A 72-year-old woman with severe aortic stenosis (valve area 0.6 cm²) and chronic kidney disease (eGFR 28 mL/min) is undergoing emergency repair of a perforated peptic ulcer. After induction with etomidate 0.2 mg/kg IV and vecuronium 0.1 mg/kg IV, blood pressure drops from 140/90 mmHg to 78/48 mmHg within 3 minutes. SpO₂ remains 98% on 100% O₂, heart rate is 52 bpm, and CVP is elevated at 8 cm H₂O. The surgeon reports minimal blood loss. What is the primary mechanism of hypotension in this case?

Explanation

## Pathophysiology of Hypotension in Aortic Stenosis ### Clinical Context This patient has **critical aortic stenosis** with severe afterload dependence. In aortic stenosis, the left ventricle relies on: - **High preload** (to stretch the ventricle and increase contractility via Frank-Starling mechanism) - **High afterload** (to maintain coronary perfusion pressure across the stenotic valve) - **Maintained heart rate** (to preserve cardiac output in fixed-stroke-volume physiology) **High-Yield:** Anesthetic induction causes catastrophic hemodynamic collapse in aortic stenosis because: 1. **Propofol/Etomidate** → myocardial depression + vasodilation 2. **Loss of sympathetic tone** → reduced systemic vascular resistance (SVR) 3. **Reduced preload** → decreased left ventricular filling 4. **Result:** Cardiac output = (Preload − Afterload) / Contractility drops precipitously ### Why Other Options Are Wrong | Finding | Hypovolemia | Anesthetic Depression | Sepsis | ACS | |---------|-------------|----------------------|--------|-----| | **CVP** | Low (< 2 cm H₂O) | Normal or high | Variable | Normal | | **Minimal blood loss** | Rules out | — | — | — | | **Heart rate** | Tachycardia (> 100) | Bradycardia (52) ✓ | Tachycardia | Variable | | **Timing** | Gradual | **Immediate (3 min)** ✓ | Hours | Minutes–hours | | **SpO₂ on 100% O₂** | Normal | Normal ✓ | May be low | Normal | | **Elevated CVP** | Excludes | Consistent ✓ | Possible | Possible | **Key Point:** The **elevated CVP (8 cm H₂O)** is the critical clue—it rules out hypovolemia and points to **impaired cardiac output despite adequate filling pressure**. This is the hallmark of anesthetic-induced depression in a patient with fixed stroke volume. ### Mechanism in Aortic Stenosis ```mermaid flowchart TD A[Induction: Etomidate + Vecuronium]:::action --> B[Myocardial Depression]:::outcome A --> C[Sympathetic Blockade]:::outcome B --> D[↓ Contractility]:::urgent C --> E[↓ SVR & Preload]:::urgent D --> F[↓ Stroke Volume]:::urgent E --> F F --> G[↓ Cardiac Output]:::urgent G --> H[Hypotension]:::urgent G --> I[↓ Coronary Perfusion]:::urgent I --> J[Myocardial Ischemia Risk]:::urgent ``` ### Clinical Pearl **Aortic stenosis is a relative contraindication to propofol.** Etomidate was correctly chosen here (preserves SVR better), but even etomidate causes myocardial depression. The **bradycardia (52 bpm)** is a red flag—in aortic stenosis, bradycardia is catastrophic because CO = HR × SV, and SV is already fixed by the stenotic valve. ### Management 1. **Immediate:** Reduce anesthetic depth; consider vasopressor (phenylephrine 50–100 μg IV bolus) 2. **Fluid:** Cautious bolus (250 mL) to restore preload 3. **Avoid:** Volatile anesthetics (myocardial depression); use opioid-based anesthesia 4. **Maintain:** Heart rate 60–80 bpm; avoid bradycardia 5. **Monitor:** Invasive BP, ECG for ischemia, consider TEE if available **Warning:** Do NOT use vasodilators (nitroglycerin, nitroprusside) in aortic stenosis—they reduce coronary perfusion pressure and worsen ischemia. [cite:Miller's Anesthesia 8e Ch 20; Stoelting's Pharmacology and Physiology in Anesthetic Practice 5e Ch 3]