A 68-year-old male with a history of hypertension and diabetes mellitus is undergoing emergency laparotomy for perforated peptic ulcer. Induction is planned with propofol. Intraoperatively, after intubation and initiation of mechanical ventilation with FiO₂ 0.5, his blood pressure drops from 130/80 mmHg to 85/50 mmHg within 2 minutes of propofol administration. Heart rate increases from 78 to 110 bpm. SpO₂ remains 98%. Which of the following mechanisms BEST explains the hemodynamic collapse in this patient?

Explanation

## Propofol-Induced Hemodynamic Collapse: Mechanism **Correct Answer: Direct myocardial depression and peripheral vasodilation with preserved baroreceptor reflex arc** Propofol causes hemodynamic collapse through a **dual mechanism**: ### Mechanism of Action: 1. **Direct myocardial depression** — reduces cardiac contractility via inhibition of intracellular calcium mobilization and reduced sensitivity of myofilaments to calcium 2. **Peripheral vasodilation** — mediated by: - Direct smooth muscle relaxation - Inhibition of sympathetic outflow from the CNS - Reduced norepinephrine release from nerve terminals ### Why the Baroreceptor Reflex is Preserved: - The baroreceptor reflex arc remains intact - However, it is **overwhelmed** by the magnitude of vasodilation and myocardial depression - The reflex attempts compensation → **tachycardia (HR 78→110 bpm)** — this is the preserved reflex response - But the tachycardia is **insufficient** to maintain cardiac output, hence hypotension persists ### Clinical Pearl: **Propofol causes dose-dependent cardiovascular depression.** In elderly patients, those with hypovolemia, or critical illness, this effect is exaggerated. The preserved tachycardia (not bradycardia) is a key distinguishing feature. ### High-Yield Point: The combination of **hypotension + tachycardia** after propofol induction is pathognomonic for propofol's dual effect on the heart and vasculature, NOT unopposed parasympathomimesis or sympatholysis without reflex compensation.