General Anaesthesia (GA) 💤

Related Subjects: | Introduction to Anaesthetics | General Anaesthetics | Spinal and Epidural Anaesthesia | Local Anaesthetics for Suturing or Other Procedures | Rapid Sequence Intubation (RSI) | Post-operative Surgical Care and Complications

General anaesthesia is a controlled, reversible, drug-induced state of: 🔇 unconsciousness • 😌 analgesia • 💪 skeletal muscle relaxation • 🛑 suppression of reflexes. It enables invasive procedures without pain or awareness while preserving oxygenation, ventilation and haemodynamic stability.

🧠 The Triad of Anaesthesia

1. Unconsciousness – cortical suppression producing amnesia and loss of awareness.
2. Analgesia – reduction of nociceptive transmission at spinal and supraspinal levels.
3. Autonomic control & muscle relaxation – maintaining cardiovascular stability and enabling surgical access.

Critical exam point: Neuromuscular blockers provide paralysis only. They do NOT provide sedation or analgesia. Awareness while paralysed is a major safety risk.

🧪 Pharmacological Principles

General anaesthetic agents shift CNS balance toward inhibition by modulating neurotransmission:

• GABA-A receptor potentiation (Propofol, volatile agents, barbiturates) → enhanced inhibitory tone.
• NMDA receptor antagonism (Ketamine) → reduced excitatory signalling + analgesia.
• Ion channel modulation (volatile agents) → altered Na⁺, K⁺ and Ca²⁺ conductance.

💊 Core Drugs Used in GA

IV Induction Agents

• Propofol – rapid onset and recovery; causes vasodilation → hypotension + respiratory depression.
• Ketamine – dissociative anaesthetic; ↑BP/HR; preserves airway reflexes; hallucinations possible.
• Etomidate – haemodynamically stable; risk of adrenal suppression.
• Thiopental – barbiturate; historically important.

Volatile (Inhalational) Agents

• Sevoflurane – smooth induction; minimal airway irritation; commonly used in paediatrics.
• Desflurane – low solubility; rapid titration and emergence.
• Isoflurane – reliable maintenance agent.
• Nitrous Oxide – weak anaesthetic; provides adjunct analgesia.

Adjunct Medications

• Opioids (Fentanyl, Remifentanil) – analgesia; blunt surgical stress response.
• Benzodiazepines (Midazolam) – anxiolysis + amnesia.
• Neuromuscular blockers (Rocuronium, Suxamethonium) – facilitate intubation and surgery.
• Reversal agents (Sugammadex, Neostigmine) – restore neuromuscular function.
• Simple analgesia (Paracetamol, NSAIDs) – multimodal postoperative pain control.

⚠️ Complications & Adverse Effects (High-Yield)

• Hypotension – vasodilation and myocardial depression (propofol, volatiles).
• Respiratory depression – reduced drive + loss of airway reflexes.
• Arrhythmias – especially volatile agents.
• Postoperative nausea & vomiting (PONV) – common; prophylaxis recommended.
• Malignant Hyperthermia
  • Triggered by volatile agents + suxamethonium
  • Signs: muscle rigidity, rising EtCO₂, hyperthermia, acidosis
  • Treatment: Dantrolene
• Anaphylaxis – commonly neuromuscular blockers or antibiotics.
• Postoperative delirium – especially elderly patients.

🖥️ Monitoring & Safety

Standard monitoring: ❤️ ECG • 📉 Blood Pressure • 💨 Pulse Oximetry • 🫁 Capnography (EtCO₂) • 🌡️ Temperature High-risk cases: arterial line, central venous access, depth of anaesthesia monitoring (BIS).

📋 Perioperative Considerations

• Pre-op assessment: Comorbidities (cardiac, respiratory, diabetes), allergies, previous anaesthetic issues.
• Positioning: Prevent nerve injury and pressure sores.
• Fluid management: Replace losses appropriately (crystalloids, blood products).
• Emergence: Monitor for airway obstruction, hypoxia, bleeding, pain.

🎯 Pain Management

Pain may be nociceptive or neuropathic. Management includes:

• Pharmacological therapy (multimodal approach)
• Regional techniques
• Physical therapy
• Psychological strategies

💉 Local & Regional Anaesthesia

• Local anaesthesia: Sodium channel blockade in small area (e.g. suturing).
• Regional anaesthesia: Nerve/plexus block (e.g. fascia iliaca, brachial plexus).
• Neuraxial anaesthesia: Spinal or epidural for lower body surgery, labour, C-section.

Regional techniques reduce opioid use, blunt the stress response, and are valuable in frail or multimorbid patients.

🛏️ Patient-Controlled Analgesia (PCA)

PCA allows patient-administered IV opioid boluses via a programmed pump with a lockout interval (e.g. morphine 1 mg with 5-minute lockout). Provides stable analgesia and reduces peaks/troughs seen with intermittent dosing.

Monitor for opioid toxicity, especially if epidural or intrathecal opioids have been used.

✨ MLA Exam Pearls:
• GA = controlled coma, not physiological sleep.
• Propofol → hypotension. Ketamine → ↑BP.
• Volatiles + suxamethonium → malignant hyperthermia.
• Always mention monitoring in OSCE/viva.
• Paralysis without sedation = catastrophic awareness risk.