Anaesthesiologislogy clinical posting imp topic for mbbs
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Anaesthesiology Clinical Posting - Important Topics for MBBS
Here is a structured, high-yield guide covering all the topics you must know during your anaesthesiology clinical posting.
1. Preoperative Assessment & Preparation
This is the foundation of anaesthetic practice. You must know:
History & Examination
- Previous anaesthesia history (adverse reactions, difficult airway, family history of malignant hyperthermia)
- Drug history - especially anticoagulants, antihypertensives, steroids, MAOIs
- Systemic comorbidities: cardiac, respiratory, hepatic, renal, DM, obesity
ASA Physical Status Classification (memorize this - asked everywhere)
| Class | Description |
|---|---|
| I | Normal healthy patient |
| II | Mild systemic disease |
| III | Severe systemic disease |
| IV | Life-threatening systemic disease |
| V | Moribund patient |
| VI | Brain-dead (organ donation) |
Fasting Guidelines (NPO Rules)
- Clear fluids: 2 hours
- Breast milk: 4 hours
- Light meal / non-human milk / formula: 6 hours
- Full meal (fried/fatty food): 8 hours
Premedication goals: Anxiolysis, analgesia, reduce secretions, reduce gastric volume/acidity, prevent aspiration
Common premedicants: Midazolam (anxiolytic), Ranitidine/PPI (reduce acid), Metoclopramide (prokinetic), Atropine (antisialagogue)
2. Airway Assessment & Management (MOST IMPORTANT PRACTICAL SKILL)
Airway Assessment - Must Know Tools:
Mallampati Classification (grade oropharyngeal visibility)
- Class I: Soft palate, uvula, fauces, pillars visible
- Class II: Soft palate, uvula, fauces visible
- Class III: Soft palate and base of uvula visible
- Class IV: Only hard palate visible
Other predictors of difficult airway:
- Mouth opening (< 3 cm = difficult)
- Thyromental distance (< 6 cm = difficult)
- Neck movements, buck teeth, receding mandible
- LEMON rule: Look, Evaluate 3-3-2, Mallampati, Obstruction, Neck mobility
Airway Equipment:
- Laryngoscope blades: Macintosh (curved - most common) vs Miller (straight)
- Endotracheal tubes (ETT): sizes 7.0-8.0 for adults
- Laryngeal Mask Airway (LMA): supraglottic device, size 3 for female, 4 for male
- Cuffed vs uncuffed ETT (children < 8 years use uncuffed)
- Bag-Valve-Mask (BVM) - basic life support
- Video laryngoscope, fibreoptic bronchoscope (for difficult airway)
Cricothyroidotomy: Emergency airway access - "can't intubate, can't oxygenate" scenario
Rapid Sequence Induction (RSI): Used in full stomach / aspiration risk patients
- Pre-oxygenation → Cricoid pressure (Sellick's manoeuvre) → Suxamethonium + Thiopentone/Propofol → Intubate
3. Types of Anaesthesia
A. General Anaesthesia (GA)
Three components (triad of anaesthesia):
- Hypnosis (unconsciousness) - IV: Propofol, Thiopentone; Inhalational: Sevoflurane, Halothane
- Analgesia - Opioids: Morphine, Fentanyl, Pethidine
- Muscle Relaxation - Succinylcholine (depolarizing), Atracurium/Vecuronium (non-depolarizing)
Stages of General Anaesthesia (Guedel's stages):
| Stage | Description |
|---|---|
| I | Analgesia (conscious, sensation decreased) |
| II | Excitement/Delirium (avoid stimulation) |
| III | Surgical anaesthesia (Planes 1-4) |
| IV | Medullary depression (overdose - avoid) |
Induction agents comparison:
| Agent | Onset | Notes |
|---|---|---|
| Propofol | Fast | Smooth induction, anti-emetic, used in TIVA |
| Thiopentone | Fast | Barbiturate, causes apnoea, contraindicated in porphyria |
| Ketamine | Fast | Dissociative; maintains airway reflexes; increases BP/HR; used in haemodynamic instability |
| Etomidate | Fast | Least cardiovascular depression; inhibits adrenal cortex |
Inhalational agents:
- Sevoflurane: Induction of choice (children), pleasant smell, safe
- Isoflurane: Maintenance, coronary steal (caution IHD)
- Halothane: Hepatotoxicity risk (halothane hepatitis), arrhythmias
- Nitrous oxide (N₂O): Analgesic/adjuvant; expands gas-filled cavities (avoid in pneumothorax, bowel obstruction)
MAC (Minimum Alveolar Concentration): Concentration at which 50% of patients don't move to skin incision. Lower MAC = more potent.
- Halothane: 0.75%; Isoflurane: 1.15%; Sevoflurane: 2%; Desflurane: 6%; N₂O: 104%
B. Regional Anaesthesia
Spinal Anaesthesia:
- Injection of local anaesthetic into the subarachnoid/intrathecal space (usually L3-L4 or L4-L5)
- Rapid onset, intense block
- Used for: lower limb, obstetric (LSCS), pelvic, perineal surgery
- Drugs: Hyperbaric bupivacaine 0.5%; opioids (fentanyl) added for prolonged analgesia
- Complications: Post-dural puncture headache (PDPH), hypotension, high spinal, urinary retention
- Sympathetic block → hypotension (especially above T10)
- PDPH minimised by fine-bore pencil-tip (atraumatic) needles
- Bailey and Love's Surgery, block3
Epidural Anaesthesia:
- Local anaesthetic injected into the epidural space
- Slower onset than spinal, but catheter allows top-ups and continuous infusion
- Uses: Labour analgesia, postoperative pain (thoracic/abdominal surgery), chronic pain
- Complications: Dural puncture, accidental total spinal, nerve damage, epidural haematoma, infection
- Technically more difficult, higher failure rate than spinal
- Bailey and Love's Surgery, block3
Nerve Blocks:
- Brachial plexus blocks: Interscalene (shoulder), Supraclavicular, Infraclavicular, Axillary (upper limb)
- Femoral + Sciatic blocks (lower limb)
- TAP (Transversus Abdominis Plane) block: abdominal surgery analgesia
- Ultrasound guidance is now standard
- Bailey and Love's Surgery, block3
Local Anaesthetic Techniques:
- EMLA cream (Lidocaine + Prilocaine) for venepuncture in children
- Moffett's solution (Cocaine + Adrenaline + NaHCO₃) for nasal surgery
- Lidocaine spray for awake fibreoptic intubation
4. Local Anaesthetic Agents
| Drug | Duration | Notes |
|---|---|---|
| Lignocaine (Lidocaine) | Short | Max dose 3 mg/kg (7 mg/kg with adrenaline) |
| Bupivacaine | Long | Cardiotoxic in overdose; 0.5% hyperbaric for spinal |
| Ropivacaine | Long | Less cardiotoxic than bupivacaine |
| Cocaine | Short | Only LA with vasoconstriction; used in nasal surgery |
Mechanism: Block voltage-gated Na⁺ channels → prevent action potential propagation
LA Toxicity (LAST): Perioral tingling → seizures → cardiovascular collapse
Treatment: Stop LA, ABC, IV Lipid emulsion 20% (Intralipid)
Order of nerve fibre blockade: B > C > Aδ > Aγ > Aβ > Aα (smallest first)
5. Muscle Relaxants
Depolarizing:
- Succinylcholine (Suxamethonium): Rapid onset (60 sec), short duration (10 min); used for RSI and laryngospasm
- Fasciculations → ↑K⁺ (avoid in burns, crush injury, denervation after 24h)
- Contraindicated in: Hyperkalemia, personal/family h/o malignant hyperthermia, pseudocholinesterase deficiency
Non-depolarizing:
| Agent | Duration | Notes |
|---|---|---|
| Vecuronium | Intermediate | Cardiovascularly stable |
| Atracurium | Intermediate | Hofmann elimination; safe in renal/hepatic failure |
| Pancuronium | Long | Tachycardia, avoid in IHD |
| Rocuronium | Intermediate | Can be reversed by Sugammadex |
Reversal of NMB: Neostigmine (anti-cholinesterase) + Atropine (to prevent bradycardia/secretions)
Sugammadex: Reverses Rocuronium/Vecuronium directly (encapsulates drug)
6. Monitoring in Anaesthesia
Minimum standard monitoring (ASA standards):
- Pulse oximetry (SpO₂)
- NIBP (non-invasive blood pressure)
- ECG
- Capnography (EtCO₂) - Gold standard for confirming ETT placement
- Temperature
Additional monitoring:
- IBP (invasive arterial line): For major surgery, haemodynamic instability
- CVP (Central venous pressure): Fluid status
- Train-of-Four (TOF): Assess neuromuscular blockade recovery
- BIS (Bispectral index): Depth of anaesthesia
- Urine output: > 0.5 mL/kg/hr indicates adequate perfusion
EtCO₂ (Capnography) - Critical:
- Normal: 35-45 mmHg
- Confirms ETT in trachea (not oesophagus)
- Sudden drop → disconnection, cardiac arrest, PE
- Gradual rise → hypoventilation, malignant hyperthermia
7. Anaesthetic Complications (High Yield)
Malignant Hyperthermia (MH)
- Autosomal dominant, mutation in RYR1 (ryanodine receptor)
- Triggered by: Succinylcholine + volatile anaesthetics (halothane, sevoflurane, isoflurane)
- Features: Hyperthermia, muscle rigidity, ↑EtCO₂, tachycardia, metabolic acidosis, hyperkalemia
- Treatment: Dantrolene (2.5 mg/kg IV), stop trigger agents, cooling, supportive care
Aspiration (Mendelson's Syndrome)
- Acid aspiration → chemical pneumonitis
- Prevention: Fasting, RSI + cricoid pressure, NG tube decompression
- Treatment: Supportive (steroids controversial)
Post-Dural Puncture Headache (PDPH)
- Positional headache (worse on sitting/standing)
- Due to CSF leakage at dural puncture site
- Rx: Bed rest, hydration, analgesics, caffeine; Epidural blood patch (gold standard)
Laryngospasm
- Reflex closure of vocal cords
- Partial: CPAP with 100% O₂; Total: Succinylcholine 0.5-1 mg/kg
Bronchospasm
- Wheeze, ↑peak airway pressure, ↓SpO₂
- Rx: Deepen anaesthesia, bronchodilators (salbutamol), steroids
8. Postoperative Care & PACU
Post-Anaesthetic Care Unit (PACU) - Recovery Room:
- Patient stays until Aldrete score ≥ 9
- Aldrete Score: Activity, Respiration, Circulation, Consciousness, SpO₂ (each 0-2)
Common postoperative problems:
| Problem | Cause | Management |
|---|---|---|
| Nausea/Vomiting (PONV) | Opioids, N₂O, motion | Ondansetron, Metoclopramide, Dexamethasone |
| Shivering | Hypothermia | Warm blankets, Pethidine 25 mg IV |
| Pain | Surgery | WHO analgesic ladder, multimodal analgesia |
| Delayed awakening | Drug accumulation | Reversal agents, supportive care |
| Desaturation | Airway obstruction, atelectasis | O₂, jaw thrust, repositioning |
9. Pain Management
WHO Analgesic Ladder (3 steps):
- Non-opioid: Paracetamol, NSAIDs (ketorolac, diclofenac)
- Mild opioid + Non-opioid: Tramadol, Codeine
- Strong opioid + Non-opioid: Morphine, Fentanyl, Oxycodone
Routes: Oral > Transdermal > Subcutaneous > IV > Epidural > Intrathecal
Patient Controlled Analgesia (PCA): Patient self-administers small IV opioid doses; improves satisfaction and reduces over/under-dosing.
Multimodal Analgesia: Combining different analgesic classes to reduce opioid consumption and side effects - paracetamol + NSAID + opioid + regional block.
10. Special Topics (Frequently Asked)
Ketamine
- NMDA receptor antagonist
- Dissociative anaesthesia: Analgesia + amnesia + sedation but eyes open, reflexes maintained
- Increases HR, BP, bronchodilator (ideal in haemodynamically unstable, asthma, EM setting)
- Side effects: Emergence delirium (counteracted with midazolam), hypersalivation, raises ICP
- Contraindicated: Hypertension, raised ICP, open eye injury, severe CAD
Total Intravenous Anaesthesia (TIVA)
- Uses Propofol infusion ± Remifentanil for maintenance (no volatile agents)
- Advantages: Less PONV, useful when volatile agents contraindicated (MH risk, PONV-prone)
Fluid Management
- Maintenance: 4-2-1 rule (4 mL/kg for first 10 kg, 2 mL/kg for next 10 kg, 1 mL/kg for remaining)
- Crystalloids (Normal saline, Ringer's Lactate) vs Colloids (Albumin, Gelofusine)
- Blood transfusion threshold: Hb < 7 g/dL (otherwise < 8 in cardiac patients)
High Spinal
- LA rises to cervical cord → respiratory arrest, hypotension, loss of consciousness
- Management: ABC, vasopressors (ephedrine/phenylephrine), intubation if needed
Quick Revision Table - Must-Know Drugs
| Drug | Class | Key Point |
|---|---|---|
| Propofol | IV induction | Pain on injection, anti-emetic, TIVA, PRIS on prolonged use |
| Thiopentone | IV induction | Barbiturate, porphyria contraindicated, fits in sub-anaesthetic doses |
| Ketamine | IV induction | Dissociative, bronchodilator, raises ICP, MH safe |
| Suxamethonium | Depolarizing NMB | RSI agent, fasciculations, ↑K⁺, triggers MH |
| Atracurium | Non-dep NMB | Hofmann elimination, histamine release |
| Rocuronium | Non-dep NMB | Reversed by Sugammadex |
| Neostigmine | Reversal | Muscarinic effects - give with atropine |
| Dantrolene | MH treatment | Acts on ryanodine receptor, reduces Ca²⁺ release |
| Fentanyl | Opioid | 100x potent vs morphine, short acting, epidural/spinal adjuvant |
| Ondansetron | Anti-emetic | 5-HT₃ antagonist, PONV first line |
Clinical Posting Practical Skills Checklist
During your posting, aim to:
- Observe/assist in preoperative assessment and consent
- Perform airway assessment (Mallampati, TMD, mouth opening)
- Observe induction of general anaesthesia
- Observe ETT insertion and confirm with capnography
- Assist in spinal/epidural anaesthesia setup
- Monitor a patient on the anaesthesia machine (SpO₂, EtCO₂, NIBP)
- Observe recovery room management
- Prescribe postoperative analgesia (under supervision)
Sources:
- Bailey and Love's Short Practice of Surgery, 28th Ed. - Anaesthesia chapter (Spinal, Epidural, Local anaesthetics, Pain)
- Morgan and Mikhail's Clinical Anesthesiology, 7e
- Barash, Cullen & Stoelting's Clinical Anesthesia, 9e
- Miller's Anesthesia, 10e
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