Pheochromocytoma Flashcards
What is a pheochromocytoma?
A catecholamine-secreting tumor of chromaffin tissue.
Where are pheochromocytomas located?
They are usually in the adrenal medullae or sympathetic paraganglia. 90% are found in the adrenal medulla.
What is the prevalence of pheochromocytomas?
1 in 1,000 to 5 in 100,000
What substances does the adrenal medulla secrete?
The adrenal medulla primarily secretes three substances, all of which are catecholamines. The catecholamines are epinephrine, norepinephrine, and dopamine.
What does the adrenal cortex secrete?
The adrenal cortex secretes more than 30 different corticosteroids. These can be divided into two major classes, the mineralocorticoids and the glucocorticoids.
What are some clinical features associated with a pheochromocytoma?
The classic triad is severe headache, diaphoresis, and palpatations.
How do you diagnose a pheochromocytoma?
The biochemical diagnosis is based on the fact that pheochromocytomas release an excessive amount of cathecholamines and metabolites. 24-hour total metanephrines (epinephrine, norepinephrine, dopamine, and vanillylmandelic acid (VMA))
How do you pharmacologically prepare the patient with a pheochromocytoma for surgery?
The major goal is to partially block the responses to catecholamines and to avoid the pressor effects of cathecholamines.
What is the cornerstone of pre-operative management of the patient with a pheochromocytoma?
Administration of alpha-adrenergic blockers. The most commonly used agents have been phenoxybenzamine (POB), prazosin, and phentolamine as a constant infusion.
Historically, what is the most commonly used pharmacologic agent for alpha-adrenergic blockade in a patient with a pheochromocytoma?
Phenoxybenzamine because of its relatively long duration of action and ease of administration. It irreversibly alkylates alpha-1 adrenergic receptors on vascular smooth muscle, thereby making them non-functional
What are some of the side effects of alpha-adrenergic blockade?
Postural hypotension and reflex tachycardia.
How do you treat the side effects of alpha-adrenergic blockade?
Administration of fluid and administration of beta-blockade.
When should you start beta-adrenergic blockers (beta-blockers)?
Many feel that beta-adrenergic blockers should only be used when tachycardia or arrhythmias exist. If using beta-blockers, do not start until after alpha-adrenergic blockers have been started.
What other aspects of pre-operative management are important in patients with a pheochromocytoma?
The circulating blood volume is decreased in many patients with pheochromocytomas. Therefore, many physicians support the idea of fluid administration before surgery, while patients receive alpha-adrenergic blockade.
What drugs should be avoided during surgery for a pheochromocytoma?
Droperidol (haloperidol), morphine, atracurium, pancuronium, ketamine, ephedrine, halothane, cocaine metoclopramide, curare.
