Pheochromocytoma: Why Alpha and Beta Blockers?

Pheochromocytoma= A rare catecholamine producing tumour that originate from chromaffin cells in the adrenal medulla. Patients classically present with: paroxysmal hypertension, palpitations, headache, and diaphoresis. The frequency varies from daily, weekly or monthly.  Patients generally have orthostatic hypotension on physical exam.

NOTE: Surgery is the definitive treatment. Pre-operatively the patient must be given both alpha- AND beta-blocking agents!

• Alpha-blocker= opposes catecholamine-induced vasoconstriction
• Beta-blocker= opposes the subsequent reflex tachycardia secondary to alpha-blockade

WARNING: Never give a patient with a pheochromocytoma a beta-blocker without first giving an alpha-blocker!!!

• WHY? Epinephrine and Norepinephrine released by the adrenal medulla act on both alpha & beta receptors. In the absence of beta-2-mediated vasodilation, profound unopposed alpha-mediated vasoconstriction may lead to hypertensive crisis or pulmonary edema.
• Use: phenoxybenzamine beforehand or consider Labetalol (mixed alpha/beta adrenergic antagonist)

REFERENCES

1. Chapter 23: Hypertension. Symptom to Diagnosis: An Evidence-Based Guide, 3e
2. Myklejord DJ. Undiagnosed Pheochromocytoma: The Anesthesiologist Nightmare. Clinical Medicine and Research. 2004;2(1):59-62.