A patient with pheochromocytoma requires surgical resection. During anesthetic induction, the patient develops hypertensive crisis. The resident proposes immediate IV labetalol. The attending surgeon objects. What is the pharmacological basis for this objection?
- A Labetalol causes paradoxical hypertension by allowing unopposed alpha stimulation when beta receptors are blocked first
- B In pheochromocytoma, alpha blockade must be established before beta blockade to prevent unopposed alpha-mediated vasoconstriction ✓
- C Labetalol's beta-1 blockade reduces cardiac output, worsening the hypertension by triggering reflex tachycardia
- D Labetalol has insufficient duration of action for intraoperative blood pressure management
Explanation
In pheochromocytoma, catecholamines act on both alpha and beta receptors. If a non-selective beta blocker is given first, the vasodilatory beta-2 effect is removed, leaving unopposed alpha-mediated vasoconstriction and potentially catastrophic hypertension. While labetalol blocks both, the ratio of beta:alpha blockade is 7:1 IV, meaning alpha blockade may be insufficient relative to beta blockade. The established protocol is to give alpha blockers (phenoxybenzamine) for at least 10-14 days preoperatively before introducing any beta blocker. Labetalol alone is suboptimal compared to a sequential approach.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
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Written and medically reviewed by the StethoPrep medical team.