Before a planned general anaesthesic, the patient will have a period of fasting
The purpose of fasting is to make sure they have an empty stomach, to reduce the risk of the stomach contents refluxing into the oropharynx, then being aspirated into the trachea
Gastric contents in the lungs creates an aggressive inflammatory response, causing pneumonitis (
The risk of aspiration is highest before and during intubation, and when they are extubated
Once the endotracheal tube is correctly fitted, the airway is blocked and protected from aspiration
Aspiration pneumonitis and pneumonia are major causes of morbidity and mortality in anaesthetics, although with planned procedures they are very rare
Fasting for an operation typically involves:
6 hours of no food or feeds before the operation
2 hours of no clear fluids (fully ‘nil by mouth’)
In emergency situations the patient may not be fasted
Preoxygenation
Before being put under a general anaesthetic, the patient will have a period of several minutes where they breathe 100% oxygen
This gives them a reserve of oxygen for the period between when they lose consciousness and are successfully intubated and ventilated
Pre-medication
Medications are given before the patient is put under a general anaesthetic to relax them, reduce anxiety, reduce pain and make intubation easier
These may include:
Benzodiazepines (e.g., midazolam) to relax the muscles and reduce anxiety (also causes amnesia)
Opiates (e.g., fentanyl or alfentanyl) to reduce pain and reduce the hypertensive response to the laryngoscope
Triad of general anaesthesia
Hypnosis
Hypnotic agents are used to make the patient unconscious
They can be either given intravenously e.g. propofol or by inhalation e.g. sevoflurane