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DNB Final Exam — Paper 1, Post Diploma (FAT 2025)

Complete Model Answers

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Q1. Oxygen Cascade and Dissociation Curve

Oxygen Cascade

• At sea level: PAO₂ = 0.21 × (760 − 47) − 40/0.8 ≈ 100 mmHg
• A–a gradient: normally <15 mmHg (increases with V/Q mismatch, shunt, diffusion defect)

Oxyhaemoglobin Dissociation Curve (ODC)

• Sigmoid shape due to cooperative binding (T→R state transition of Hb)
• P50 = 26.5 mmHg (normal); at this PO₂, Hb is 50% saturated

• ↑CO₂ (Bohr effect), ↑H⁺ (↓pH), ↑Temperature, ↑2,3-DPG, Stored blood (initially ↑2,3-DPG depleted)

• ↓CO₂, ↓H⁺ (↑pH), ↓Temperature, ↓2,3-DPG, Fetal Hb (HbF), CO poisoning, MetHb

• Hypothermia during CPB shifts curve left — O₂ delivery maintained by ↑CO
• Stored blood: 2,3-DPG depleted after 1 week → left shift → impaired tissue O₂ delivery
• Massive transfusion → transient left shift

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Q2. Desflurane and Remifentanil

Desflurane

• Fastest emergence and recovery (ideal in day care, obese patients, neuroanaesthesia)
• Minimal metabolism → no organ toxicity
• Low solubility → rapid titration

• Airway irritant — causes coughing, laryngospasm, bronchospasm (avoid for inhalational induction)
• ↑SVR, ↑HR on rapid increases in concentration (sympathetic stimulation)
• ↑Cerebral blood flow and ICP (at >1 MAC) — use with caution in neurosurgery
• Reacts with dry CO₂ absorbent → CO production
• GWP (global warming potential) = 2540 (environmental concern; being phased out in UK/Europe)
• Requires a unique, electrically heated vaporizer (Tec 6)

Remifentanil

• Predictable, rapid offset regardless of infusion duration — ideal for TIVA/TCI
• Organ-independent metabolism → safe in hepatic/renal failure
• Blunts intubation response (1–1.5 mcg/kg bolus)
• Infusion: 0.05–2 mcg/kg/min

• No residual analgesia after stopping → must provide multi-modal analgesia pre-emptively
• Opioid-induced hyperalgesia (OIH) with prolonged high-dose infusion
• Bradycardia and hypotension
• Muscle rigidity at high bolus doses
• Susceptible to context-dependent hypoventilation
• Not suitable as sole agent — must be combined with hypnotic

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Q3. Capnography and Neuromonitoring

Capnography

• Phase I: Inspiratory baseline (EtCO₂ = 0; dead space gas)
• Phase II: Expiratory upstroke (mixing of dead space and alveolar gas)
• Phase III: Alveolar plateau (EtCO₂ peaks ~35–45 mmHg)
• Phase 0: Inspiratory downstroke

1. Confirmation of ETT placement (most reliable method)
2. Monitoring ventilation adequacy
3. Detecting oesophageal intubation (flat trace)
4. Detecting air embolism (sudden ↓ EtCO₂)
5. Detecting endobronchial intubation
6. ROSC during CPR (sudden ↑ EtCO₂ >40 mmHg)
7. Monitoring metabolic rate (↑ in MH, thyroid storm)
8. Guide to diagnosis: shark-fin pattern = bronchospasm; plateau disappears = sampling error

Neuromonitoring (Intraoperative Neurophysiological Monitoring – IONM)

• Volatile agents suppress SSEP/MEP in dose-dependent manner (avoid >0.5 MAC)
• TIVA preferred for MEP monitoring (Propofol + Remifentanil)
• Neuromuscular blockade abolishes MEP (avoid if MEP monitoring)
• Nitrous oxide suppresses MEPs
• Maintain MAP >80 mmHg, normothermia, normocapnia

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Q4. Shockable and Non-Shockable Rhythms; Management of Pulseless Rhythm

Shockable Rhythms

1. Ventricular Fibrillation (VF)
2. Pulseless Ventricular Tachycardia (pVT)

Non-Shockable Rhythms

1. Pulseless Electrical Activity (PEA)
2. Asystole

Management of Pulseless Rhythm (Adult ALS Algorithm 2021)

• Call for help, start CPR (30:2 ratio), attach defibrillator
• High-quality CPR: Rate 100–120/min, depth 5–6 cm, full chest recoil, minimize interruptions

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1. Deliver 1 shock (200 J biphasic, or 360 J monophasic)
2. Immediately resume CPR × 2 minutes
3. After 2 min → reassess rhythm
4. If VF/pVT persists → 2nd shock → CPR 2 min
5. After 3rd shock: Adrenaline 1 mg IV + Amiodarone 300 mg IV
6. Subsequent adrenaline every 3–5 min (alternate cycles)
7. After 5th shock: Amiodarone 150 mg additional dose (if VT/VF refractory)

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1. Continue CPR 30:2
2. Adrenaline 1 mg IV immediately (as soon as IV access obtained)
3. Adrenaline every 3–5 min
4. Treat reversible causes (4H + 4T)

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• Adrenaline: 1 mg IV/IO every 3–5 min
• Amiodarone: 300 mg IV bolus (shockable, after 3rd shock), then 150 mg after 5th shock
• If no amiodarone: Lignocaine 100 mg IV (1–1.5 mg/kg)

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Q5. Fascia Iliaca Block

• Target: Femoral nerve, Lateral femoral cutaneous nerve (LFCN), and partially obturator nerve
• Fascia iliaca = fibrous sheet over the iliopsoas muscle
• LA is deposited deep to the fascia iliaca, lateral to the femoral vessels

• Hip fracture (fractured neck of femur) — excellent for perioperative analgesia
• Total hip arthroplasty (THA), Total knee arthroplasty (TKA)
• Femoral shaft fractures, ORIF procedures
• As alternative to femoral nerve block or 3-in-1 block

1. Landmark-based (Dalens' method): 1 cm below junction of lateral 1/3 and medial 2/3 of inguinal ligament; loss of resistance at 2 fascia pops (fascia lata + fascia iliaca)
2. Infrainguinal US-guided: Femoral vessels identified; LA deposited between fascia iliaca and iliopsoas lateral to femoral nerve
3. Suprainguinal US-guided: Above inguinal ligament; better spread toward obturator nerve; preferred for hip surgery (PENG block alternative)

• Femoral nerve (L2-L4) — reliably
• LFCN (L2-L3) — reliably
• Obturator nerve (L2-L4) — variably (better with suprainguinal approach)

• Covers larger area, single injection for 3 nerves
• Less risk of femoral nerve injury (not targeting nerve directly)

• LA systemic toxicity (LAST) — use max recommended dose
• Femoral vessel puncture
• Intravascular injection
• Quadriceps weakness/fall risk (femoral block effect)
• Hematoma

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Q6. Methods to Reduce ICP and Maintain Cerebral Perfusion Pressure

Normal Values

• ICP: <15 mmHg (normal 5–15 mmHg)
• CPP = MAP − ICP (target CPP ≥60–70 mmHg in TBI)

Methods to Reduce ICP

• Head-up 30° (reduces venous congestion)
• Head midline (prevents jugular venous obstruction)

• Hyperventilation: ↓PaCO₂ → cerebral vasoconstriction → ↓CBF → ↓ICP
• Target PaCO₂ 35 mmHg (mild hyperventilation); avoid <30 mmHg (ischemia risk)
• Avoid hypoxia (maintain SpO₂ >94%)

• Mannitol 20%: 0.25–1 g/kg IV over 20–30 min; osmotic diuresis; onset 20–40 min; avoid if serum osmolality >320 mOsm/L
• Hypertonic saline (3% NaCl): Equal or superior to mannitol; preferred in hypovolaemia/haemodynamic instability; Na+ target 145–160 mEq/L

• Propofol infusion: ↓CMRO₂, ↓CBF, ↓ICP; allows burst suppression at high doses
• Midazolam/fentanyl for ICU sedation
• Barbiturates (thiopentone): Reduce CMRO₂ 50–55%; second-line for refractory ICP
• Avoid ketamine (historically; now used cautiously as it may not raise ICP if normocapnia maintained)

• Ventriculostomy (EVD): Direct ICP measurement + drainage — most effective
• Lumbar drain: Only when basal cisterns are patent

• Dexamethasone: Effective for vasogenic oedema (tumour, abscess) — NOT recommended in TBI (CRASH trial showed ↑ mortality)

• Prevents rises in ICP from coughing, Valsalva, patient–ventilator dyssynchrony

• Avoid hyperthermia (fever raises CMRO₂ and ICP)
• Mild hypothermia (32–35°C) can reduce ICP — limited evidence for outcomes in TBI

• Decompressive craniectomy (refractory ICP >25 mmHg)
• Evacuation of haematoma/mass lesion

• ↓ ICP: Propofol, barbiturates, benzodiazepines, opioids (if normocapnia), etomidate, lignocaine
• ↑ ICP (avoid): Ketamine (relative), volatile agents >1 MAC, N₂O, succinylcholine (transient)
• ↑ CPP: Vasopressors (noradrenaline, phenylephrine) to raise MAP

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Q7. Anaesthesia Management: 80-year-old Diabetic and Hypertensive for Unilateral TKR

Preoperative Assessment

• Diabetes: HbA1c ideally <8.5%; check renal function (metformin — stop 48h before if eGFR <60); check for autonomic neuropathy, gastroparesis
• Hypertension: Optimise BP <160/100 pre-op; continue antihypertensives on morning of surgery (except ACEI/ARB — omit on day of surgery to avoid intraoperative hypotension); ECG for LVH, rhythm
• Cardiac evaluation: Functional capacity (METs); echocardiogram if poor functional capacity; consider stress testing if significant cardiac risk
• Airway: Assess for DM-related atlantoaxial/cervical stiffness, limited mouth opening
• Investigations: CBC, RFT, LFT, electrolytes, ECG, CXR, blood glucose, HbA1c, coagulation if neuraxial planned

Anaesthetic Options

• Hyperbaric bupivacaine 0.5% (2–3 mL) ± fentanyl 25 mcg or morphine 100 mcg
• Advantages: Avoids GA, excellent block, reduced blood loss, reduced DVT, early mobilisation
• Caution: Hypotension more pronounced in hypertensive/elderly → pre-load with crystalloid, have vasopressor ready (phenylephrine/ephedrine)
• Block level: T12–L1 sufficient for TKR

• Allows extending block duration
• Useful if surgery expected >2.5 hrs

• Anticoagulation, patient refusal, severe spinal stenosis
• Use LMA if possible; TIVA preferable in elderly
• Avoid long-acting opioids; use multimodal analgesia

Perioperative Considerations

• Target glucose 6–10 mmol/L intraoperatively
• Monitor glucose every 1–2 hours
• Variable rate insulin infusion (VRII) if glucose poorly controlled
• Avoid hypoglycaemia (worse than mild hyperglycaemia)

• Maintain MAP within 20% of baseline
• Spinal-induced hypotension: treat with fluids + vasopressors
• Avoid intraoperative hypertension (LA use in surgical field, tourniquet inflation)

• Mechanical: Pneumatic compression devices, TED stockings
• Pharmacological: LMWH (enoxaparin) — timing based on anaesthetic technique

• Femoral nerve block / Adductor canal block (ACB): Preferred — preserves quadriceps strength (important for rehab); ACB: 15–20 mL 0.5% ropivacaine
• Fascia iliaca block as alternative
• Periarticular infiltration by surgeon (ropivacaine + ketorolac + epinephrine)
• Paracetamol 1g IV/oral QID (safe in elderly)
• NSAIDs cautiously (impaired renal function in elderly/diabetic)
• Avoid systemic opioids (confusion, urinary retention in elderly)

• Standard inflation pressure 250–300 mmHg (100 mmHg above systolic in hypertensive)
• Tourniquet time <90 min; pain from tourniquet (ischaemic pain) under spinal after ~45 min

• Continue antihypertensives and insulin regimen
• Early mobilisation Day 1
• Blood glucose monitoring 4-hourly for 24h post-op
• Restart metformin when eating and renal function confirmed normal

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Q8. Equipment Used in OLV — Describe DLT, Indications, and Complications

Equipment for One-Lung Ventilation (OLV)

• Cohen Flexitip BB, Arndt BB, Fuji Uniblocker, EZ-Blocker, Larndt, Lernaite (SLT) 3. Univent Tube — single-lumen tube with built-in bronchial blocker channel 4. Single-Lumen Tube — advanced into main bronchus (emergency)

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Double-Lumen Tube (DLT)

• Two lumens: tracheal lumen + bronchial lumen
• Two cuffs: tracheal cuff (white/clear) + bronchial cuff (blue/coloured)
• Bronchial lumen: 15 mm shorter, enters left or right main bronchus
• 4-connector (blue = bronchial, clear = tracheal)

• Females: 35–37F; Males: 39–41F

• Left DLT: Bronchial limb enters left main bronchus — preferred in most cases (longer left main bronchus = wider safety margin)
• Right DLT: Has Murphy eye (ventilation hole) for right upper lobe; used when left bronchus is involved (left pneumonectomy, left bronchial surgery, left main stem tumour/stricture)

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Indications for OLV/DLT

1. Prevent contamination of healthy lung: pulmonary abscess, massive haemoptysis, empyema (pus), bronchopleural fistula
2. Differential lung ventilation (different PEEP each lung)
3. Unilateral bronchopulmonary lavage (pulmonary alveolar proteinosis)

1. Pulmonary resection (pneumonectomy, lobectomy, segmentectomy)
2. Oesophagectomy (thoracoscopic or open)
3. Thoracic aortic surgery (VATS, descending aorta)
4. Anterior thoracic spine surgery
5. VATS procedures
6. Minimally invasive cardiac surgery

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Complications of DLT

1. Malposition — most common
   • Too deep: enters wrong bronchus → collapse of both lungs
   • Too shallow: both lungs ventilated, no isolation
   • Right DLT: Murphy eye may obstruct RUL → RUL collapse
2. Hypoxia during OLV: V/Q mismatch, ↑ shunt (non-ventilated lung)
3. Airway trauma: Tracheobronchial rupture (overinflation of bronchial cuff — inflate with minimum volume to seal)
4. Tooth/airway damage during insertion (large tube)
5. Obstruction: Secretions, blood

1. Sore throat, hoarseness
2. Bronchial rupture (rare) — more risk with right DLT

• FiO₂ → increase to 1.0
• Lung recruitment of dependent (ventilated) lung
• Apply PEEP to dependent lung (5–10 cmH₂O)
• PEEP/CPAP to non-dependent (collapsed) lung
• inform surgeon to allow intermittent re-expansion

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Q9. Difficult Airway Algorithm and Blocks Used in Awake Fibreoptic Intubation

Difficult Airway Algorithm (ASA/DAS 2022 approach)

1. Preoxygenation (mandatory — 3 min tidal breathing or 8 vital capacity breaths with FiO₂ = 1.0)
2. Direct laryngoscopy × 2 attempts → if failed → declare difficult intubation
3. Facemask ventilation (maintain oxygenation)
4. Plan B: Video laryngoscope, different blade, stylet/bougie
5. Plan C: Supraglottic airway (SGA: LMA/iGel)
6. Plan D (CICO — Cannot Intubate, Cannot Oxygenate):
   • Front-of-neck airway (FONA): Surgical cricothyrotomy (scalpel-finger-bougie technique) — preferred in emergency
   • Needle cricothyrotomy (temporizing measure)

• Limit intubation attempts (maximum 3 + 1 by expert)
• Call for help early
• Avoid multiple blind attempts
• Maintain oxygenation at every step
• "If in doubt, don't" — wake up, abandon if non-emergent

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Awake Fibreoptic Intubation (AFOI)

• Predicted difficult airway (Mallampati III/IV, short neck, limited neck extension, OSA)
• Cervical spine instability (trauma, RA, ankylosing spondylitis)
• Previous failed intubation
• TMJ ankylosis, pharyngeal mass
• Obese with multiple predictors

• Antisialogogue: Glycopyrrolate 0.2–0.3 mg IM/IV (30 min before) — dries secretions, improves visibility
• Anxiolytic: Midazolam 1–2 mg IV

• Dexmedetomidine 1 mcg/kg over 10 min, then 0.2–0.7 mcg/kg/hr — preferred (sedation without respiratory depression, cooperative patient)
• Remifentanil TCI (target 1–2 ng/mL) — co-sedation
• Fentanyl 25–50 mcg aliquots
• Avoid heavy sedation (defeats the purpose of AFOI)

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Regional Blocks for AFOI

• Co-phenylcaine spray (lignocaine + oxymetazoline) or cocaine 4% (nasal decongestant + anaesthetic)
• Nasal airway lubricated with lignocaine gel

• Anaesthetises the laryngeal mucosa above vocal cords (epiglottis, aryepiglottic folds, arytenoids)
• Technique: Lateral approach — identify thyrohyoid membrane, inject 2 mL 2% lignocaine beneath each cornu of the hyoid bone, just lateral to midline
• Target nerve: Internal branch of SLN

• Anaesthetises the mucosa below the vocal cords (trachea)
• Technique: 22G needle through cricothyroid membrane in midline, confirm air aspiration, inject 2–4 mL 4% lignocaine at end-expiration → immediate cough distributes LA
• Provides anaesthesia from cords to carina

• Anaesthetises the oropharynx, posterior tongue, tonsillar pillars
• Technique: Peritonsillar injection at posterior palatoglossal arch (tonsillar pillar) with 2 mL 1% lignocaine; risk of carotid artery puncture
• Alternative: Anterior tonsillar pillar approach

• 10% lignocaine spray to oropharynx and tongue
• Nebulised 4% lignocaine (preferred — no block needed, safe): 4 mL via nebuliser over 20 min — covers from nose to trachea

• Nebulised lignocaine 4% (4 mL)
• Topical 10% lignocaine spray to posterior pharynx
• Transtracheal block 4% lignocaine
• ± SLN block

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Q10. Malignant Hyperthermia and Compartment Syndrome

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A. Malignant Hyperthermia (MH)

• All volatile agents (halothane, sevoflurane, isoflurane, desflurane)
• Succinylcholine
• (Stress, exercise — for exercise-induced MH variants)

• Propofol, midazolam, ketamine, opioids, all NMBDs except succinylcholine, local anaesthetics, N₂O (safe)

• Masseter muscle rigidity (esp. after succinylcholine)
• ↑ EtCO₂ (earliest and most sensitive sign — CO₂ production soars)
• Tachycardia, tachypnoea
• Generalised muscle rigidity
• Hyperthermia (temperature rise 1–2°C every 5 min → can reach >42°C)
• Metabolic + respiratory acidosis

• Hyperthermia (prominent)
• Rhabdomyolysis → dark urine (myoglobinuria)
• ↑CPK (>20,000 IU/L)
• Hyperkalaemia (cardiac arrhythmias → VF)
• Acute renal failure
• DIC
• Cardiac arrhythmias

1. Call for help — dedicated MH team
2. Stop all triggering agents (volatile agent off, stop succinylcholine)
3. Flush anaesthesia machine — high O₂ flow (≥10 L/min) × 10 min; change circuit + soda lime
4. Maintain surgery if life-threatening; otherwise conclude and wake up
5. Dantrolene — definitive treatment
   • Initial dose: 2.5 mg/kg IV (rapid bolus)
   • Repeat 1 mg/kg boluses every 5 min until symptoms controlled
   • Total dose: up to 10 mg/kg (or more if needed)
   • Mechanism: Blocks ryanodine receptor (RyR1), preventing Ca²⁺ release from SR
   • Preparation: Each vial = 20 mg dantrolene + 3g mannitol in 60 mL sterile water (difficult to reconstitute — need multiple personnel)
   • Dantrolene nanosuspension (Ryanodex): 250 mg/vial — reconstitutes rapidly in 5 mL

• Cooling: Ice packs to axilla/groin/head, IV cold saline (10 mL/kg × 3 boluses), cooling blanket; stop cooling at 38.5°C
• Treat hyperkalaemia: Calcium gluconate IV, insulin + dextrose, NaHCO₃ (if metabolic acidosis)
• Treat acidosis: Sodium bicarbonate (if pH <7.2)
• Arrhythmias: If VT/VF — cardiovert; do NOT use calcium channel blockers (CCB) with dantrolene (risk of hyperkalemia + cardiac arrest)
• Urine output: Maintain >1 mL/kg/hr with IV fluids; Furosemide if needed (prevent renal failure from myoglobinuria)
• Catheterise: Urine output monitoring essential

• ABG, electrolytes, CK, coagulation (DIC screen), urine myoglobin
• Core temperature (oesophageal/rectal/bladder)
• ECG continuous

• ICU monitoring for 24–48 hrs
• Dantrolene 1 mg/kg IV 4-hourly for 24h (to prevent recurrence)
• Genetic counselling + RYR1 mutation testing for patient and family
• Caffeine-halothane contracture test (CHCT) for susceptibility testing
• MHAUS hotline: 1-800-MH-HYPER

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B. Compartment Syndrome (as relevant in TKR/tourniquet context)

• Prolonged tourniquet use (>90 min), tourniquet pressure too high
• Tight cast/bandage post-surgery
• Reperfusion injury post-tourniquet
• Trauma, fractures

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