A 68-year-old woman with severe aortic stenosis (valve area 0.8 cm²) and ejection fraction 35% is scheduled for transurethral resection of bladder tumor under regional anesthesia. The anesthesiologist is considering spinal anesthesia with 10 mg hyperbaric bupivacaine. Baseline blood pressure is 145/88 mmHg, heart rate 72/min, and CVP 8 mmHg. What is the primary concern with spinal anesthesia in this patient?

Explanation

## Pathophysiology of Spinal Anesthesia in Aortic Stenosis ### Hemodynamic Effects of Spinal Anesthesia Spinal anesthesia causes: 1. **Sympathetic blockade** → vasodilation and reduced preload 2. **Reduced systemic vascular resistance (SVR)** 3. **Decreased cardiac output** (CO = SVR × BP) ### Why Aortic Stenosis Is Uniquely Vulnerable | Physiologic Factor | Normal Patient | Aortic Stenosis Patient | |-------------------|----------------|------------------------| | Cardiac output dependency | Moderate | **Critical** — fixed stroke volume due to stenotic valve | | Preload sensitivity | Moderate | **Extreme** — Frank-Starling curve operates on steep portion | | Afterload dependency | Moderate | **Extreme** — maintains CO via increased afterload | | Coronary perfusion | Adequate | **Marginal** — LV hypertrophy + reduced diastolic time | | Compensation for hypotension | ↑ HR, ↑ contractility | **Limited** — cannot increase CO adequately | **Key Point:** In aortic stenosis, the left ventricle is **afterload-dependent**. The stenotic valve acts as a fixed resistance; to maintain adequate cardiac output, the ventricle relies on high systemic vascular resistance and ventricular hypertrophy. Spinal anesthesia's sympathetic blockade causes sudden loss of this critical afterload support, resulting in **catastrophic hypotension**. **High-Yield:** The combination of: - Fixed stroke volume (stenotic valve) - Loss of preload (venous pooling from sympathetic blockade) - Loss of afterload (SVR reduction) - Marginal coronary perfusion (LV hypertrophy + diastolic dysfunction) ...creates a **perfect storm** for severe hypotension, myocardial ischemia, and cardiogenic shock. ### Clinical Pearl **Spinal anesthesia is relatively contraindicated in severe aortic stenosis.** If regional anesthesia is chosen, epidural (which allows slower sympathetic blockade and titration) is safer than spinal. Alternatively, general anesthesia with careful hemodynamic management is preferred. ### Management Strategy 1. **Avoid spinal anesthesia** in symptomatic or severe AS (valve area <1.0 cm²) 2. If regional anesthesia essential: - Prefer **epidural** over spinal (slower onset, titratable) - Maintain aggressive fluid resuscitation and vasopressor support (phenylephrine preferred — pure α-agonist maintains afterload) - Have vasopressors drawn up and ready - Avoid rapid sympathetic blockade 3. **General anesthesia** with etomidate or low-dose propofol + opioids is often safer 4. Maintain sinus rhythm and avoid tachycardia (reduces diastolic filling time) [cite:Barash Clinical Anesthesia 8e Ch 30; Morgan Textbook of Clinical Anesthesiology 6e Ch 28]