General Anaesthetics

Introduction & components of the anaesthetic state

• General anaesthetics (GAs) — drugs that produce a reversible loss of all sensation and consciousness with a low therapeutic index, permitting surgery and unpleasant procedures.
• Five components of the anaesthetic state — unconsciousness (hypnosis), amnesia, analgesia, immobility (inhibition of motor response to surgical stimulus) and attenuation of autonomic reflexes (± muscle relaxation) — no single agent achieves all five well.
• Balanced anaesthesia — because one drug cannot deliver all components safely, modern practice combines inhaled + IV agents (induction agent, maintenance agent, opioid analgesic, neuromuscular blocker), each chosen for a specific component.
• Objectives of GA delivery — minimise the deleterious effects of agents/techniques, sustain physiological homeostasis during surgery, and improve outcome by blunting the surgical stress response.