Stages of General Anesthesia

Introduction to General Anesthesia

• An anaesthetic is essential for most surgical operations.
• Three main types of anaesthesia: general, regional, and local.
• Three key components of anaesthesia: analgesia, amnesia/unconsciousness, and paralysis.
• General anaesthetic facilitates a pain-free, reversible state of unconsciousness with or without paralysis.
• Comprehensive pre-operative assessments determine anaesthetic drug choice and technique, evaluating co-morbidities, fasting status, and airway assessment.

Stages of General Anesthesia

• Three stages of general anaesthetic: induction, maintenance, and emergence.

Induction Phase

• Involves securing the airway and administering drugs for rapid, smooth loss of consciousness.
• Follows the ABCDE approach:
  • A: Airway management and adjuncts.
  • B: Breathing assessment.
  • C: Cardiovascular evaluation and emergency drugs (e.g., vasopressors).
  • D: Induction includes hypnosis and muscle relaxation.
  • E: Monitoring considerations, surgery type, and duration.
  • F: Fluids and intravenous access management.
• Essential pre-operative steps include:
  • Anaesthetist's airway assessment.
  • Theatre team briefing.
  • Preparation of emergency and induction drugs.
  • Ventilator checks.
• Upon entering the anaesthetic room, essential monitoring devices are attached: ECG, blood pressure, capnography, anaesthetic depth, and SpO2.
• Pre-oxygenation with 100% oxygen for 3-5 minutes is ideal.

Airway Management

• Risk factors for airway complications necessitate securing airway via tracheal intubation over supraglottic devices.
• High-risk cases may warrant rapid sequence induction (RSI) for quick intubation to prevent airway soiling.
• RSI involves sequential administration of induction and neuromuscular blocking agents for quick unconsciousness and paralysis.
• Pre-operative airway assessment guides choice of laryngoscopy equipment and necessity for advanced tools (e.g., fibreoptic scopes).

Drugs Used in General Anesthesia

• Induction drugs are categorized into three main types and administered sequentially:
  • Pre-medication: Typically opioids or benzodiazepines to reduce doses and sympathetic stimulation.
  • Anaesthetic agents:
    • Intravenous: propofol, ketamine, thiopental, etomidate.
    • Inhaled gases: sevoflurane, desflurane, nitrous oxide.
  • Some agents (e.g., propofol, sevoflurane) serve both induction and maintenance roles.
  • Paralytic/muscle relaxant agents facilitate intubation and surgical access, especially in abdominal procedures.
  • Suxamethonium and rocuronium are commonly used for rapid sequence induction with quick onset (60 seconds and 90 seconds, respectively).

General Anaesthetic Induction Procedure

• The text outlines a simple induction "recipe" for general anaesthesia.