Anaesthesia for Thoracic Aortic Surgery

Quick Answer

Thoracic aortic surgery includes open repair and endovascular (TEVAR) approaches. Open repair requires left heart bypass (partial) or deep hypothermic circulatory arrest (DHCA) for arch/proximal descending, with cerebral protection (antegrade cerebral perfusion preferred). Spinal cord protection: Maintain MAP >90 mmHg, CSF drainage (lumbar drain), minimize aortic cross-clamp time, staged repairs, reimplant critical intercostals (T8-L1). TEVAR: Lower spinal cord risk but still present, especially with extensive coverage. Key complications: Paraplegia (5-10% open, 1-3% TEVAR), stroke (5-10%), AKI (20-30%), bleeding. Monitoring: SSEPs/MEPs (spinal cord), EEG (cerebral), double arterial lines (radial + femoral), large-bore IV access, cell salvage essential. Temperature: Moderate hypothermia (28-32°C) or deep (18-20°C) depending on extent. [1-10]

Pathophysiology

Aortic Anatomy and Pathology

Aortic Segments:

1. Root: Aortic valve to coronary arteries
2. Ascending: Coronary ostia to innominate artery
3. Arch: Innominate to left subclavian
4. Descending thoracic: Left subclavian to diaphragm
5. Thoracoabdominal: Diaphragm to renal arteries (Crawford classification)

Indications for Surgery:

• Aneurysm: Diameter >5.5-6 cm ascending, >6-7 cm descending
• Dissection: Acute type A (surgical emergency), complicated type B (rupture, malperfusion)
• Trauma: Aortic transection (isthmus most common)
• Coarctation: Congenital or acquired

Classification Systems:

Crawford Classification (Thoracoabdominal):

• Extent I: Distal arch to above celiac
• Extent II: Distal arch to below renal (most extensive, highest spinal cord risk)
• Extent III: Below 6th rib to below renal
• Extent IV: Below 12th rib to bifurcation

Spinal Cord Blood Supply:

• Anterior spinal artery: Single vessel, vulnerable
• Segmental arteries: Arise from aorta at each level
• Critical region: T8-L1 (artery of Adamkiewicz, largest segmental)
• Collateral flow: Subclavian, hypogastric, intercostals

Open Repair Techniques

Proximal Descending Aorta (Without Circulatory Arrest):

• Left thoracotomy: 4th or 5th intercostal space
• Aortic cross-clamping: Between left subclavian and descending aorta
• Left heart bypass (partial):
  • Left atrium to distal aorta (via centrifugal pump)
  • Flow: 1.5-3 L/min
  • No oxygenator needed
  • Maintains distal perfusion (spinal cord, viscera, kidneys)
  • Reduces afterload on LV

Aortic Arch:

• Median sternotomy or hemi-clamshell
• Deep hypothermic circulatory arrest (DHCA):
  • Temperature: 18-20°C (nasopharyngeal)
  • Duration limit: 30-45 minutes safe
  • pH-stat management (CO₂ added)
• Antegrade cerebral perfusion (ACP):
  • Via brachiocephalic vessels or axillary artery
  • Flow: 10-15 mL/kg/min to each carotid
  • Extends safe DHCA time to 60-90 minutes
• Retrograde cerebral perfusion: Less favored now (embolic risk, inadequate flow)

Thoracoabdominal:

• Left heart bypass or partial CPB
• CSF drainage: Lumbar drain placed preoperatively
• Sequential clamping: Minimize ischemic time
• Intercostal reimplantation: Preserve critical segmentals

Endovascular Repair (TEVAR)

Technique:

• Transfemoral access: Sheath 20-24 Fr
• Stent graft deployment: Under fluoroscopy
• Landing zones: Proximal and distal seal zones >2 cm
• Coverage: Extent determines spinal cord risk

Advantages:

• Less invasive, lower morbidity
• Shorter hospital stay
• Lower early mortality (especially high-risk patients)

Disadvantages:

• Spinal cord ischemia risk (if extensive coverage T8-L1)
• Endoleaks (type I, II, III, IV, V)
• Device migration, fracture
• Access complications (iliac dissection, rupture)
• Not suitable for all anatomy (short necks, tortuosity)

Indications:

• Descending thoracic aneurysm (anatomic criteria)
• Complicated type B dissection
• Traumatic aortic injury
• Coarctation

Contraindications:

• Inadequate landing zones
• Severe tortuosity
• Extensive calcification
• Connective tissue disorders (relative)

Neurological Complications

Spinal Cord Ischemia:

Mechanism:

• Interruption of segmental arteries during aortic clamping
• Hypoperfusion during DHCA
• Hypotension post-repair (steal phenomenon)

Risk Factors:

• Extent II thoracoabdominal (highest risk)
• Previous infrarenal aortic surgery
• Hypogastric artery occlusion
• Prolonged cross-clamp time
• Hypotension postoperatively
• TEVAR covering T8-L1

Prevention:

1. Distal perfusion: Left heart bypass or partial CPB
2. Sequential clamping: Limit ischemic time per segment
3. CSF drainage: Lumbar drain, target pressure 8-12 cm H₂O
4. MAP augmentation: >90 mmHg (higher than normal)
5. Staged repairs: Extensive repairs done in stages
6. Intercostal reimplantation: Critical pairs (T8-L1)
7. MEP/SSEP monitoring: Detect early, intervene
8. Mild hypothermia: 32-34°C (spinal cord protection)

Treatment of Paraplegia:

• Immediate: Increase MAP (vasopressors, fluids), optimize CSF drainage
• Steroids: Methylprednisolone (controversial, some centers use)
• Reoperation: If technical cause identified
• Rehabilitation: Long-term, often permanent deficit

Stroke:

Mechanisms:

• Atheroembolism (arch manipulation)
• Air embolism
• Hypoperfusion (DHCA duration)
• Dissection (malperfusion)

Prevention:

• ACP (antegrade cerebral perfusion)
• pH-stat management (better brain cooling)
• Epiaortic ultrasound (guide cannulation)
• Filtering (arterial line filter)
• Avoid arch atheroma

Risk: 5-10% (higher with arch involvement, age >70, prior stroke)

Recurrent Laryngeal Nerve Injury:

• Left RLN: Wraps under aortic arch, at risk during arch surgery
• Consequence: Vocal cord paralysis (hoarseness, aspiration)
• Incidence: 5-10%

Phrenic Nerve Injury:

• Left hemidiaphragm: Cold injury from topical cooling, dissection
• Consequence: Respiratory compromise

Organ Protection Strategies

Kidneys:

• Risk: AKI in 20-30% (ischemia, contrast, rhabdomyolysis, hemolysis)
• Protection:
  • Minimize contrast (preoperative CTA vs. angiography)
  • Distal perfusion (maintains renal flow)
  • Hydration (isotonic crystalloid)
  • Avoid nephrotoxins
  • Mannitol (osmotic diuretic, free radical scavenger)

Viscera:

• Risk: Mesenteric ischemia, ileus
• Protection: Distal perfusion, sequential clamping

Limbs:

• Risk: Lower extremity ischemia (clamp above celiac)
• Protection: Distal perfusion, femoral-femoral bypass if needed

Clinical Presentation

Preoperative Assessment

History:

• Aetiology: Degenerative, connective tissue disorder (Marfan, Ehlers-Danlos), dissection, trauma
• Symptoms: Pain (back, chest), dysphagia (esophageal compression), hoarseness (RLN), claudication
• Comorbidities: CAD, COPD, renal dysfunction, hypertension
• Previous surgery: Cardiac, aortic, spinal

Physical Examination:

• Cardiovascular: BP differential (arms vs legs if coarctation/dissection), peripheral pulses, bruits
• Neurological: Baseline exam (document for comparison)
• Respiratory: Baseline status (thoracotomy impact)

Investigations:

• Imaging:
  • CTA (anatomy, extent, thrombus, calcification)
  • MRA (no contrast, radiation)
  • Angiography (if endovascular considered)
• Cardiac: Echocardiography (LV function, valvular disease, aortic root), ECG
• Carotid: Doppler if arch surgery (cerebral reserve)
• Pulmonary: Spirometry if COPD
• Laboratory: FBC, coagulation, creatinine, LFTs, type & screen (crossmatch 4-6 units)
• Spinal imaging: MRI if prior spinal surgery (identify critical vessels)

Risk Stratification:

• EuroSCORE II: Predicts mortality
• Risk factors: Age >70, extent II, prior AAA repair, renal dysfunction, COPD, emergency surgery

Specific Considerations

Acute Aortic Dissection:

• Type A: Surgical emergency (mortality 1-2% per hour initially)
• Type B: Medical management unless complicated (rupture, malperfusion, pain uncontrolled)
• Malperfusion: End organ ischemia (coronary, cerebral, mesenteric, renal, limbs)
• Diagnosis: CTA (sensitivity >95%), TEE (bedside, intimal flap, AR)
• Management:
  • BP control (labetalol, esmolol, nitroprusside)
  • Pain control (reduces catecholamines, BP)
  • Surgery: Type A immediately, Type B selectively

Connective Tissue Disorders:

• Marfan syndrome: Fibrillin mutation, aortic root dilation, dissection risk
• Ehlers-Danlos Type IV: Vascular type, tissue fragility (surgery difficult)
• Loeys-Dietz: TGFBR mutation, aggressive aortic disease

Traumatic Aortic Injury:

• Mechanism: Deceleration (MVA, fall)
• Location: Isthmus (90%), mobile arch fixed to descending
• Treatment: TEVAR preferred (lower mortality than open), delayed if stable

Management

Anaesthetic Technique

Preoperative:

• Lumbar drain: Placed preoperatively for CSF drainage (T8 and below surgery)
• Lines: Large bore IVs, arterial lines (radial + femoral for pressure differential), central line, PA catheter if poor LV function
• Premedication: Avoid (if awake for neuro assessment) or cautious midazolam
• Antibiotics: Within 60 minutes (gram-positive coverage)

Monitoring:

• Standard: ECG, SpO₂, EtCO₂, temperature (nasopharyngeal + bladder + skin)
• Arterial lines:
  • Right radial (innominate/left carotid perfusion)
  • Left radial (left subclavian)
  • Femoral (distal perfusion)
• Central venous pressure: Right IJ or subclavian
• PA catheter: If poor LV or RV function
• TEE: Essential (assess cardiac function, aortic pathology, de-airing)
• Neurophysiological monitoring:
  • SSEPs (somatosensory evoked potentials): Posterior column function
  • MEPs (motor evoked potentials): Anterior cord function (more sensitive)
  • EEG: Cerebral activity during DHCA
• CSF pressure: Lumbar drain pressure
• Urine output: Hourly (renal perfusion)
• Cell salvage: Autotransfusion essential

Induction:

• Goals: Hemodynamic stability, avoid hypertension (rupture risk in aneurysm)
• Technique:
  • Etomidate (0.2-0.3 mg/kg): Hemodynamic stability
  • Fentanyl 10-20 μg/kg (blunts pressor response)
  • Rocuronium (avoid suxamethonium after 24-48 hours if prior surgery/burns)
• Airway: ETT (consider double-lumen for left thoracotomy if lung deflation needed)

Maintenance:

• TIVA or balanced: Propofol/sevoflurane acceptable
• Opioids: High dose (fentanyl 20-50 μg/kg or remifentanil infusion)
• Muscle relaxation: Continuous (rocuronium infusion)
• Temperature:
  • Moderate hypothermia (28-32°C) for descending repairs
  • Deep hypothermia (18-20°C) for arch with DHCA

Left Heart Bypass (If Used):

• Cannulation:
  • Inflow: Left atrium (via left superior pulmonary vein or left atrial appendage)
  • Outflow: Distal descending aorta or femoral artery
• Flow: 1.5-3 L/min (based on distal pressure >60 mmHg)
• Anticoagulation: Heparin 100-150 IU/kg (ACT >250-300 seconds)
• No oxygenator: Just pump (centrifugal or roller)

Spinal Cord Protection Protocol:

1. Mild hypothermia: 32-34°C
2. CSF drainage: Lumbar drain, target pressure 8-12 cm H₂O
3. MAP augmentation: Maintain >90 mmHg (higher if cord at risk)
4. MEP/SSEP monitoring: Continuous, alert if changes >50%
5. Intercostal reimplantation: Critical pairs identified by MEP loss during clamping
6. If MEP loss: Increase MAP, optimize CSF drainage, reimplant intercostals, check proximal clamp position

Cerebral Protection (Arch Surgery):

1. pH-stat management: CO₂ added to maintain pH 7.40 (better brain cooling)
2. Antegrade cerebral perfusion:
   • Right axillary artery cannulation with side graft
   • Flow: 10-15 mL/kg/min
   • Target: Pressure 50-70 mmHg in radial artery
3. Temperature: 18-20°C (DHCA)
4. Duration: <45 minutes DHCA alone, <60-90 minutes with ACP
5. Steroids: Methylprednisolone 15 mg/kg (some centers)
6. Barbiturates: Thiopental for burst suppression (if prolonged DHCA)

Postoperative Management

ICU Care:

• Ventilation: Usually 24-48 hours (chest open, fluid resuscitation)
• Hemodynamics:
  • MAP >90 mmHg (spinal cord perfusion) for 48-72 hours
  • Vasopressors often needed (noradrenaline)
  • Avoid hypotension
• CSF drainage: Continue 48-72 hours, wean gradually (occlude 24 hours before removal)
• Spinal cord monitoring: Serial neuro exams (if not paralyzed)
• Renal: Monitor creatinine, urine output (avoid nephrotoxins)

Complications:

1. Paraplegia (5-10% open, 1-3% TEVAR):
   • Immediate assessment
   • Optimize MAP, CSF drainage
   • Imaging (MRI) if delayed onset
2. Stroke (5-10%):
   • Neurological exam q1-2h
   • CT head if deficit
3. AKI (20-30%):
   • Monitor creatinine
   • Supportive care, RRT if needed
4. Bleeding:
   • Mediastinal drainage
   • Coagulopathy correction
   • Re-exploration if >500 mL/hour
5. Respiratory failure:
   • Prolonged ventilation
   • Tracheostomy if needed
6. Endoleak (TEVAR):
   • Type I (proximal/distal leak): Treat (extension cuff)
   • Type II (branch retrograde): Observe often
   • Type III (graft defect): Treat
   • Surveillance imaging (CTA at 1, 6, 12 months)

Indigenous Health Considerations

Aboriginal and Torres Strait Islander Patients

Cardiovascular Risk:

• Higher rates: Hypertension, smoking, renal disease (major risk factors for aneurysms)
• Access issues: Geographic barriers to tertiary aortic surgery centers
• Presentation: May present later with more advanced disease

Rheumatic Heart Disease:

• May have co-existing valve disease requiring combined surgery
• Requires planning for valve replacement if involved

Postoperative Considerations:

• Discharge planning: Challenges with remote follow-up (lifelong surveillance for endovascular)
• Antihypertensive adherence: Critical to prevent aneurysm progression
• Cultural support: Extended hospital stay requires family support

Māori Health Considerations

Health Disparities:

• Higher cardiovascular disease rates
• Earlier onset of hypertension and vascular disease
• Access to specialized vascular and cardiac surgery

Cultural Safety:

• Whānau involvement: Family conferences for treatment planning
• Communication: Clear explanations of complex surgery
• Postoperative care: Coordination with primary care for long-term management
• Rehabilitation: Access to services if spinal cord injury occurs

ANZCA Final Exam Focus

SAQ Patterns

Common Questions:

• "Describe the spinal cord protection strategies during thoracic aortic surgery."
• "How would you manage the anaesthesia for a type A aortic dissection?"
• "Compare open vs. endovascular repair of thoracic aortic aneurysms."
• "What is antegrade cerebral perfusion and when is it used?"

Marking Scheme Priorities:

• Spinal cord protection (CSF drainage, MAP augmentation, MEP/SSEP, mild hypothermia)
• Cerebral protection (pH-stat, ACP, temperature)
• Left heart bypass technique
• Complications (paraplegia, stroke, AKI)
• TEVAR vs. open comparison

Viva Scenarios

Scenario 1: Acute Type A Dissection

• Emergency surgery indication
• BP control (labetalol, nitroprusside)
• Cerebral protection (DHCA, ACP)

Scenario 2: Intraoperative MEP Loss

• Increase MAP >90 mmHg
• Optimize CSF drainage
• Reimplant intercostals
• Extend distal perfusion

Scenario 3: Postoperative Paraplegia

• Optimize spinal cord perfusion (MAP, CSF drainage)
• Imaging to exclude hematoma
• Rehabilitation planning

Key Points for Examination Success

1. Spinal cord protection: MAP >90 mmHg, CSF drainage (8-12 cm H₂O), mild hypothermia 32-34°C, MEP/SSEP monitoring
2. Cerebral protection: pH-stat, antegrade cerebral perfusion 10-15 mL/kg/min, temperature 18-20°C for DHCA
3. Left heart bypass: Left atrium to distal aorta, flow 1.5-3 L/min, ACT >250-300, no oxygenator
4. Paraplegia risk: Extent II highest, TEVAR 1-3%, open 5-10%, staged repairs reduce risk
5. Spinal cord blood supply: T8-L1 critical (Adamkiewicz), collateral from subclavian and hypogastric
6. Double arterial lines: Right radial (innominate/left carotid), femoral (distal)
7. TEVAR: Lower morbidity, spinal cord risk if T8-L1 covered, endoleak surveillance required
8. Risk factors for paraplegia: Prior AAA, hypogastric occlusion, extensive coverage, hypotension

References

1. ANZCA. PS54. Statement on Cardiopulmonary Bypass. 2020.
2. Erbel R et al. 2014 ESC Guidelines on the diagnosis and treatment of aortic diseases. Eur Heart J. 2014;35(41):2873-2926.
3. Hiratzka LF et al. Surgery for aortic dilatation. J Am Coll Cardiol. 2010;55(16):e129-e131.
4. Coselli JS et al. Cerebrospinal fluid drainage and paraplegia. J Vasc Surg. 2007;45(2):375-379.
5. Griepp RB et al. Thoracic aortic surgery. In: Cohn LH (ed). Cardiac Surgery in the Adult. 5th ed. McGraw-Hill; 2017:1245-1272.
6. Preventza O et al. Cerebral protection during aortic arch surgery. J Thorac Cardiovasc Surg. 2018;156(4):1339-1347.
7. Moulakakis KG et al. Open surgery versus endovascular repair. J Vasc Surg. 2019;69(3):e33-e45.
8. ATSI Health. Cardiovascular disease in Aboriginal and Torres Strait Islander peoples. Australian Institute of Health and Welfare; 2021.