Anaesthetic Management for Severe Aortic Stenosis Undergoing AVR
The optimal anaesthetic management for patients with severe aortic stenosis undergoing aortic valve replacement requires strict maintenance of hemodynamic stability with careful attention to maintaining preload, contractility, and sinus rhythm while avoiding tachycardia, hypotension, and increased afterload.
Preoperative Assessment and Preparation
- Confirm AS severity via echocardiography (aortic valve area <1.0 cm², mean gradient ≥40 mmHg, peak velocity ≥4.0 m/s) 1
- Assess for symptoms (dyspnea, angina, syncope) and exercise capacity
- Evaluate left ventricular function, as reduced LVEF (<50%) increases perioperative risk 2
- Review comorbidities that may complicate management (coronary artery disease, hypertension, arrhythmias)
- Optimize heart failure management preoperatively with cautious use of diuretics 1
- Continue beta-blockers if patient is already on them, but avoid new initiation immediately before surgery
Hemodynamic Goals During AVR
Maintain key hemodynamic parameters:
- Heart rate: 60-70 bpm (avoid tachycardia which reduces diastolic filling time)
- Mean arterial pressure: 65-90 mmHg (maintain coronary perfusion)
- Preload: Maintain adequate filling pressures
- Contractility: Preserve inotropic state
- Sinus rhythm: Critical for maintaining cardiac output
Avoid:
- Tachycardia (reduces diastolic filling time)
- Bradycardia (reduces cardiac output)
- Hypotension (compromises coronary perfusion)
- Hypovolemia (reduces preload)
- Vasodilation (reduces afterload and can cause hypotension)
Monitoring Requirements
- Standard ASA monitors plus:
- Invasive arterial blood pressure monitoring
- Central venous pressure monitoring
- Pulmonary artery catheter or minimally invasive cardiac output monitoring 3
- Transesophageal echocardiography (TEE) for real-time assessment of ventricular function, volume status, and valvular function
Anaesthetic Technique
Induction
- Etomidate (0.2-0.3 mg/kg) is preferred for induction due to minimal hemodynamic effects
- Alternative: Remimazolam has shown promise in preserving cardiac output in patients with severe AS 4
- Opioids (fentanyl 5-10 μg/kg or equivalent) to blunt sympathetic response
- Avoid propofol as a sole induction agent due to vasodilatory effects
- Muscle relaxants with minimal cardiovascular effects (rocuronium, cisatracurium)
- Have vasopressors readily available (phenylephrine, norepinephrine)
Maintenance
- Balanced technique with:
- Volatile agents at low to moderate concentrations (0.5-0.8 MAC) or total intravenous anesthesia
- High-dose opioids to maintain hemodynamic stability
- Consider remifentanil infusion for its titratable effects and rapid offset
Fluid Management
- Goal-directed fluid therapy guided by dynamic parameters (stroke volume variation, TEE)
- Maintain euvolemia - avoid both hypovolemia and hypervolemia
- Use crystalloids judiciously; consider albumin or balanced solutions
Management of Hemodynamic Instability
Hypotension
- First-line: Phenylephrine (pure α-agonist) to maintain vascular tone
- Second-line: Norepinephrine for combined α and mild β effects
- Avoid pure vasodilators (nitroglycerin, nitroprusside)
- Volume administration if hypovolemia is confirmed by TEE or other monitoring
Low Cardiac Output
- First-line: Optimize preload and heart rate
- Second-line: Inotropic support with epinephrine or dobutamine
- Consider milrinone only if adequate preload is ensured (due to vasodilatory effects)
Arrhythmias
- Maintain electrolyte balance (particularly potassium and magnesium)
- Treat atrial fibrillation promptly with electrical cardioversion if hemodynamically unstable
- Amiodarone for pharmacological rhythm control if needed
Cardiopulmonary Bypass (CPB) Considerations
- Ensure adequate anticoagulation before CPB initiation
- Careful attention to de-airing procedures to prevent air embolism
- Gradual weaning from CPB with inotropic support as needed
- TEE assessment of new valve function and ventricular performance
Post-Bypass Management
- Optimize preload to maintain adequate cardiac output
- Inotropic support if needed (dobutamine, epinephrine)
- Vasopressors to maintain systemic vascular resistance
- Maintain sinus rhythm - treat arrhythmias promptly
- Assess for paravalvular leaks or other valve-related complications
Common Pitfalls and Caveats
- Avoid rapid changes in hemodynamics - titrate all medications slowly
- Beware of vasodilation from anesthetic agents, especially in induction phase
- Recognize that AS patients have fixed cardiac output - they cannot increase stroke volume to compensate for decreased SVR
- Maintain sinus rhythm - loss of atrial kick can cause significant hemodynamic deterioration
- Prevent tachycardia at all costs - it reduces diastolic filling time and coronary perfusion
- Monitor for post-CPB right ventricular dysfunction which can occur after prolonged CPB
Post-Operative Care
- Continue invasive monitoring in ICU
- Gradual weaning of inotropic and vasopressor support
- Early detection and management of arrhythmias
- Optimize analgesia to prevent sympathetic stimulation
- Monitor for bleeding complications and manage coagulopathy
By adhering to these principles of maintaining hemodynamic stability, careful monitoring, and appropriate pharmacological interventions, patients with severe aortic stenosis can safely undergo aortic valve replacement with minimal perioperative morbidity and mortality.