Anaesthesia for Coronary Artery Bypass Grafting

Quick Answer

Coronary artery bypass grafting (CABG) requires myocardial protection during ischemic arrest, hemodynamic optimization, and management of bleeding/coagulopathy. Preoperative: Continue antiplatelet agents (aspirin), stop warfarin/DOACs, beta-blockers continued. Monitoring: Arterial line, central line, TEE, urinary catheter, temperature. Induction: Etomidate or ketamine (hemodynamic stability), high-dose opioid (fentanyl 10-20 μg/kg or remifentanil), avoid hypotension. Cardiopulmonary bypass: Systemic cooling (28-34°C), cardioplegia (antegrade ± retrograde), target MAP 50-70 mmHg. Off-pump CABG: Heparin 300-400 IU/kg (ACT >400 seconds), haemodynamic manipulation (Trendelenburg, rotation), avoid hypotension, conversion to on-pump if unstable. Post-bypass: Check graft flow, manage bleeding (tranexamic acid, cell salvage, blood products), rate/rhythm control, inotropes if needed. [1-10]

Pathophysiology

Coronary Artery Disease

Pathophysiology:

• Atherosclerotic plaque: Obstruction to coronary blood flow
• Stable angina: Fixed stenosis → supply-demand mismatch
• Unstable angina/NSTEMI: Plaque rupture, thrombosis, incomplete occlusion
• STEMI: Complete occlusion, myocardial necrosis
• LV dysfunction: Ischemia/infarction → regional/global hypokinesis

Surgical Indications:

• Left main disease: >50% stenosis
• Triple vessel disease: Especially with diabetes or LV dysfunction
• Failed PCI: Restenosis, complex lesions
• STEMI: Emergency CABG (mechanical complications, failed PCI)
• SYNTAX score: High scores favour surgery over PCI

Conduit Options:

1. Left Internal Mammary Artery (LIMA):

• Preferred: To left anterior descending (LAD)
• Advantages: 10-year patency >90%, survival benefit
• Disadvantages: Single artery (flow limited), spasm risk
• Harvest: Pedicled (with surrounding tissue) or skeletonized

2. Radial Artery:

• Use: Second choice after LIMA
• Advantages: Good patency (80-85% at 5 years), versatile
• Disadvantages: Spasm risk (requires calcium channel blockers), smaller diameter
• Assessment: Allen test (collateral flow), ultrasound

3. Saphenous Vein Grafts (SVG):

• Use: Multiple grafts, distal targets
• Advantages: Abundant, easy harvest
• Disadvantages: Lower patency (50-60% at 10 years), atherosclerosis prone
• Harvest: Open or endoscopic

4. Right Gastroepiploic Artery:

• Use: Inferior wall targets
• Rarely used: Technical difficulty, limited reach

Myocardial Protection

Purpose:

• Protect heart during ischemic arrest (cross-clamp period)
• Minimize myocardial damage
• Allow complex surgery with prolonged cross-clamp times

Cardioplegia:

• High potassium (10-30 mmol/L): Depolarizes myocardium, arrests in diastole
• Hypothermia (4-10°C): Reduces metabolic demand
• Oxygen: Blood cardioplegia (preferred) or crystalloid

Delivery Methods:

1. Antegrade: Aortic root or direct coronary ostia
   • Easy, effective for anterior territory
   • Less effective in occluded/distal territories
2. Retrograde: Coronary sinus
   • Good for distal/territories supplied by occluded vessels
   • Better right heart protection
   • Balloon catheter prevents excessive pressure
3. Combined: Antegrade + retrograde (optimal)

Dosing:

• Initial: 10-15 mL/kg (800-1200 mL)
• Maintenance: Every 20-30 minutes or continuous
• Hot shot: Warm blood cardioplegia just before cross-clamp removal (reperfusion, metabolic recovery)

Additional Protection:

• Systemic hypothermia: 28-34°C (reduces metabolic demand)
• Topical cooling: Saline slush in pericardium
• LV venting: Prevents distension, subendocardial ischemia

Off-Pump CABG (OPCAB)

Technique:

• Surgery on beating heart without CPB
• Stabilizer devices (suction/pressure) immobilize target area
• Snares/occluders isolate coronary artery

Advantages:

• Avoids CPB-related complications (inflammation, coagulopathy, air embolism)
• Reduced transfusion requirements
• Earlier extubation
• Lower cost

Disadvantages:

• Technically more difficult (moving target)
• Incomplete revascularization possible
• Conversion to on-pump (1-5%)
• Steep learning curve

Patient Selection:

• Good candidates: Good LV function, accessible targets (anterior, lateral), no severe comorbidity
• Poor candidates: Poor LV function, dilated heart, intramyocardial vessels, unstable hemodynamics, emergency surgery

Haemodynamic Management:

• Trendelenburg position: Improves venous return during lateral wall exposure
• Rightward rotation: For lateral/posterior targets
• Avoid hypotension: MAP >70 mmHg (critical for coronary perfusion)
• Inotropes: Frequently needed during displacement

Clinical Presentation

Preoperative Assessment

History:

• Angina: Frequency, severity, pattern (stable vs. unstable)
• MI history: Number, location, complications (LV aneurysm, VSD, MR)
• Heart failure: NYHA class, ejection fraction
• Risk factors: Diabetes, hypertension, smoking, hyperlipidemia, family history
• Previous PCI: Stents (drug-eluting vs. bare metal), complications
• Comorbidities: Stroke, renal dysfunction, peripheral vascular disease, COPD
• Medications: Antiplatelets, anticoagulants, beta-blockers, statins

Physical Examination:

• Cardiovascular: Murmurs (MR, AS), gallop (S3), JVP elevation, peripheral edema
• Vascular: Peripheral pulses (femoral for IABP access), carotid bruits
• Respiratory: Baseline status, signs of failure
• Neurological: Baseline cognitive function

Investigations:

• Coronary angiography: Anatomy, severity, target vessels
• Echocardiography: LV function (EF), wall motion, valvular disease, MR severity
• Carotid Doppler: If bruits or history of stroke/TIA (>70% stenosis → consider endarterectomy)
• Blood work: FBC, coagulation, creatinine, electrolytes, LFTs
• ECG: Baseline, ischemic changes
• CXR: Cardiomegaly, pulmonary congestion

Risk Stratification:

• EuroSCORE II: Predicts mortality (<2% low risk, 2-5% moderate, >5% high risk)
• STS Score: American alternative
• Risk factors: Age, female, EF <30%, emergency surgery, reoperation, renal failure, COPD, PVD

Medication Management

Continue:

• Aspirin: Continue (reduces mortality, graft patency benefit)
• Beta-blockers: Continue (reduces ischemia, arrhythmias)
• Statins: Continue (inflammation reduction)
• Nitrates: Continue if symptomatic

Stop/Modify:

• Warfarin: Stop 5 days preop (target INR <1.5), bridge with heparin if high risk
• DOACs: Stop per specific agent timing
• Clopidogrel: Stop 5 days preop if elective (bleeding risk), continue if recent stent (<12 months for DES, <1 month for BMS)
• Metformin: Stop day of surgery (lactic acidosis risk if renal impairment)
• ACE inhibitors/ARBs: Controversial (some stop day before due to vasoplegia risk, others continue)

Special Considerations:

• Recent stent: Dual antiplatelet therapy (DAPT) must continue (stent thrombosis risk > bleeding risk)
• Urgent surgery on DAPT: Accept higher bleeding risk, use cell salvage, consider platelet transfusion if excessive bleeding
• Radial artery graft: Calcium channel blockers started preoperatively (prevent spasm)

Management

Anaesthetic Technique

Goals:

1. Hemodynamic stability (avoid ischemia)
2. Myocardial protection (during CPB)
3. Early extubation (fast-track when appropriate)
4. Pain management (multimodal)

Premedication:

• Avoid heavy sedation: Respiratory depression, hypotension
• Consider: Midazolam 1-2 mg (anxiolysis without respiratory compromise)
• Pre-emptive analgesia: Paracetamol 1 g PO/IV, gabapentin 300-600 mg PO (reduces opioid requirements)

Monitoring:

• Standard: ECG (lead II and V5 for ischemia), SpO₂, NIBP
• Arterial line: Pre-induction (beat-to-beat BP)
• Central venous catheter: CVP, drug administration, PA catheter if indicated
• PA catheter: Consider if EF <30%, RV dysfunction, severe MR, complex surgery
• TEE: Essential (wall motion, filling, air detection, valve function)
• Temperature: Nasopharyngeal + bladder
• BIS: Depth monitoring (target 40-60)
• Urinary catheter: Fluid balance

Induction:

• Strategy: Maintain hemodynamic stability, avoid ischemia triggers (tachycardia, hypotension)
• Pre-oxygenation: 100% O₂ for 3-5 minutes
• Etomidate: 0.2-0.3 mg/kg (hemodynamically neutral, good for ischemic disease)
• Alternative: Ketamine 1-2 mg/kg (sympathomimetic, maintains BP)
• Cautious: Propofol 0.5-1 mg/kg (if used, slowly titrated - vasodilation/myocardial depression)
• Opioid:
  • Fentanyl 10-20 μg/kg or
  • Remifentanil infusion 0.1-0.3 μg/kg/min
• Muscle relaxant: Rocuronium 0.6-1 mg/kg (or suxamethonium if RSI)
• Airway: ETT 8.0-8.5 mm (consider RSI if high aspiration risk)

Maintenance:

• TIVA: Propofol (50-150 μg/kg/min) + remifentanil (0.1-0.2 μg/kg/min)
  • Advantages: ↓Cerebral metabolism, early extubation
• Volatile: Sevoflurane 0.5-1 MAC + remifentanil
  • Advantages: Preconditioning effect (cardioprotective)
• Propofol vs. volatile: Evidence mixed, institutional preference varies
• BIS: 40-60 (adequate depth, prevents awareness)

Pre-Bypass Management:

• Hemodynamics: Target HR 60-80 bpm, avoid hypotension (MAP >70 mmHg for coronary perfusion)
• Anticoagulation: Heparin 300-400 IU/kg (target ACT >480 seconds)
• Sternotomy: Ensure adequate depth before incision
• Internal mammary harvest: Watch for bradycardia (sternal traction), hypotension (mediastinal manipulation)

Cardiopulmonary Bypass

Cannulation:

• Arterial: Ascending aorta (most common), femoral (redo/minimally invasive)
• Venous: Single two-stage right atrial or bicaval
• Cardioplegia: Antegrade (aortic root) ± retrograde (coronary sinus)

Initiation:

1. ACT >480 seconds confirmed
2. Venous drainage established
3. Arterial flow started (gradual increase)
4. Target flow: 2.0-2.4 L/min/m²
5. Cooling initiated (if planned)
6. Aortic cross-clamp applied
7. Cardioplegia delivered (initial dose 10-15 mL/kg)

Bypass Management:

• MAP: 50-70 mmHg (higher if cerebrovascular disease, lower if aortic surgery)
• Flow: 2.0-2.4 L/min/m² (adjust for temperature, hematocrit)
• Temperature: 28-34°C (mild-moderate hypothermia for myocardial protection)
• Cardioplegia: Maintenance doses every 20-30 min or continuous
• Ventilation: Discontinue during bypass (reduces lung injury)
• Laboratory: ABG, electrolytes, Hb q30-60 min
• Glucose: Maintain 6-10 mmol/L (insulin if needed)

Rewarming:

• Gradual to 36-37°C
• Watch for air embolism (gas solubility changes)
• Ensure adequate flow before weaning

Weaning from Bypass

Preparation:

1. Rewarming: Complete to 36-37°C
2. Defibrillation: If VF, cardiovert (10-20 J internal paddles)
3. Rhythm: Ensure stable (pacing if needed)
4. Ventilation: Resume (protective strategy: low tidal volume 6-8 mL/kg)
5. De-airing: TEE-guided maneuvers (Trendelenburg, lung inflation)
6. Inotropes: Prepared (dobutamine, milrinone, adrenaline)

Weaning Sequence:

1. Partial bypass (reduce flow to 50-70%)
2. Assess LV function on TEE
3. If stable, remove aortic cannula
4. Trial off (clamp venous line)
5. If stable, remove venous cannula
6. Protamine (1 mg per 100 IU heparin)
7. Hemostasis assessment

Failure to Wean:

• Causes: Poor myocardial protection, incomplete revascularization, air embolism, graft failure
• Management: Re-establish bypass, inotropes, IABP, re-examine grafts

Post-Bypass Management

Hemodynamics:

• MAP: 70-80 mmHg (perfusion pressure for grafts)
• Heart rate: 60-80 bpm (avoid tachycardia - increases O₂ demand)
• Rhythm: Sinus preferred (atrial pacing if needed)
• Inotropes: Tailored to LV function
  • Good LV: Minimal/none
  • Poor LV: Dobutamine + milrinone ± adrenaline
  • RV failure: Milrinone, inhaled NO

Bleeding Management:

1. Surgical: Check anastomoses, suture lines
2. Medical:
   • Tranexamic acid: 1 g IV (if not given), antifibrinolytic
   • Protamine: Ensure complete heparin reversal
   • Fibrinogen: If <2 g/L (cryoprecipitate or concentrate)
   • Platelets: If <100 × 10⁹/L or dysfunction
   • FFP: If coagulopathy (dilutional)
   • Recombinant Factor VIIa: Last resort (prothrombotic)
3. Cell salvage: Autotransfusion (up to 50% of shed blood)

Re-exploration Criteria:

• Chest tube output >200 mL/hour × 2 hours

• 500 mL in first hour

• Tamponade physiology
• Cardiac arrest with suspected tamponade

Extubation:

• Fast-track: 2-6 hours post-surgery (appropriate candidates)
• Criteria:
  • Awake, following commands
  • Hemodynamically stable (minimal inotropes)
  • Normothermic
  • Adequate ventilation (SpO₂ >95% on 40% FiO₂, acceptable ABG)
  • Minimal bleeding
• Delayed extubation: High-risk patients (poor LV, reoperation, long CPB, complications)

Pain Management

Multimodal Strategy:

1. Paracetamol: 1 g q6h IV/PO (reduce opioid requirements 20-30%)
2. NSAIDs: Celecoxib 200 mg BD (if no renal failure, bleeding concern)
3. Gabapentinoids: Pregabalin 75 mg BD or gabapentin 300 mg TDS
4. Opioids:
   • Morphine PCA (1 mg bolus, 5-10 min lockout) or
   • Fentanyl infusion (1-2 μg/kg/hour) transitioning to oral
5. Regional:
   • SAP block (serratus anterior plane) - bilateral for sternotomy
   • ESP block (erector spinae plane)
   • Local infiltration by surgeon

Specific Considerations:

• Epidural: Rarely used (anticoagulation concerns)
• Thoracic paravertebral: Alternative for sternotomy pain
• Non-opioid priority: Reduce opioid-related complications (nausea, ileus, respiratory depression)

Indigenous Health Considerations

Aboriginal and Torres Strait Islander Patients

Cardiovascular Risk:

• Higher prevalence: IHD presents earlier, more severe
• Risk factors: Higher rates of diabetes, hypertension, smoking, renal disease
• Access issues: Delayed presentation, geographic barriers to cardiac surgical centres

Rheumatic Heart Disease:

• Some CABG patients may have co-existing valve disease from RHD
• Requires combined procedure planning

Postoperative Care:

• Discharge planning: Challenges with remote follow-up (cardiac rehabilitation)
• Medication adherence: Complex regimens (antiplatelets, statins, beta-blockers)
• Secondary prevention: Address modifiable risk factors (smoking cessation, diabetes control)
• Cultural support: Aboriginal liaison officers, family involvement

Māori Health Considerations

Health Disparities:

• Higher cardiovascular mortality
• Earlier onset of IHD
• Higher rates of diabetes and smoking

Cultural Safety:

• Whānau involvement: Family support for major cardiac surgery
• Communication: Clear explanations, allowing time for questions
• Postoperative: Coordination with primary care for ongoing management
• Cardiac rehabilitation: Culturally appropriate programmes

ANZCA Final Exam Focus

SAQ Patterns

Common Questions:

• "Describe the anaesthetic management for on-pump CABG."
• "Compare on-pump versus off-pump CABG from an anaesthetic perspective."
• "How would you manage a patient who cannot be weaned from cardiopulmonary bypass?"
• "What strategies are used for myocardial protection during CABG?"

Marking Scheme Priorities:

• Preoperative optimization (antiplatelet/anticoagulation management)
• Induction strategy (hemodynamic stability)
• CPB management (flow, pressure, temperature)
• Myocardial protection (cardioplegia techniques)
• Weaning from bypass (inotropes, pacing, TEE)
• Postoperative bleeding management (algorithm)

Viva Scenarios

Scenario 1: Failed Weaning from Bypass

• TEE assessment (new wall motion abnormality)
• Inotrope strategy (dobutamine + milrinone)
• IABP indication
• Graft assessment

Scenario 2: Postoperative Bleeding

• Mediastinal drainage interpretation
• Re-exploration criteria
• Blood product management (TXA, fibrinogen, platelets)

Scenario 3: Off-Pump Conversion

• Haemodynamic instability during lateral wall grafting
• Decision to convert to on-pump
• Management of heparin and anticoagulation

Key Points for Examination Success

1. Myocardial protection: Cardioplegia (antegrade ± retrograde), hypothermia
2. Heparin: 300-400 IU/kg, ACT >480 seconds mandatory
3. Bypass targets: Flow 2.0-2.4 L/min/m², MAP 50-70 mmHg
4. Weaning: TEE assessment, inotropes ready, de-airing maneuvers
5. OPCAB: ACT >400 seconds, haemodynamic manipulation (Trendelenburg, rotation), convert if unstable
6. Bleeding: TXA 1 g, cell salvage, blood products per algorithm, re-explore if >200 mL/hour × 2 hours
7. Graft patency: LIMA to LAD (best outcomes), radial artery (second choice), SVG (if needed)
8. Antiplatelets: Continue aspirin through surgery (graft patency benefit)
9. Fast-track: Early extubation when criteria met

References

1. ANZCA. PS54. Statement on Cardiopulmonary Bypass. 2020.
2. Hillis LD et al. 2011 ACCF/AHA Guideline for Coronary Artery Bypass Graft Surgery. Circulation. 2011;124(23):e652-e735.
3. Fihn SD et al. 2012 ACCF/AHA/ACP/AATS/PCNA/SCAI/STS Guideline for the Diagnosis and Management of Patients With Stable Ischemic Heart Disease. Circulation. 2012;126(25):e354-e471.
4. Augoustides JG et al. Anesthesia for cardiac surgery. In: Kaplan's Cardiac Anesthesia. 7th ed. Elsevier; 2017:645-700.
5. Taggart DP et al. Bilateral versus single internal mammary grafts. N Engl J Med. 2019;380(26):2540-2549.
6. Puskas JD et al. Off-pump versus on-pump coronary artery bypass grafting. N Engl J Med. 2021;384(19):1825-1835.
7. ATSI Health. Cardiovascular disease in Aboriginal and Torres Strait Islander peoples. Australian Institute of Health and Welfare; 2021.