AIM STEP 10
Student Memory Support
Regional and Neuraxial Anaesthesia, Local Anaesthetics, Preoperative Assessment and Monitoring
4th Year MBBS • Neuroscience • High-yield memory reinforcement and last-minute revision
1. High-Yield Flashcards
Tap each question to reveal the answer.
Q: What is the key difference between general and regional anaesthesia?
A: General anaesthesia produces unconsciousness; regional anaesthesia blocks sensation from a selected body region.
Q: Which two main methods are used to induce general anaesthesia?
A: Intravenous induction and inhalational induction.
Q: Where is local anaesthetic deposited during spinal anaesthesia?
A: Into the subarachnoid space, where it mixes with cerebrospinal fluid.
Q: What makes epidural anaesthesia useful for prolonged procedures?
A: An epidural catheter allows repeated doses or continuous local anaesthetic infusion.
Q: Through which anatomical opening is a caudal epidural block approached?
A: Through the sacral hiatus.
Q: What is the principal advantage of combined spinal–epidural anaesthesia?
A: Rapid spinal onset combined with the ability to extend the block through an epidural catheter.
Q: What is the main purpose of preoperative anaesthetic evaluation?
A: To identify perioperative risk, optimize problems, plan the anaesthetic technique and determine monitoring needs.
Q: What does ASA IV indicate?
A: Severe systemic disease that is a constant threat to life.
Q: Which monitor gives continuous information about exhaled carbon dioxide?
A: Capnography.
Q: How are ester and amide local anaesthetics mainly metabolised differently?
A: Esters are mainly hydrolysed by plasma esterases; amides are mainly metabolised in the liver.
Q: What drugs are combined in EMLA?
A: Lignocaine and prilocaine.
Q: What is the primary molecular target of local anaesthetic drugs?
A: Voltage-gated sodium channels on the intracellular side of the nerve membrane.
Q: Why may local anaesthesia be less effective in markedly acidic inflamed tissue?
A: Less drug remains in the uncharged form needed to cross the nerve membrane.
Q: What is meant by differential nerve blockade?
A: Different nerve fibers are blocked at different sensitivities, with sympathetic and pain fibers generally affected before large motor fibers.
Q: Why does adrenaline prolong the effect of infiltrated lignocaine?
A: It causes local vasoconstriction, reducing blood flow and slowing systemic removal of lignocaine.
Q: Which local anaesthetic is particularly important for severe cardiotoxicity?
A: Bupivacaine.
2. Mnemonics
Mnemonic Title: ASA Severity Progression
H–M–S–T–M–D
Meaning: Healthy → Mild disease → Severe disease → Threat to life → Moribund → Donor.
Mnemonic Title: Differential Block Sequence
S-P-T-M
Meaning: Sympathetic → Pain/temperature → Touch/pressure → Motor function.
Mnemonic Title: Local Anaesthetic Systemic Toxicity
N-C
Meaning: Neurological toxicity → Cardiovascular toxicity, progressing from CNS symptoms/seizures to arrhythmia and cardiovascular collapse.
3. Memory Tables
Spinal vs Epidural Anaesthesia
| Feature | Spinal | Epidural |
|---|---|---|
| Drug location | Subarachnoid space | Epidural space |
| Onset | Rapid | More gradual |
| Drug quantity | Relatively small | Larger amount required |
| Extension | Single injection usually | Catheter allows extension |
Ester vs Amide Local Anaesthetics
| Feature | Esters | Amides |
|---|---|---|
| Examples | Procaine, tetracaine, benzocaine, cocaine | Lignocaine, bupivacaine, prilocaine, ropivacaine |
| Main metabolism | Plasma esterases | Liver |
| Allergy association | Relatively greater | Less common |
4. Rapid Revision Points — Last-Minute Revision
Must Remember:
- Regional anaesthesia blocks sensation from a selected body region without necessarily producing unconsciousness.
- Spinal anaesthesia places local anaesthetic in CSF; epidural anaesthesia places it outside the dura.
- Caudal block is an epidural technique approached through the sacral hiatus.
- An epidural or peripheral nerve catheter permits prolonged or continuous local anaesthetic administration.
- ASA class describes preoperative physical status; the suffix E indicates emergency surgery.
- Pulse oximetry reflects oxygen saturation, whereas capnography provides information about ventilation.
- Local anaesthetics block voltage-gated sodium channels and prevent action-potential propagation.
- Greater tissue blood flow increases systemic absorption and may shorten local anaesthetic action.
- Adrenaline prolongs lignocaine action by local vasoconstriction and also reduces operative-site bleeding.
- 1:200,000 adrenaline = 5 micrograms/mL; 1:80,000 = 12.5 micrograms/mL.
5. Clinical Memory Hooks
Hypotension after spinal anaesthesia → sympathetic blockade → vasodilatation and reduced vascular tone.
Painful inflamed acidic tissue → less uncharged local anaesthetic crosses the nerve membrane → weaker local block.
Circumoral numbness, tinnitus and seizure after a nerve block → excessive systemic local anaesthetic exposure.
Severe arrhythmia after accidental intravascular local anaesthetic injection → consider bupivacaine cardiotoxicity.
6. Starred High-Yield Exam Points
- ⭐ Spinal anaesthesia = subarachnoid injection; epidural anaesthesia = drug outside the dura.
- ⭐ Local anaesthetics block voltage-gated sodium channels from the intracellular side.
- ⭐ Differential blockade generally affects sympathetic and pain fibers before large motor fibers.
- ⭐ Adrenaline with lignocaine reduces local blood flow, prolongs action and reduces systemic absorption.
- ⭐ Bupivacaine is the major local anaesthetic associated with serious cardiotoxicity.
- ⭐ Prilocaine and benzocaine are important local anaesthetics associated with methemoglobinemia.