The components of general anaesthesia (hypnosis, analgesia, muscle relaxation)

Big picture: what “general anaesthesia” aims to achieve

• General anaesthesia is not one drug or one effect: it is a controlled state combining
  • Hypnosis (unconsciousness)
  • Analgesia (pain control)
  • Muscle relaxation (to facilitate surgery/airway management).
• Different operations need different “mixes”: e.g:
  • A short, superficial procedure may need hypnosis + analgesia only
  • Abdominal surgery often needs all three.
• Your priorities are always:
  • Oxygenation and ventilation
  • Circulation
  • And then depth / comfort / operating conditions.
• Balance benefits against side effects:
  • Deeper anaesthesia can cause hypotension and delayed wake-up
  • Too light risks awareness, movement, tachycardia, hypertension

Component 1: Hypnosis (unconsciousness / amnesia)

• Definition: reduced awareness and memory of events, patient is not responsive to verbal command.
• Common ways to provide it:
  • IV induction agents (e.g. propofol)
  • And/or inhalational agents (e.g. sevoflurane) for induction (mainly in children) and maintenance
• What you may see if hypnosis is inadequate:
  • Movement, coughing/bucking, tearing, sweating, tachycardia, hypertension (but note these can also be pain or light analgesia).
• What you may see if hypnosis is excessive:
  • Hypotension, bradycardia, delayed emergence, reduced respiratory drive (especially with IV agents/opioids).
• Practical tip: treat the cause – if the patient is moving during surgery, consider whether it is pain (analgesia), inadequate hypnosis, or lack of muscle relaxation.

Component 2: Analgesia (pain control)

• Definition: reduction of pain perception and stress response to surgery.
• Analgesia is needed even if the patient is unconscious: untreated pain can drive tachycardia, hypertension, movement, and poorer postoperative recovery.
• Common options: opioids (e.g. fentanyl/morphine), remifentanil (if using TIVA) paracetamol, NSAIDs (if appropriate), local anaesthetic infiltration, regional blocks.
• Aim for multimodal analgesia: use different drug classes/techniques to reduce opioid dose and side effects (nausea, sedation, respiratory depression).
• Signs analgesia may be inadequate (especially at incision or traction): rising heart rate/BP, sweating, lacrimation, movement (if not paralysed).
• Opioid safety: anticipate respiratory depression post-op, ensure monitoring, titrate carefully, and consider patient factors (age, OSA, frailty, renal impairment).

Component 3: Muscle relaxation (neuromuscular blockade)

• Definition: temporary paralysis of skeletal muscle using neuromuscular blocking drugs (NMBDs) to facilitate intubation and improve surgical conditions.
• Important: NMBDs do NOT provide hypnosis or analgesia—paralysed patients can still be awake and in pain if hypnosis/analgesia are inadequate.
• Common uses: tracheal intubation, laparoscopic surgery, abdominal surgery, situations where immobility is essential.
• Monitoring: use a peripheral nerve stimulator (e.g. train-of-four) to guide dosing and recovery, document findings.
• Reversal: ensure adequate recovery before extubation, use appropriate reversal strategy per local practice and drug used, and confirm clinical recovery plus objective monitoring where available.
• Practical tip: if the patient is “still” due to paralysis, you lose movement as a warning sign—pay extra attention to haemodynamics, anaesthetic delivery, and depth monitoring where used.

Putting it together: a simple “balanced anaesthetic” plan

• Before starting / WHO sign in:
  • Done with ODP and anaesthetist
  • Confirm patient details: name, date of birth, hospital number
  • Confirm procedure, confirm consent form signed and dated
  • Allergies
  • Concerns regarding aspiration risk
  • Airway plan (if not already discussed)
• Induction:
  • Lots of choices you will see. Here is a ‘common’ approach
  • If non-TIVA
    • Opioid: Fentanyl (1mcg/kg) i.e a 70kg person will receive 70mcg
    • Hypnosis: Propofol 1-2mg/kg i.e a 70kg person would receive 70 – 140 mg (7-14ml)
      • This dose varies according to age, clinical condition, patient specific factors and will therefore be higher or lower
    • Muscle relaxation: if indicated (usually for endotracheal tube placement)
      • Rocuronium:
        • 0.6mg/kg for elective / low aspirate risk
        • 1.2mg/kg for rapid sequence intubation/induction
      • Atracurium 05.mg/kg
      • Suxamethonium 1mg/kg (less commonly used outside of an RSI)
  • TIVA – in UK practice most common combinations are:
    • Processed EEG monitoring before starting medications (there are multiple options, arguably the most common is BIS. Others include NarcoTrend, Sedline)
    • Remifentanil
      • Concentration should be 50mcg/ml
      • For example, mix 1mg in 20ml of normal saline, 2mg in 40ml of normal saline
      • Different models available: Minto (effect site) is probably the most commonly used
      • Pre-induction dose: 4
    • Propofol
      • Be clear what concentration your organisation uses, this is either 1% or 2%
      • Most common models are Schnider or Eleveld
      • Induction dose:
        • Schnider 3-4
        • Eleveld 3
      • Differences between these models requires experience but these are a rough guide
    • Metaraminol
      • 10mg should be diluted up to 20ml normal saline
      • Start on 5ml/hr
• Maintenance:
  • Volatile agent or
  • TIVA for hypnosis
• Emergence:
  • Stop hypnotic
  • Ensure analgesia plan is in place
  • Reverse NMBD if used
  • Extubate only when criteria met
    • Awake enough
    • Breathing adequately
    • Protective reflexes
    • Observations relatively stable (HR / BP / oxygen saturations)

Common first-time scenarios and what to think about

• Tachycardia/hypertension at incision:
  • Often inadequate analgesia, consider opioid bolus and check vapour/infusion delivery, ensure adequate depth and exclude other causes (hypoxia, hypercarbia, light anaesthesia, full bladder, equipment issues).
• Hypotension after induction:
  • Common with hypnotics, treat with fluids/vasopressors as appropriate, reduce anaesthetic dose, and check for other causes (bleeding, anaphylaxis, arrhythmia).
• Patient moving/coughing on the tube:
  • Could be light hypnosis, inadequate analgesia, or insufficient muscle relaxation (if paralysis intended), check end-tidal agent/infusion, give analgesia, consider NMBD if appropriate.
• Poor surgical conditions (tight abdomen in laparoscopy):
  • Check NMBD depth, ventilation (CO2), and communicate with surgeon about insufflation pressure and timing.
• Slow wake-up:
  • Consider residual hypnotic/opioid effect, metabolic issues (hypothermia, hypoglycaemia), CO2 retention, or residual neuromuscular block, assess systematically and monitor closely.