Question

A patient with pheochromocytoma is undergoing surgery and has not been administered with alpha receptor blocker. If he is administered with intravenous propranolol, then which of the following effects will be evident?

• A. There will be a rise in the blood pressure
• B. There will be a fall in the blood pressure
• C. The blood pressure will remain unchanged
• D. The patient may suffer severe bronchoconstriction

Answer 1

The Correct Option is A

Pheochromocytoma is a condition characterized by a tumor in the adrenal glands that leads to excessive production of catecholamines, mainly adrenaline and noradrenaline. These hormones primarily act on both alpha and beta-adrenergic receptors, leading to increased heart rate and blood pressure.

In the given scenario, the patient with pheochromocytoma is undergoing surgery. The proposed intervention is the administration of propranolol, a non-selective beta-blocker, without prior administration of an alpha blocker.

1. Mechanism of Action:
   • Propranolol blocks beta-adrenergic receptors (beta-1 and beta-2), which would normally decrease heart rate and force of contraction, as well as dilate blood vessels and bronchi.
   • Without the blockade of alpha receptors, catecholamines continue to bind predominantly to alpha receptors, which causes vasoconstriction.
2. Consequences of Propranolol Administration:
   • By blocking beta-2 receptors, propranolol inhibits the vasodilatory effects that otherwise oppose alpha-mediated vasoconstriction.
   • This leads to unopposed alpha adrenergic activity which results in an increase in blood pressure due to vasoconstriction.
3. Analysis of Options:
   • There will be a rise in the blood pressure: This is correct because the alpha receptor stimulation remains unopposed, potentiating vasoconstriction.
   • There will be a fall in the blood pressure: Incorrect, as the vasodilatory effects cancelled by beta-blockade will not counteract alpha-induced vasoconstriction.
   • The blood pressure will remain unchanged: Incorrect, because the existing sympathetic activity affects blood dynamics.
   • The patient may suffer severe bronchoconstriction: While bronchoconstriction can occur due to beta-2 blockade, it is not the primary concern in this scenario regarding blood pressure dynamics.

Conclusion: Administering propranolol in this context leads to a rise in blood pressure because the beta receptor blockade results in unopposed alpha-mediated vasoconstriction.