Anaesthesia is a cornerstone of modern medicine, enabling pain-free surgical and medical procedures by suppressing sensation, consciousness, or reflexes. This medically induced state has revolutionised healthcare, ensuring patient safety and comfort during invasive interventions.
Why Is Anaesthesia Important?
Anaesthesia is critical for several reasons:
- Enables Complex Surgeries: Procedures like heart transplants or brain surgery are possible only because of advanced anaesthetic techniques.
- Minimises Pain and Trauma: It spares patients from experiencing physical and psychological distress.
- Ensures Patient Safety: By controlling reflexes and maintaining stability during procedures, anaesthesia helps prevent complications.
Quick Memory Tip: “Anaesthesia = Absence of sensation.”
Types of Anaesthesia
General Anaesthesia
- Definition: A complete loss of consciousness and sensation.
- Applications: Used for major surgeries such as heart, brain, or abdominal procedures.
- Administration: Delivered through IV agents or inhalation gases.
Regional Anaesthesia
- Definition: Blocks sensation in a specific region of the body.
- Types:
- Spinal Anaesthesia: Injected into the cerebrospinal fluid, often used for lower-body surgeries.
- Epidural Anaesthesia: Delivered outside the spinal cord, commonly used during childbirth.
Local Anaesthesia
- Definition: Numbs a small, specific area of the body.
- Applications: Used for minor procedures like dental work or skin biopsies.
- Delivery: Via injection, topical creams, or sprays.
Sedation
- Definition: A lighter form of anaesthesia where the patient remains conscious but relaxed.
- Applications: Common in minor procedures such as colonoscopies.
Quick Memory Tip:
- General: “Gone.”
- Regional: “Restricted region.”
- Local: “Little area.”
Mechanisms of General Anaesthesia
Phases of General Anaesthesia
- Induction:
- Administered via IV agents (e.g., propofol) or inhalation gases (e.g., sevoflurane).
- Rapid onset of unconsciousness.
- Maintenance:
- Continuous delivery of anaesthetics to sustain unconsciousness.
- Includes muscle relaxants, analgesics, and anaesthetic agents.
- Emergence:
- Gradual reduction of anaesthetics, allowing the patient to regain consciousness.
- Requires monitoring for side effects like nausea or disorientation.
Key Mechanisms
- GABA Activation: Enhances the inhibitory neurotransmitter, reducing brain excitability.
- NMDA Receptor Blockade: Prevents excitatory signals in the brain.
Quick Memory Tip: “Induce, Maintain, Emerge = Complete cycle.”
Mechanisms of Regional and Local Anaesthesia
Regional Anaesthesia (Spinal and Epidural)
- Mechanism: Blocks nerve transmission in the spinal cord, preventing sensation in the lower body.
- Key Agents: Bupivacaine, lidocaine.
Local Anaesthesia
- Mechanism: Blocks sodium channels in nerve fibres, preventing nerve conduction.
- Key Agents: Lidocaine, procaine, benzocaine.
Advantages of Regional and Local Anaesthesia
- No loss of consciousness.
- Faster recovery compared to general anaesthesia.
- Lower risk of systemic side effects.
Quick Memory Tip: “Sodium channel blockers = Stop sensation.”
Monitoring During Anaesthesia
Vital Signs
- Heart Rate (ECG): Monitors cardiac function.
- Blood Pressure: Ensures adequate perfusion.
- Oxygen Saturation (SpO₂): Monitors oxygen delivery to tissues.
Depth of Anaesthesia
- Bispectral Index (BIS): Measures brain activity to gauge the consciousness level.
Ventilation
- Capnography: Monitors CO₂ levels to ensure adequate ventilation.
Fluid and Electrolyte Balance
- Monitored through IV infusions to prevent dehydration or imbalances.
Quick Memory Tip: “Monitor Heart, Lungs, Brain, and Balance.”
Side Effects and Complications
General Anaesthesia
- Nausea and Vomiting: Common during recovery.
- Hypotension: Due to vasodilation.
- Respiratory Depression: Requires close monitoring.
- Malignant Hyperthermia: A rare but life-threatening condition; treated with dantrolene.
Regional Anaesthesia
- Spinal Headache: Caused by cerebrospinal fluid leakage.
- Nerve Damage: Rare but possible with improper technique.
Local Anaesthesia
- Allergic Reactions: Rash or swelling.
- Toxicity: Overdose can cause CNS symptoms like seizures.
Quick Memory Tip: “Watch for nausea, BP, and rare complications.”
Pharmacological Agents in Anaesthesia
Induction Agents
- Propofol: Rapid onset and short duration.
- Ketamine: Provides anaesthesia and analgesia while preserving respiratory drive.
Inhalation Agents
- Sevoflurane, Isoflurane: Used for maintenance; can cause respiratory depression.
Analgesics
- Opioids (e.g., fentanyl): Pain control during and after surgery.
Neuromuscular Blockers
- Succinylcholine, Rocuronium: Used for muscle relaxation during intubation and surgery.
Reversal Agents
- Naloxone: Reverses opioid effects.
- Neostigmine: Reverses neuromuscular blockade.
Quick Memory Tip: “Induce, maintain, and reverse with precision.”
Case Study
Patient Case
A 35-year-old woman undergoes an emergency appendectomy. She is administered propofol for induction, maintained on sevoflurane, and given fentanyl for analgesia. Post-surgery, she experiences nausea and mild hypotension.
Questions and Answers
- What type of anaesthesia was used, and why was this approach chosen?
- Answer: General anaesthesia, chosen for a major abdominal surgery requiring unconsciousness.
- What is the likely cause of post-surgery nausea and hypotension?
- Answer: Nausea from fentanyl and hypotension from sevoflurane-induced vasodilation.
- How can these side effects be managed?
- Answer: Administer antiemetic (e.g., ondansetron) and IV fluids to stabilise blood pressure.
High-Quality Revision Tips
1. “AIR: Anaesthesia Induction Routine”
To remember the sequence of General Anaesthesia:
- A: Administer induction agents (e.g., propofol, sevoflurane).
- I: Initiate maintenance with continuous delivery.
- R: Reduce dosage gradually for emergence.
2. “BLOCK: How Local and Regional Anaesthesia Works”
To recall the mechanisms of Regional and Local Anaesthesia:
- B: Block Sodium Channels.
- L: Lower Sensation in specific areas.
- O: Offer rapid recovery and minimal systemic side effects.
- C: Choose appropriate agents.
- K: Keep Consciousness.
3. “SAFE: Monitoring Essentials During Anaesthesia”
To remember the key aspects of monitoring:
- S: SpO₂ and CO₂ levels.
- A: Activity of the brain (via BIS monitor).
- F: Fluid and Electrolyte Balance.
- E: ECG and blood pressure.
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FAQs
- What is the main purpose of anaesthesia?
Anaesthesia eliminates pain and sensation during medical procedures, ensuring patient comfort and safety. - How does general anaesthesia work?
It works by enhancing inhibitory neurotransmitters like GABA and blocking excitatory signals, inducing unconsciousness. - What are the risks of regional anaesthesia?
Risks include spinal headaches and, rarely, nerve damage. - Can local anaesthesia cause side effects?
Yes, potential side effects include allergic reactions and toxicity if overdosed. - Why is monitoring crucial during anaesthesia?
Monitoring ensures the patient’s vital signs, brain activity, and fluid balance remain stable throughout the procedure.
