How to manage patients with aortic stenosis undergoing surgery with spinal (regional) anesthesia to avoid hypotension?

Management of Aortic Stenosis with Spinal Anesthesia

Elevated-risk surgery with spinal anesthesia is reasonable in patients with asymptomatic severe aortic stenosis when combined with appropriate intraoperative and postoperative hemodynamic monitoring, careful titration of local anesthetic dose, and immediate availability of vasopressor support. 1

Key Hemodynamic Principles

The fundamental challenge in aortic stenosis patients is maintaining adequate cardiac output through a fixed obstruction. These patients are critically dependent on:

• Preload maintenance - The hypertrophied, non-compliant left ventricle requires adequate filling pressures 1
• Sinus rhythm - Loss of atrial kick can reduce cardiac output by 25-40% 1
• Avoidance of tachycardia - Shortened diastolic filling time reduces coronary perfusion and stroke volume 1
• Prevention of hypotension - Decreased coronary perfusion pressure leads to myocardial ischemia, arrhythmias, and cardiac failure 1

Spinal Anesthesia Technique Modifications

Dose and Volume Reduction

Use low-dose, low-volume unilateral spinal techniques to minimize sympathetic blockade and preserve hemodynamic stability. 2, 3

• Administer 5 mg bupivacaine in 1.5 mL volume for lower extremity procedures 3
• Consider combined spinal-epidural (CSE) technique allowing incremental dosing and titration 2
• Perform slow, controlled injection to limit cephalad spread 3
• Maintain lateral positioning during and after injection to achieve unilateral block 3

Monitoring Requirements

Implement continuous arterial pressure monitoring before induction, as intermittent monitoring detects only 50% of hypotensive episodes compared to continuous monitoring. 1

• Insert arterial catheter before spinal placement, not after 1
• Consider pulmonary artery catheter or advanced hemodynamic monitoring for severe stenosis (valve area <0.6 cm²) 1
• Monitor continuously for arrhythmias, particularly atrial fibrillation 1

Hypotension Prevention and Management

Preemptive Measures

Aggressively preload before spinal placement, but avoid excessive fluid administration in patients with small left ventricular chambers or diastolic dysfunction. 1

• Administer 250-500 mL crystalloid before spinal injection 2, 3
• Use passive leg raise (PLR) test to assess fluid responsiveness (88% sensitivity, 92% specificity) 4
• Avoid fluid boluses if PLR test is negative 4

Vasopressor Strategy

Phenylephrine is the preferred first-line vasopressor for hypotension in aortic stenosis patients undergoing spinal anesthesia. 5, 4

• Prepare phenylephrine 100 mcg/mL solution before spinal placement 5
• Initial bolus: 50-100 mcg IV for hypotension (MAP <65 mmHg or SBP <90 mmHg) 1, 5
• Infusion dosing: 0.5-1.4 mcg/kg/min, titrated to maintain MAP ≥65 mmHg 5
• Phenylephrine produces reflex bradycardia, which is beneficial in aortic stenosis by prolonging diastolic filling time 4, 5

Target Blood Pressure

Maintain mean arterial pressure ≥65 mmHg, with higher targets (MAP 70-80 mmHg) for patients with baseline hypertension or coronary disease. 1

• Intraoperative MAP <60 mmHg is associated with myocardial injury, acute kidney injury, and death 1
• In severe aortic stenosis, even brief hypotension can precipitate myocardial ischemia and cardiac failure 1
• Treat hypotension within 1-2 minutes of onset, not after 5-10 minutes 1

Risk Stratification

Higher Risk Features Requiring Enhanced Monitoring

• Symptomatic severe aortic stenosis (OR 2.7 for perioperative complications) 1
• Valve area <0.6 cm² or mean gradient >50 mmHg 1, 6
• Coexisting moderate-severe mitral regurgitation (OR 9.8 for complications) 1
• Pre-existing coronary artery disease (OR 2.7 for complications) 1
• Left ventricular ejection fraction <50% 1

Acceptable Risk Profile

Asymptomatic patients with severe aortic stenosis have 30-day mortality of 2.1% and MI rate of 3.0% with appropriate monitoring, compared to historical rates of 13% mortality. 1, 6

Critical Pitfalls to Avoid

1. Never use high-dose, bilateral spinal techniques - Standard spinal doses cause profound sympathectomy and refractory hypotension 2, 3

2. Never delay vasopressor administration - Waiting for "adequate fluid resuscitation" before vasopressors worsens outcomes; treat hypotension based on etiology 4

3. Avoid beta-blockers for rate control unless patient has reduced ejection fraction, prior MI, or life-threatening arrhythmias 1, 7

4. Do not use ephedrine as first-line vasopressor - Tachycardia from ephedrine is poorly tolerated in aortic stenosis 4

5. Never assume postoperative stability - Postoperative hypotension is often unrecognized, prolonged, and potentially more harmful than intraoperative hypotension 1

Postoperative Management

Monitor blood pressure every 15 minutes for the first 2-4 hours postoperatively, with continuous monitoring if any instability occurs. 1, 4

• Postoperative hypotension (SBP <90-100 mmHg or MAP <60-65 mmHg) is associated with acute kidney injury, cardiovascular events, and mortality 1
• Maintain vasopressor infusion until sympathetic blockade fully resolves (typically 2-4 hours) 4
• Consider ICU admission for severe stenosis (valve area <0.6 cm²) or any intraoperative instability 1