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.