A 60-year-old man taking a non-selective beta-blocker for hypertension is given a subcutaneous dose of adrenaline for anaphylaxis. Which of the following haemodynamic consequences is most likely?
- A Paradoxical hypertension with reflex bradycardia due to unopposed alpha stimulation ✓
- B Marked bradycardia with a rise in diastolic blood pressure
- C Tachycardia with a fall in both systolic and diastolic blood pressure
- D No change in blood pressure because adrenaline effects are fully blocked
Correct answer: A. Paradoxical hypertension with reflex bradycardia due to unopposed alpha stimulation
Explanation
When beta receptors are blocked, the beta-2-mediated vasodilation in skeletal muscle is prevented; adrenaline's alpha-1 vasoconstrictor effect is then unopposed, causing a sharp rise in blood pressure. This hypertension triggers a baroreceptor-mediated reflex bradycardia. This 'epinephrine reversal' scenario is a classic hazard of using adrenaline in patients on non-selective beta-blockers.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
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