Anaesthesia is a pharmacologically induced reversible state of amnesia, analgesia, loss of responsiveness, loss of skeletal muscle reflexes and decreased stress response.

An anaesthetised patient can be thought of as being in a controlled and reversible state of unconsciousness. Anaesthesia enables a patient to tolerate surgical procedures that would otherwise inflict unbearable pain, potentiate extreme physiologic responses and result in unpleasant memories.

There are several forms of anaesthesia.

General Anaesthesia

  • General anaesthesia: “Drug-induced loss of consciousness during which patients are not rousable, even by painful stimulation.”


  • Deep sedation / analgesia: “Drug-induced depression of consciousness during which patients cannot be easily aroused but respond purposefully following repeated or painful stimulation.”
  • Moderate sedation / analgesia or conscious sedation: “Drug-induced lowering of consciousness during which patients respond purposefully to verbal commands, either alone or accompanied by light tactile stimulation.”
  • Minimal sedation or anxiolysis: “Drug-induced state during which patients respond normally to verbal commands.”

Local Anaesthesia

  • Regional anaesthesia: “Loss of pain sensation, with varying degrees of muscle relaxation in certain regions of the body. While traditionally administered as a single injection, newer techniques involve placement of indwelling catheters for continuous or intermittent administration of local anaesthetics.”
  • Spinal anaesthesia: “Refers to a Regional block resulting from a small volume of local anaesthetics being injected into the spinal canal.”
  • Epidural anaesthesia: “Regional block resulting from an injection of a large volume of local anaesthetic into the epidural space.”
  • Local anaesthesia: “Similar to regional anaesthesia, but exerts its effects on a smaller area of the body. Usually administered by injection to the area to be operate on by the surgeon.”