General anaesthesia is a state of nonresponsiveness to surgical stimuli (pain) of the whole body accompanied by a temporary interruption of conscious processing of thoughts. General anaesthesia is mostly induced by intravenous application of anaesthetic drugs and is thereafter maintained either by a continuous infusion or by the introduction of a volatile anaesthetic to the air that the patient breathes. Since the ability to maintain spontaneous respiration can be impaired during general anaesthesia, an artificial airway device is often introduced in order to maintain airway patency and to serve as a connection between the anaesthesia machine providing some degree of artificial ventilatory (breathing) support and the patient’s lung. At the end of the surgical procedure the delivery of anaesthetic agents is interrupted and the patient gradually regains consciousness.
Regional anaesthesia involves procedures that interrupt the conduction of painful stimuli only from one part or region of the body. Regarding the level at which the pain conduction pathway is interrupted regional anaesthesia procedures are divided in two large groups:
Neuraxial anaesthesia – includes epidural and subarachnoid (spinal) anaesthesia, procedures in which anaesthetics are introduced into the spinal canal and block the propagation of impulses in pain pathways along the spinal cord and nerve roots emerging from it.
Peripheral nerve blocks – anaesthetics are injected along peripheral nerve bundles or individual nerves and interrupt their conduction.
Regional anaesthesia regularly involves a certain degree of motoric blockade resulting in impaired mobility of one of the extremities or of the entire lower body in the case of neuraxial anaesthesia.
Sympathetic fibre blockade during regional anaesthesia is responsible for the vasodilatation resulting in a feeling of warmth some patients experience due to blood pooling in the involved area.
Regional anaesthesia procedures can involve the placement of catheters which enable the continued postoperative delivery of drugs providing long lasting analgesia.
Local anaesthesia – local anaesthetics are infiltrated directly into the operative site and tissue immediately surrounding it in order to render it insensitive. Usually this form of anaesthesia is performed by the surgeon.
Sedation – is a state of diminished consciousness achieved by application of drugs that decrease the activity of the central nervous system and in higher doses are used to produce general anaesthesia. The level of sedation is usually adjusted according to patient anxiety and the discomfort associated with the surgical or diagnostic procedure being performed. Usually the patient can easily be aroused and verbal contact established. Airway patency and spontaneous respirations are also preserved at all but the deepest levels of sedation.