1. Off-pump CABG: o Indications o Technique o Advantages/disadvantages 2. Heparin during CPB 3. Cardioplegia 4. Weaning from CPB 5. Complications after CPB and management 6. Common complications after CABG 7. Aortic cross-clamping: o Hemodynamic changes o Metabolic changes o Therapeutic interventions Give answer for dnb anaesthesia exam from millers consise 5 mark 10mark
Reading File
Now let me search the library in parallel for all the topics needed.
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Reading File
Reading File
Finding Sources
Finding Sources
Finding Sources
Reading File
Reading File
Reading File
Reading File
Reading File
Reading File
Reading File
I now have comprehensive content from Miller's Anesthesia and other references. Let me compile the complete DNB exam answers.Here are comprehensive DNB Anaesthesia exam answers drawn from Miller's Anesthesia (10e), Morgan & Mikhail's Clinical Anesthesiology (7e), and Barash's Clinical Anesthesia (9e):
DNB Anaesthesia — Cardiac Anaesthesia: Structured Exam Answers
1. OFF-PUMP CORONARY ARTERY BYPASS GRAFTING (OPCAB)
Indications (5 marks)
OPCAB (also called beating-heart CABG) is preferred when CPB-related morbidity risk is elevated:
| Category | Specific Indications |
|---|---|
| Aortic disease | Severe ascending aortic calcification ("porcelain aorta"), mobile atheromas on epiaortic echo |
| Neurological risk | Prior stroke, severe cerebrovascular disease, carotid stenosis |
| Renal | Pre-existing chronic kidney disease (reduced AKI risk) |
| Pulmonary | Severe COPD — avoids CPB-related lung injury |
| Haematological | Heparin-induced thrombocytopenia (HIT), jehovah's witnesses (reduces blood use) |
| General high-risk | Elderly patients, redo sternotomy, hepatic dysfunction |
Technique (10 marks)
Positioning & Access: Standard median sternotomy. Surgical table is elevated and rotated.
Stabilization: A tissue stabilizer (e.g., Octopus device) uses suction cups to immobilize the target coronary artery segment while the rest of the heart continues to beat.
Verticalization: The Maquet access device uses suction to displace and rotate the heart to expose lateral and posterior vessels (circumflex system). This maneuver causes:
- Reduced LV filling → ↓ CO
- Increased mitral regurgitation
- Kinking of great vessels → arrhythmias
Sequence of anastomoses: LIMA to LAD is usually performed first (easiest and most critical). Subsequent grafts to lateral/posterior walls are more hemodynamically challenging.
Intracoronary shunts: Small flexible shunts are inserted into the coronary artery lumen to maintain distal perfusion during anastomosis.
Anaesthetic management:
- 5-lead ECG + invasive arterial line mandatory
- TEE — midesophageal view preferred (transgastric limited during verticalization)
- Intravascular volume loading + Trendelenburg position to counteract ↓ preload
- Vasoconstrictors (phenylephrine or norepinephrine) for hypotension
- Heparin administered before IMA pedicle clamping (full anticoagulation maintained)
- Emergency conversion to on-pump CPB (~3% of cases) — requires immediate availability of femoral cannulation
Conversion triggers: Persistent ECG changes, haemodynamic collapse, inability to achieve adequate exposure.
Advantages and Disadvantages (5 marks)
| Advantages | Disadvantages |
|---|---|
| Avoids CPB-related systemic inflammatory response | Technically demanding; limited exposure to posterior vessels |
| ↓ Neurological complications (no aortic manipulation) | Haemodynamic instability during heart manipulation |
| ↓ Blood transfusion requirements | Emergency conversion associated with ↑ mortality, stroke, renal failure |
| ↓ AKI incidence (some evidence) | Graft patency rates may be lower (higher redo revascularization rate ~93.6% vs 89.9%) |
| ↓ ICU and hospital stay | Limited TEE views during verticalization |
| Preferred in porcelain aorta / HIT | No definitive mortality benefit over on-pump CABG in RCTs (ROOBY trial) |
— Miller's Anesthesia 10e, Chapter 50; Morgan & Mikhail 7e, Chapter 21
2. HEPARIN DURING CARDIOPULMONARY BYPASS
(10 marks)
Rationale
Contact of blood with the non-endothelial surfaces of the CPB circuit activates the coagulation cascade. Unfractionated heparin (UFH) is the standard anticoagulant because it is rapid-acting, titratable, and fully reversible with protamine.
Mechanism
Heparin binds antithrombin III → 1000× acceleration of antithrombin's inhibition of thrombin (IIa) and factor Xa. It prevents thrombus formation within the circuit.
Dosing Protocol
| Step | Detail |
|---|---|
| Initial dose | 300–400 units/kg IV (bolus) before aortic cannulation |
| Target ACT | ≥ 400–480 seconds before initiating CPB |
| Maintenance | Additional heparin boluses guided by repeated ACT measurements (every 30 min during CPB) |
| Monitoring | Activated Clotting Time (ACT) — point-of-care test; target > 480 s during CPB |
Heparin Resistance
Some patients (antithrombin III deficiency, prior heparin exposure, thrombocytosis) require large doses to achieve target ACT. Treatment: fresh frozen plasma (as antithrombin III source) or recombinant antithrombin III concentrate.
Reversal with Protamine
- Administered after decannulation
- Dose: 1–1.3 mg protamine per 100 units of heparin in circulation
- Infused slowly over 5–10 minutes (rapid infusion → hypotension, pulmonary hypertension, anaphylaxis)
- ACT should return to baseline after protamine
- Protamine must NOT enter the CPB circuit (will clot residual blood)
Special Situation: Heparin-Induced Thrombocytopenia (HIT)
- Heparin is absolutely contraindicated
- Alternatives for CPB anticoagulation:
- Bivalirudin (direct thrombin inhibitor) — most commonly used
- Argatroban
- Fondaparinux (limited evidence for CPB)
- Preoperative plasmapheresis to remove HIT antibodies, then heparin, if no alternative available
- No agent is currently definitively approved for CPB anticoagulation in HIT
— Miller's Anesthesia 10e, Chapter 50; Goodman & Gilman's Pharmacology
3. CARDIOPLEGIA
(10 marks)
Purpose
Cardioplegia provides controlled, reversible cardiac arrest to create a still, bloodless surgical field and protect the myocardium from ischemic injury during aortic cross-clamping.
Mechanism of Arrest
- High extracellular potassium (10–40 mEq/L) reduces transmembrane resting potential → diastolic arrest
- Cold temperature reduces metabolic demand (↓ O₂ consumption ~97% at 10–15°C)
Composition of Cardioplegic Solution
| Component | Purpose | Amount |
|---|---|---|
| Potassium | Arrest (membrane depolarization) | 10–40 mEq/L |
| Sodium | Below plasma levels (<140 mEq/L) | ↓ intracellular Na⁺ accumulation |
| Calcium | Cellular integrity | 0.7–1.2 mmol/L |
| Magnesium | Blocks Ca²⁺ influx | 1.5–15 mmol/L |
| Buffer (HCO₃⁻, histidine, THAM) | Prevent acidosis | Alkalotic pH preferred |
| Mannitol | Control cellular oedema | Added as osmotic agent |
| Lidocaine/glucocorticoids | Membrane stabilization | Optional |
| Glucose, glutamate, aspartate | Energy substrates | Added |
Crystalloid vs. Blood Cardioplegia
- Blood cardioplegia (4:1 blood:crystalloid) is standard in North America — provides O₂ delivery, antioxidants, buffers
- Oxygenated blood cardioplegia has more O₂ than crystalloid; beneficial in high-risk patients
Routes of Delivery
| Route | Description |
|---|---|
| Antegrade | Catheter in proximal aortic root (between cross-clamp and aortic valve) → coronary ostia |
| Retrograde | Catheter via right atrium into coronary sinus → retrograde through venous system |
| Combined | Antegrade + retrograde shown superior at some centers — ensures delivery to areas distal to coronary obstructions |
Temperature
- Cold cardioplegia (4–10°C): most common; reduces metabolic rate; must be repeated ~every 30 min (washout + rewarming from ambient air and aorta)
- Warm/tepid cardioplegia: provides metabolic support; continuous delivery needed; limits "dry" surgical field
- Normothermic CPB: concerns about losing hypothermic neuroprotection
Complications of Inadequate Cardioplegia
- Ventricular fibrillation → ↑ O₂ demand
- Ventricular distension → subendocardial ischaemia
- Air embolism (coronary or cerebral) during de-airing
— Morgan & Mikhail 7e, Chapter 21; Miller's Anesthesia 10e, Chapter 50
4. WEANING FROM CARDIOPULMONARY BYPASS
(10 marks)
Prerequisites — the "CVP" Mnemonic (Morris et al.)
C — Cold (Temperature)
- Nasopharyngeal and venous blood temperature: 36–37°C before weaning
- Hyperthermia (>37°C) increases risk of neurological complications
C — Conduction (Cardiac Rate & Rhythm)
- Target heart rate: 80–100 beats/min
- Bradycardia: epicardial pacing wires ± β-adrenergic chronotropic drugs
- Tachycardia (>120): treat cause (anaemia, hypovolaemia, "light" anaesthesia)
- 3rd degree AV block: AV sequential pacing
- SVT: synchronized cardioversion; amiodarone/esmolol/verapamil/adenosine
- Sinus rhythm preferred (especially with poor LV compliance — "atrial kick" essential)
V — Ventilation
- Lungs must be re-inflated and ventilated before weaning
- Confirm bilateral air entry, adequate gas exchange
P — Perfusion (Pressures, Pump function, Pharmacology)
- Check and correct electrolytes — potassium critical (target 4.0–4.5 mEq/L; hypokalaemia → arrhythmias)
- Confirm adequate preload
- Assess LV function with TEE
- Inotropes (dopamine, dobutamine, epinephrine, milrinone) prepared if needed
- Vasopressors (norepinephrine, vasopressin) for vasoplegic syndrome
Procedure
- Perfusionist gradually reduces venous drainage to the CPB circuit, allowing progressive cardiac filling
- Arterial pump flow decreased as cardiac output increases
- Ventilation resumed (confirm bilateral equal air entry)
- TEE used to confirm: de-airing of LV, adequate filling, wall motion, valvular function
- CPB flow reduced to zero when haemodynamics stable
- Decannulation after haemostasis confirmed
- Protamine administered slowly (1–1.3 mg/100 units heparin) after all cannulae removed
Difficulty Weaning — Low Cardiac Output Syndrome (LCOS)
Definition: Haemodynamic instability requiring inotropes, IABP, or ECMO
Causes: Poor myocardial protection, incomplete revascularisation, ischaemia, air embolism, valvular dysfunction, RV failure
Management stepladder:
- Optimize preload (TEE-guided volume)
- Optimize rate and rhythm (pacing)
- Inotropes: dobutamine, dopamine, milrinone (PDE-III inhibitor — ↑ cAMP, inotropy + vasodilation)
- Vasopressors: norepinephrine, vasopressin
- Mechanical support: IABP (↓ afterload + ↑ diastolic coronary perfusion)
- Ventricular assist device (VAD) or ECMO
— Miller's Anesthesia 10e, Chapter 50 (Table 50.3); Barash 9e, Chapter 28
5. COMPLICATIONS AFTER CPB AND MANAGEMENT
(10 marks)
A. Neurological Complications
| Complication | Cause | Management |
|---|---|---|
| Stroke / cerebral embolism | Aortic atheroembolism, air embolism, hypoperfusion | Epiaortic echo to locate plaque; optimize perfusion pressure; de-airing protocol |
| Cognitive dysfunction (POCD) | Microemboli, inflammation, hypoperfusion | Optimize pump flow, pulsatile flow, arterial filtration, avoid hyperthermia |
B. Cardiac Complications
| Complication | Features | Management |
|---|---|---|
| Low cardiac output syndrome | CI <2.2 L/min/m², oliguria, hypotension | Inotropes, IABP, ECMO (see above) |
| Perioperative MI | New RWMA on TEE, ST changes, troponin rise | Revascularization (percutaneous or surgical), IABP, anticoagulation |
| Arrhythmias | AF most common post-CABG (~30%) | Amiodarone, beta blockers, DC cardioversion |
| Cardiac tamponade | Post-op bleeding, haemodynamic collapse | Emergency re-exploration; pericardiocentesis temporising |
| Vasoplegia syndrome | ↓ SVR, refractory hypotension, normal/high CO | Norepinephrine, vasopressin, methylene blue (iNOS inhibitor) |
C. Pulmonary Complications
- ALI/ARDS: CPB activates complement → neutrophil sequestration in lungs → ↑ permeability
- Atelectasis/pneumonia: Post-sternotomy, prolonged ventilation
- Management: Lung-protective ventilation (Vt 6 ml/kg, PEEP), early extubation protocol
D. Renal Complications
- AKI: Incidence ~5–30%; caused by ↓ renal perfusion, microemboli, haemolysis, inflammatory mediators
- Risk factors: Pre-existing CKD, prolonged CPB, ↓ mean perfusion pressure, off-pump conversion
- Management: Optimize perfusion pressure (MAP >70 mmHg during CPB), avoid nephrotoxins, renal replacement therapy if oliguric AKI
E. Haematological / Bleeding Complications
- Causes: Dilutional coagulopathy, platelet dysfunction, heparin rebound, hypothermia-induced coagulation defects, fibrinolysis
- Chest tube drainage >250–300 mL/h (first 2h) → surgical re-exploration
- Management: Protamine, FFP, platelets, cryoprecipitate, antifibrinolytics (tranexamic acid), cell salvage; TEG/ROTEM-guided therapy
- Cardiac tamponade from inadequately drained bleeding → emergency chest reopening
F. Gastrointestinal Complications
- Mesenteric ischaemia (splanchnic hypoperfusion during CPB), pancreatitis, GI bleeding
- Management: Early recognition, supportive care, surgical intervention if ischaemia
G. Systemic Inflammatory Response Syndrome (SIRS)
- Caused by blood–foreign surface contact, ischaemia-reperfusion injury, endotoxaemia
- Manifests as fever, ↓ SVR, multi-organ dysfunction
- Management: Steroids (controversial), ultrafiltration, modified circuits (heparin-bonded)
— Miller's Anesthesia 10e, Chapters 50, 51; Morgan & Mikhail 7e
6. COMMON COMPLICATIONS AFTER CABG
(5–10 marks)
Ischaemia/Graft Failure
- Causes: Poor anastomosis quality, graft kinking (too long → kink; too short → stretch), graft thrombosis, coronary spasm, incomplete revascularisation, air/atheroembolism to grafts
- Diagnosis: New RWMA on TEE, ST changes, haemodynamic deterioration
- Management:
- Nitroglycerin (↑ coronary flow, ↓ preload)
- Calcium channel blocker (diltiazem) for coronary spasm
- Phenylephrine to "push" air through coronary if air embolism
- Beta-blockers (atenolol) to ↓ HR and O₂ demand
- IABP for refractory ischaemia
- Emergency surgical revision or reinstitution of CPB
Arrhythmias
- Atrial fibrillation: Commonest (~25–40%) — begins day 2–4 post-op; management: amiodarone (first-line), beta-blockers, cardioversion if haemodynamically unstable
- Ventricular arrhythmias: Often ischaemia-related; amiodarone, lidocaine, defibrillation
Neurological
- Stroke (~1–2%): aortic manipulation, air/particulate emboli, hypoperfusion
- Delirium: Very common post-cardiac surgery; managed with reorientation, haloperidol, dexmedetomidine
Respiratory
- Prolonged mechanical ventilation (especially with LV dysfunction)
- Pleural effusion (especially left-sided — from IMA harvesting)
- Phrenic nerve palsy (from cold cardioplegia or IMA harvesting)
Chest Closure Complications
- Hypotension during chest closure: Due to hypovolaemia, graft kinking, myocardial oedema compressing RV
- TEE is key diagnostic tool
- Reopen sternum if refractory
Wound Complications
- Sternal dehiscence/mediastinitis (~1–2%): especially in diabetics, obese, bilateral IMA harvesting
- Deep sternal wound infection — requires debridement, flap reconstruction
Renal
- Post-op AKI: especially if prolonged pump time, pre-existing CKD
Bleeding / Cardiac Tamponade
- Inadequate haemostasis → tamponade → ↑ CVP, ↓ CO, pulsus paradoxus
- Emergency re-exploration
— Miller's Anesthesia 10e, Chapter 50
7. AORTIC CROSS-CLAMPING
(10 marks)
A. Haemodynamic Changes
On Application of Cross-Clamp
| Parameter | Change | Mechanism |
|---|---|---|
| Afterload (SVR) | ↑↑ markedly | Outflow obstruction above clamp level |
| Mean arterial pressure | ↑ (proximal hypertension) | ↑ impedance to LV ejection |
| LV wall stress | ↑ | Laplace's law |
| LV end-diastolic pressure | ↑ | Diastolic dysfunction |
| Cardiac output | ↓ (if myocardium cannot compensate) | ↑ afterload; potential LV failure |
| Preload | ↑ initially | Venous blood volume redistributed proximally from below clamp |
| HR | Reflex bradycardia or tachycardia | Variable |
- Supraceliac clamp: Most haemodynamically severe — splanchnic blood redistributed proximally → ↑ preload and afterload
- Infraceliac clamp: Splanchnic bed can accommodate blood shift; less preload increase
On Release of Cross-Clamp (Most Critical Period)
| Parameter | Change | Mechanism |
|---|---|---|
| SVR | ↓↓ (up to 80%) | Vasoactive/inflammatory mediator release; reactive hyperemia |
| MAP | ↓↓ (profound hypotension) | Afterload collapse + relative hypovolaemia |
| Cardiac output | ↓ | Cardiodepressant metabolites, myocardial stunning |
| Venous return | ↓ | Blood pools in previously ischaemic distal tissues |
| pH | ↓ (acidosis) | Release of lactic acid from ischaemic limbs |
B. Metabolic Changes
During Cross-Clamp (Ischaemia Below Clamp)
- Anaerobic metabolism in ischaemic tissues → lactic acid accumulation
- Intracellular Ca²⁺ overload: failure of Na⁺/Ca²⁺ exchanger → ischaemic cellular injury
- ATP depletion: Na⁺/K⁺-ATPase failure → cell swelling
- Reactive oxygen species accumulate (substrate for reperfusion injury)
- Intracellular acidosis
On Reperfusion (Clamp Release)
- Reperfusion injury: sudden reintroduction of O₂ → ROS burst → lipid peroxidation, cell membrane damage
- Hyperkalaemia: K⁺ efflux from ischaemic cells
- Metabolic acidosis: washout of accumulated H⁺ and lactate into systemic circulation
- Myocardial depression: systemic acidosis + cardiodepressant metabolites
C. Therapeutic Interventions
Before Cross-Clamp Application
- Esmolol IV: ↓ HR to 60–65 bpm → ↓ myocardial O₂ demand
- Vasodilators (sodium nitroprusside, nitroglycerin, nicardipine): offset ↑ afterload and wall stress
- Thoracic epidural: systemic vasodilation and analgesia (also ↓ SVR above clamp)
- Deepening anaesthetic depth
During Cross-Clamp (Maintaining Distal Perfusion)
- Maintain MAP distal to clamp (especially spinal cord perfusion pressure): cerebrospinal fluid (CSF) drainage to ↓ intrathecal pressure
- Avoid excessive vasopressor use above clamp (worsens distal ischaemia)
- Systemic hypothermia (↓ metabolic requirements)
- Spinal cord protection: CSF drainage, naloxone, steroids (controversial)
At Clamp Release
- Volume loading during cross-clamp period (pre-loading before release)
- Gradual, controlled release of cross-clamp (slow partial release → controlled mediator washout)
- Vasopressors: phenylephrine, norepinephrine for refractory hypotension
- Inotropes: epinephrine or calcium chloride for myocardial depression
- Sodium bicarbonate: correct severe acidosis (pH <7.1)
- ↓ anaesthetic depth before clamp release to blunt vasodilatory drop
- Discontinue epidural infusions in anticipation of hypotension
- Bilateral sequential iliac clamp release (if applicable): staged reperfusion for more controlled haemodynamic response
- For refractory hypotension: temporary reapplication of clamp while resuscitation is instituted
— Barash's Clinical Anesthesia 9e, Chapter 40 (Table 40-2, Fig 40-13, Fig 40-14); Morgan & Mikhail 7e, Chapter 21
Quick Revision Summary Table
| Topic | Key "3-point" Recall |
|---|---|
| OPCAB indications | Porcelain aorta, HIT, severe CKD, prior stroke |
| Cardioplegia arrest | K⁺ 10–40 mEq/L + cold + repeated every 30 min |
| Weaning mnemonic | CVP = Cold, Conduction, Ventilation, Pressures |
| Heparin CPB | 300–400 units/kg → ACT >480s → protamine 1–1.3 mg/100U |
| Aortic clamp on | ↑↑ afterload, proximal hypertension → esmolol + vasodilators |
| Aortic clamp off | ↓↓ SVR, acidosis, hypotension → volume load + vasopressors |
| Post-CABG AF | 25–40%; amiodarone first-line |
*Sources: Miller's Anesthesia 10e (Chapters 50–51), Morgan & Mikhail Clinical Anesthesiology 7e (Chapter 21), Barash Clinical Anesthesia 9e (Chapters 28, 40)*All seven topics are covered in exam-ready format. Here's how to use these answers:
Exam Strategy Tips for DNB
For 5-mark questions — write 3–4 focused points per subheading, use a table if listing multiple items, aim for ~250–300 words.
For 10-mark questions — use all three layers (mechanisms + clinical features + management), include a table, end with a management algorithm or mnemonic, aim for ~500–600 words.
High-yield points the examiner looks for:
- OPCAB — "porcelain aorta" + verticalization hemodynamics + 3% emergency conversion rate
- Heparin CPB — dose 300–400 U/kg, ACT target ≥480s, protamine reversal 1–1.3 mg/100U
- Cardioplegia — K⁺ 10–40 mEq/L diastolic arrest, cold, antegrade + retrograde routes, blood vs crystalloid
- Weaning — CVP mnemonic (Cold 36–37°C, Conduction HR 80–100, Ventilation, Pressures/inotropes)
- CPB complications — SIRS, neurological, renal, haematological + management ladder
- Post-CABG — AF (25–40%, amiodarone), graft ischaemia signs, chest closure hypotension
- Aortic clamp — On: ↑↑ afterload → esmolol + vasodilators; Off: ↓↓ SVR + acidosis → volume + vasopressors + gradual release
This is a shared conversation. Sign in to Orris to start your own chat.