Ans. C: Nitrous oxideGeneral anaesthesia can be induced by intravenous (IV) injection, or breathing a volatile anaesthetic through a facemask (inhalational induction).Onset of anaesthesia is faster with IV injection than with inhalation, taking about 10-20 seconds to induce total unconsciousness.This has the advantage of avoiding the excitatory phase of anaesthesia, and thus reduces complications related to induction of anaesthesia.An inhalational induction may be chosen by the anesthesiologist where IV access is difficult to obtain, where difficulty maintaining the airway is anticipated, or due to patient preference (e.g. children).Commonly used IV induction agents include propofol, sodium thiopental, etomidate, and ketamine.The most commonly-used agent for inhalational induction is sevoflurane because it causes less irritation than other inhaled gasesIn order to prolong anaesthesia for the required duration (usually the duration of surgery), anaesthesia must be maintained. Usually this is achieved by allowing the patient to breathe a carefully controlled mixture of oxygen, nitrous oxide, and a volatile anaesthetic agent or by having a carefully controlled infusion of medication, usually propofol, through an IV.Induction Characteristics & Dosage Requirements for Currently AvailableSedative & Hypnotic DrugsDrug NameInduction Dose (mg/kg)Onset (sec)Duration (min)Thiopental3-6<305-10Methohexital1-3<305-10Propofol1.5-2.515-455-10Midazolam0.2-0,430-9010-30Diazepam0.3-0.645-9015-30Lorazepam0.03-0.0660-12060-120Etomidate0.2-0.33-123-12Ketamine1-210-2010-20