A 58-year-old man with hypertension (on amlodipine) and type 2 diabetes presents for elective laparoscopic cholecystectomy. After induction with propofol 2 mg/kg and intubation with succinylcholine, his blood pressure drops from 140/90 mmHg to 85/50 mmHg within 2 minutes. Oxygen saturation remains 98% on 100% FiO₂. Heart rate is 78 bpm. There is no anaphylaxis, no malignant hyperthermia signs, and no obvious surgical bleeding. What is the most likely cause of hypotension?

Explanation

## Mechanism of Propofol-Induced Hypotension **Key Point:** Propofol causes profound hypotension through two mechanisms: direct myocardial depression (decreased contractility) and peripheral vasodilation (decreased systemic vascular resistance). This is the most common cause of induction-related hypotension in elective surgery. ### Why Propofol Causes Hypotension 1. **Direct myocardial depression** — reduces cardiac output by 20–30% 2. **Peripheral vasodilation** — decreases SVR via GABA-A receptor activation and inhibition of sympathetic outflow 3. **Blunted baroreceptor reflex** — impairs compensatory tachycardia **Clinical Pearl:** Propofol-induced hypotension is dose-dependent and more pronounced in elderly, hypovolemic, or critically ill patients. This patient received standard induction dosing (2 mg/kg) and has no signs of anaphylaxis (no rash, bronchospasm, or angioedema) or malignant hyperthermia (no muscle rigidity, hyperthermia, or rhabdomyolysis). ### Timeline & Exclusion of Alternatives | Finding | Propofol Hypotension | Hyperkalemia (Succinylcholine) | Anaphylaxis | ACS | |---------|----------------------|--------------------------------|-------------|-----| | **Onset** | Immediate (< 2 min) | 30 sec–1 min | 30 sec–5 min | Minutes–hours | | **SpO₂** | Normal initially | Normal | ↓ (bronchospasm) | Normal initially | | **HR** | Often ↓ or unchanged | ↑↑ (peaked T waves, VF risk) | ↑↑ | Variable | | **Anaphylaxis signs** | None | None | Rash, stridor, angioedema | None | | **MH signs** | None | None | None | None | **High-Yield:** In this case, SpO₂ is maintained at 98%, heart rate is normal (78 bpm), and there are no signs of anaphylaxis or hyperkalemia-induced dysrhythmia. The hypotension is isolated and follows propofol induction — classic presentation. ### Management 1. **Reduce FiO₂ to 30–40%** (if SpO₂ allows) to prevent absorption atelectasis 2. **Fluid bolus** — 500 mL crystalloid IV 3. **Vasopressor** — phenylephrine 50–100 mcg IV or noradrenaline infusion if persistent 4. **Reduce propofol dose** in future inductions (consider etomidate or ketamine in high-risk patients) **Mnemonic: PROPOFOL Hypotension — PRO-Profound Reduction Of Perfusion pressure by Opioid-Free Outflow Loss** [cite:Miller's Anesthesia 8e Ch 9]