General anaesthesia eliminates consciousness and pain perception in the entire body. It is a temporary state similar to deep sleep that is produced by a combination of substances (sleep-inducing agents, analgesics, drugs that relax muscles and affect the autonomic nervous system). These substances are either injected into a vein (IV) or inhaled. The patient does not feel or hear anything from his or her surroundings during the procedure.
Anaesthesia is normally induced by injecting a medication into the IV infusion, in adults only in exceptional cases by inhalation of an anaesthetic gas. A mask may be placed over the face in order to provide more oxygen prior to inducing sleep.
Once the patient has lost consciousness, the breathing is assisted using the face mask. This method is continued during short procedures of up to 15 minutes’ duration.
For longer procedures, the airways are secured by by placing a tube into the trachea (intubation) or the pharynx (laryngeal mask).
In longer procedures, mechanical ventilation is usually used; this is facilitated by intubation, as it isolates the airway from the digestive tract and thus prevents saliva, gastric juice, or gastric contents from entering the lungs (aspiration).
Modern, short-acting drugs ensure that the recovery phase is brief and without unpleasant side effects.
Respiration is monitored continuously (pulse oximetry, C02 measurement) and supported via the face or laryngeal mask or a tracheal tube.
The circulation is also monitored continuously (ECG, blood pressure, pulse oximetry), and fluids and drugs are administered as needed. Patients routinely receive small amounts of saline solution via an IV infusion.
The anaesthetic depth is also monitored continuously using a modern method (bispectral index, BIS).