etomidate, and ketamine. An inhalational induction may be chosen by the anaesthesiologist where intravenous access is difficult to obtain, where difficulty maintaining the airway is anticipated, or due to patient preference (e.g., children). Sevoflurane is currently the most commonly used agent for inhalational induction, because it is less irritating to the tracheobronchial tree than other volatile anaesthetic agents.
Read more about this topic: General Anaesthesia
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