A 58-year-old man with a history of hypertension and type 2 diabetes mellitus presents for elective laparoscopic cholecystectomy. His baseline blood pressure is 145/92 mmHg and heart rate is 88 bpm. During pre-operative assessment, you note he is on metoprolol and amlodipine. After pre-oxygenation and standard monitoring, induction is initiated. Within 30 seconds of IV administration of the induction agent, his blood pressure drops to 95/58 mmHg and heart rate increases to 105 bpm. The patient remains unconscious and airway is secured without difficulty. Which induction agent was most likely used?

Explanation

## Analysis of Hemodynamic Changes Post-Induction ### Clinical Presentation The patient experienced significant hypotension (145/92 → 95/58 mmHg) with compensatory tachycardia (88 → 105 bpm) within 30 seconds of IV induction agent administration, despite being on antihypertensive therapy. The rapid onset and magnitude of blood pressure drop are key diagnostic clues. ### Comparative Hemodynamic Effects of IV Induction Agents | Agent | Mechanism of BP Drop | Degree of Hypotension | Heart Rate Response | Clinical Pearl | |-------|---------------------|----------------------|-------------------|----------------| | **Propofol** | Peripheral vasodilation + myocardial depression + reduced sympathetic tone | **Marked (20–40% drop)** | Reflex tachycardia common | Most hypotensive agent; dose-dependent | | Etomidate | Minimal vasodilation; preserved sympathetic reflexes | Minimal to none | Stable or slight ↑ | Hemodynamically most stable | | Ketamine | Sympathomimetic (↑ catecholamine release) | Minimal or ↑ BP | Tachycardia from sympathetic stimulation | Maintains or increases BP | | Thiopentone | Myocardial depression + vasodilation | Moderate (10–20% drop) | Variable | Less hypotensive than propofol | ### Why Propofol? **Key Point:** Propofol causes the most profound and rapid hypotension among IV induction agents due to: 1. Direct myocardial depression (negative inotropic effect) 2. Peripheral vasodilation via GABA~A~ receptor activation 3. Reduced sympathetic outflow 4. Blunted baroreceptor reflex (relative to other agents) The 50 mmHg systolic drop in this hypertensive patient is characteristic of propofol's dose-dependent hemodynamic effects. ### Clinical Pearl **High-Yield:** In elderly, hypovolemic, or cardiovascularly compromised patients, propofol dosing should be reduced by 25–50% to minimize hypotension. This patient's antihypertensive medications likely potentiated propofol's vasodilatory effects. ### Why Not the Others? - **Etomidate:** Would maintain BP near baseline; tachycardia alone would be unusual without hypotension. - **Ketamine:** Would maintain or increase BP via sympathomimetic effects; hypotension would be unexpected. - **Thiopentone:** Causes moderate hypotension but typically less severe than propofol; less commonly used in modern practice. ## Management Implications 1. Fluid bolus (crystalloid 250–500 mL IV) 2. Vasopressor support (phenylephrine 50–100 μg IV or noradrenaline infusion) 3. Reduce propofol dose in future inductions for this patient 4. Consider etomidate or ketamine for induction in hemodynamically unstable patients