An anaesthetic is started (induced) by either injecting an anaesthetic drug or allowing the patient to breathe anaesthetic gas/vapour.  This usually takes between 1 and 3 minutes. Once a patient is asleep, the anaesthetic is continued (maintained) by using a continuous infusion of an anaesthetic drug into the vein or by ventilating the patient with the anaesthetic gas/vapour.  The anaesthetic agent that is used for such an infusion is most commonly the drug propofol (diprivan).  This is close to an ideal drug as it has a short duration of action and does not accumulate in the patient.  Once the infusion is terminated it will take between 5 – 15 minutes for the patient to awaken.  Likewise the most commonly used anaesthetic vapours are sevoflurane and desflurane.  These agents also have a short duration of action and once they are ceased, the patient will awaken within 10 minutes.

These agents can be administered for many hours without any harmful side effects.  When the surgeon is nearing the end of the procedure, the anaesthetist will start preparing for reversal of the anaesthetic.  When the procedure is finished, the anaesthetic agents are stopped and the patient is allowed to awaken.  In this way, there is no danger of the patient waking before the procedure is completed.

However, a patient may have recall of waking with a tube in their mouth or throat.  This is a normal event as it often not possible to remove the breathing device (endotracheal tube) before a patient is awake as they may obstruct their airway and be unable to breathe.

With the induction of anaesthesia, most patients lose the ability to maintain an open airway and almost invariably stop breathing.  If left unattended, a patient will desaturate (falling oxygen levels in the blood) within a 1 – 3 minutes.  The primary responsibility of the anaesthetist is to prevent this happening and to maintain adequate ventilation for the patient.  There are various manoeuvres the anaesthetist will use and this frequently involves using an airway device such as a laryngeal mask or an endotracheal tube.

Examining a patients airway carefully before embarking on administering an anaesthetic is essential to preparing for problems that may occur.  Some patients have difficult airways and may be either difficult to ventilate or intubate.  There are numerous special devices available to facilitate this process when difficulties are encountered.  However as it takes less than 3 minutes for a non-breathing patient to desaturate, the anaesthetist has to be prepared and ready for this event.

Examination of the teeth is important as the insertion of the airway devices into the mouth can damage loose teeth/caps/crowns.  If the anaesthetist is aware of the position of these teeth, they can usually adjust their technique to avoid causing any damage.