Introduction to Anaesthetics 💤

💉 Anaesthetics are medications and techniques that produce a controlled, reversible loss of sensation ± consciousness, enabling surgery and invasive procedures to occur safely.
Modern anaesthesia integrates pharmacology, physiology, monitoring, and organ support.
The aims are: 🛡️ safety, 😌 comfort, 🧠 amnesia, 💪 muscle relaxation, and ⚖️ stable physiology throughout the perioperative period.

📌 Categories of Anaesthesia

• 🔹 Local Anaesthesia: Loss of sensation in a small area (e.g., suturing, dental procedures).
• 🔹 Regional Anaesthesia: Nerve/plexus/neuraxial block (spinal, epidural, brachial plexus).
• 🔹 General Anaesthesia: Drug-induced unconsciousness with amnesia, analgesia and often paralysis.
• 🔹 Sedation: Reduced awareness (minimal → deep) with preserved airway reflexes in lighter levels.

🧠 The Triad of Anaesthesia

1. Unconsciousness – hypnosis and amnesia.
2. Analgesia – suppression of nociceptive signalling.
3. Autonomic control & muscle relaxation – attenuation of stress responses and facilitation of surgery.

Key principle: Neuromuscular blockers have no analgesic or hypnotic effect — paralysis without adequate anaesthesia risks awareness.

🧬 Mechanisms of Action

• Local anaesthetics: Block voltage-gated sodium channels → prevent depolarisation → stop peripheral pain transmission.
• IV/volatile agents: Enhance inhibitory pathways (GABA-A) and reduce excitatory transmission (e.g., NMDA blockade).
• Opioids: Act on μ-receptors in CNS → reduce nociceptive transmission.
• Neuromuscular blockers: Block acetylcholine at the neuromuscular junction.

💊 Common Anaesthetic Drugs

Local Anaesthetics

• Lidocaine: Rapid onset; may combine with adrenaline.
• Bupivacaine: Long-acting; cardiotoxic in overdose.
• Ropivacaine: Long-acting with improved safety profile.

IV Induction Agents

• Propofol: Rapid onset and recovery; hypotension common.
• Ketamine: Dissociative anaesthesia; ↑BP/HR; preserves airway reflexes.
• Etomidate: Haemodynamically stable; risk of adrenal suppression.

Volatile Agents

• Sevoflurane: Smooth induction; common in paediatrics.
• Desflurane: Rapid emergence.
• Isoflurane: Reliable maintenance agent.

Adjuncts

• Opioids: Fentanyl, remifentanil, morphine.
• Benzodiazepines: Midazolam.
• Neuromuscular blockers: Rocuronium, suxamethonium, atracurium.
• Simple analgesia: Paracetamol, NSAIDs.

🛠️ Essential Equipment

IV Cannulae

• Large bore (14G orange, 16G grey, 18G green) → major haemorrhage.
• Smaller gauges (20–22G) → routine medications.

Oxygen Delivery Devices

• Bag-valve mask: Up to 15 L/min; emergency ventilation.
• Nasal cannula: ≤4 L/min; low-flow oxygen.
• Simple face mask: 6–10 L/min.
• Venturi mask: Fixed FiO₂ (useful in COPD).
• Non-rebreather mask: 10–15 L/min; emergencies.

📋 Preoperative Assessment

• History: comorbidities, medications, allergies.
• Airway: Mallampati, mouth opening, neck mobility.
• Cardiorespiratory exam.
• Risk stratification using ASA grade (1–6).

Fasting Guidelines (Adults)

• Clear fluids: up to 2 hours before induction.
• Solids/milk: up to 6 hours before induction.

🧪 Surgical Stress Response

• ↑ Catecholamines → tachycardia, hyperglycaemia.
• ↑ Vasopressin → fluid retention.
• ↑ ACTH → metabolic disturbance.
• ↑ Oxygen consumption & CO₂ production.

🖥️ Standard Monitoring

• ECG
• Non-invasive BP
• Pulse oximetry
• Capnography (EtCO₂)
• Temperature
• Urine output (major cases)

⚠️ Complications

• Hypotension, arrhythmias
• Respiratory depression
• Postoperative nausea/vomiting
• Aspiration
• Postoperative delirium

✨ Clinical Pearls:
• General anaesthesia is a controlled coma — not natural sleep.
• Regional techniques reduce opioid requirements and blunt stress responses.
• Always tailor the anaesthetic plan to patient physiology and surgical demands.