## Mechanism of Propofol-Induced Hypotension **Key Point:** Propofol causes dose-dependent hypotension through two primary mechanisms: direct myocardial depression (negative inotropic effect) and peripheral vasodilation via inhibition of sympathetic tone. ### Clinical Features Supporting This Diagnosis | Feature | Finding | Significance | |---------|---------|---------------| | **Timing** | Within 2 minutes of induction | Consistent with propofol's rapid onset | | **SpO₂** | 98% on 100% O₂ | Rules out hypoxia as primary cause | | **Breath sounds** | Bilateral and easy | Rules out airway obstruction or aspiration | | **Heart rate** | 68 bpm (normal) | No compensatory tachycardia; not hypovolemia | | **Bilateral breath sounds** | Present | Rules out tension pneumothorax | ### Why This Patient Is at Risk 1. **Elderly age** — reduced cardiovascular reserve 2. **Comorbidities** — hypertension and diabetes impair autoregulation 3. **Propofol dose** — 2 mg/kg is standard but can cause 20–30% reduction in MAP in susceptible patients **High-Yield:** Propofol hypotension is dose-dependent and reversible. The lack of hypoxia, normal heart rate, and easy ventilation exclude airway compromise, anaphylaxis, and acute cardiac ischemia. ### Management 1. **Reduce propofol dose** in future inductions (consider 1.5 mg/kg in elderly/comorbid patients) 2. **Fluid bolus** — 500 mL crystalloid IV 3. **Vasopressor** — phenylephrine 50–100 mcg IV or noradrenaline infusion if persistent 4. **Avoid further CNS depressants** until BP recovers **Clinical Pearl:** Succinylcholine itself does not cause hypotension; it may cause transient hyperkalemia and bradycardia (via muscarinic effects) but not the immediate, sustained hypotension seen here. The temporal relationship to propofol administration is diagnostic. [cite:Stoelting's Pharmacology and Physiology in Anesthetic Practice Ch 4]
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