Current concepts: pheochromocytoma: diagnosis, localization and management

On the basis of this experience, we propose that normal clonidine suppression should consist of a fall in the basal values of norepinephrine and epinephrine to a level below 500 pg per milliliter two or three hours after the administration of 0.3 mg of clonidine. All cases of severe hypotension requiring treatment have occurred in patients who were receiving antihypertensive medications or had other conditions that would tend to augment the effect of any antihypertensive agent.18, 19 In particular, marked volume depletion should be avoided, and any β-adrenergic blocking agent should be discontinued about 48 hours before performance of the test. Since clonidine has a potent vagotonic effect, concomitant β-adrenergic blockade could lead to marked bradycardia, with further decreases in stroke volume and cardiac output resulting in severe hypotension. A small percentage of patients may have moderate elevations in plasma catecholamine levels (less than 1000 pg per milliliter, or 5.91 nmol per liter). [...]whenever the clinical presentation is suggestive of pheochromocytoma and plasma catecholamine levels are only moderately increased, further evaluation should be performed. [...]failure of the blood pressure to fall abruptly when the tumor is removed, which is often a signal that another tumor is present, cannot be appreciated. [...]α-adrenergic blockade may impede the surgeon's ability to locate small extraadrenal tumors, because blood pressure will not rise when the tumor is palpated during exploration.