Treatment for pheochromocytomas

[MudPhud20XX]

Kaplan says start w/ alpha blocker such as phenoxybenzamine first and then use beta blocker. Why not the other way?

Many thanks in advance.

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[surgok]

In pheo, afterload is already high. If you use BB to reduce contractility of the heart, this may lead to low output cardiovascular collapse.
That's why you use alpha blockers to loosen up those blood vessels, then use BB to counteract reflex tachycardia.

 

[thehundredthone]

Actually, more importantly, if you start with a beta blocker, the unopposed alpha agonism upon catecholamine release can cause severe hypertension. The catecholamine release in pheochromocytoma is episodic, so afterload is not consistently high. Beta blockers are used more for their negative chronotropic effect to control tachyarrhythmias.

 

[surgok]

Actually, more importantly, if you start with a beta blocker, the unopposed alpha agonism upon catecholamine release can cause severe hypertension. The catecholamine release in pheochromocytoma is episodic, so afterload is not consistently high. Beta blockers are used more for their negative chronotropic effect to control tachyarrhythmias.

You are right. Don't know why I was thinking that way.

 

[dyspareunia]

Also, isn't phenoxybenzamine used as prophylaxis before surgery to remove it?

 

[bulldogmed]

Also, isn't phenoxybenzamine used as prophylaxis before surgery to remove it?

yes. It's an irreversible inhibitor, so it's effects will last 2-3 days I think.

 

[thehundredthone]

Also, isn't phenoxybenzamine used as prophylaxis before surgery to remove it?

And phentolamine during the surgery itself.

 

[notbobtrustme]

Actually, more importantly, if you start with a beta blocker, the unopposed alpha agonism upon catecholamine release can cause severe hypertension. The catecholamine release in pheochromocytoma is episodic, so afterload is not consistently high. Beta blockers are used more for their negative chronotropic effect to control tachyarrhythmias.

same with cocaine overdose, never treat with a beta-blocker because you'll have unopposed alpha vasoconstriction and clamp down on all the vessels.