A 52-year-old man with hypertension (on amlodipine) undergoes elective total knee replacement under spinal anesthesia. The procedure lasts 90 minutes. Intraoperatively, his blood pressure drops from 140/90 mmHg to 85/50 mmHg at 45 minutes, and he develops bradycardia (HR 42/min). He is conscious and alert. The anesthesiologist administers oxygen, increases IV fluids, and gives 6 mg ephedrine IV. Despite these measures, his blood pressure remains 90/55 mmHg and heart rate is 48/min. What is the most likely diagnosis?

Explanation

## Clinical Presentation Analysis **Key Point:** The constellation of hypotension + bradycardia (paradoxical response) in the setting of spinal anesthesia, unresponsive to standard vasopressor and fluid therapy, is pathognomonic for the Bezold-Jarisch reflex. ## Mechanism of Bezold-Jarisch Reflex The Bezold-Jarisch reflex (also called the **vasovagal response** in spinal anesthesia context) occurs when: 1. Spinal anesthesia causes sympathetic blockade → peripheral vasodilation and venous pooling 2. Decreased venous return → reduced left ventricular preload 3. Paradoxically, this triggers **mechanoreceptors in the left ventricular wall** (C-fibers) that sense "empty chamber" 4. Reflex vagal discharge → profound bradycardia + further vasodilatation (not vasoconstriction) 5. Result: **hypotension + bradycardia** — a dangerous combination ## Why Standard Therapy Failed | Intervention | Why It Failed | |---|---| | IV fluids | Venous pooling prevents adequate preload restoration | | Ephedrine (sympathomimetic) | Reflex is **vagal-mediated**; sympathomimetics may paradoxically worsen bradycardia via baroreceptor feedback | | Oxygen | Does not address the underlying hemodynamic collapse | ## Correct Management **High-Yield:** The definitive treatment is **atropine (0.5–1 mg IV)** to block vagal tone, combined with: - Aggressive IV fluid resuscitation (crystalloid bolus) - Vasopressors (phenylephrine preferred over ephedrine in this context) - Trendelenburg positioning - Supplemental oxygen ## Clinical Pearl The **paradoxical bradycardia** in the face of hypotension is the key discriminator. In hypovolemic shock or sepsis, tachycardia is the expected compensatory response. Here, the heart rate is inappropriately low — a red flag for vagal hyperactivity. ## Mnemonic **BJ-REFLEX** = **B**ezold-**J**arisch = **R**eflex **E**jection **F**raction **L**ow **E**mpty **X** (paradoxical bradycardia) [cite:Gupta & Sharma Regional Anesthesia Ch 8]