Phentolamine to make the diagnosis of Pheochromocytoma

Q: How the Phentolamine is used to make the diagnosis of Pheochromocytoma? 

Answer: 

Since advances in laboratory tests, the use of phentolamine to diagnose pheochromocytoma has become more of academic interest. Said that, it is still of importance for a physician to know its modus operandi for the sake of better comprehension of the disease.

If a physician decides to run a phentolamine test to evaluate pheochromocytoma, it should ideally be performed in an ICU setting as it may mark life-threatening hemodynamic instability. The patient should be put in a supine position in a comfortable non-stimulus environment. Blood pressure should be monitored every 10 minutes for at least 30 minutes, and till patient is at his known hypertensive level. A drop in blood pressure more than 35 mm Hg in systolic, and more than 25 mm Hg in diastolic is considered a positive response. If blood pressure does not change, or decrease is not more than 35 mm Hg in systolic and more than 25 mm Hg in diastolic, the test is considered negative. This is not a confirmatory teat but has a good predictive value. 

With a rapid intravenous injection, the response is expected to be brisk. Blood pressure should be monitored immediately after IV push of phentolamine and every 30 seconds for 3 minutes, and then every minute for 7 minutes. The maximum response is generally achieved within 2 minutes. Phentolamine effect lasts for 15 to 30 minutes.

#cardiology
#procedures


References:

1. Marik PE and Varon J. Hypertensive Crises: challenges and management. Chest. 2007;131:1949-1962. 

2.  McMillian WD, Trombley BJ, Charash WE, et al. Phentolamine Continuous infusion in a patient with pheochromocytoma. Am J Health-Syst Pharm. 2011;68:130-134.