When a patient goes for an operation, he may be placed under 3 types of anaesthesia.
Local anaesthesia: the relevant part of the body is numbed.
Regional anaesthesia: numbs a larger area of the body through administering an anaesthetic drug to a cluster of nerves.
General anaesthesia (GA) refers to a state of unconsciousness (like sleep) and the lack of awareness or sensation.
GA can be induced by intravenous (IV) injection, or by breathing a volatile (a liquid that evaporates easily at normal temperatures and pressures) anaesthetic through a face mask (inhalational induction).
The onset of anaesthesia is faster with IV injection than with inhalation, taking about 10-20 seconds to induce total unconsciousness.
The IV inductions agents work in 5 to 10 minutes. Hence, anaesthesia must be prolonged or maintained for the whole process of surgery.