(264) Phentolamine Infusion for Pheochromocytoma Management in the Setting of Small Bowel Obstruction

Introduction: Hypertension is a hallmark symptom indicative of pheochromocytoma, a catecholamine producing neuroendocrine tumor. Initial symptom management of pheochromocytoma includes adrenergic blockade with oral alpha selective blockers. Phentolamine, an intravenous (IV) alternative, has not been extensively explored beyond the preoperative setting.

Description: A 76-year old female with a history of multiple abdominal surgeries was admitted for hypertensive urgency in addition to emesis for one week. Abdominal imaging revealed a small bowel obstruction (SBO) and a 7.5 cm right adrenal mass suggestive of pheochromocytoma. Due to concerns for absorption in the setting of persistent emesis and hypertension despite oral alpha selective blockers, options for IV agents to manage pheochromocytoma were explored. The patient was transferred to the surgical intensive care unit (ICU) where nicardipine, hydralazine, and labetalol proved to be ineffective. Based on preoperative indications and the mechanism of pure alpha blockade, a continuous phentolamine infusion was employed to target a systolic blood pressure (SBP) goal of < 160 mmHg. The infusion was titrated by 0.5-1 mg/hr every 15 minutes to achieve goal SBP. Phentolamine was titrated between the range of 0.5 mg/hr to 8.64 mg/hr for the 5 day duration of the infusion. Titration was guided by the degree of alpha blockade adequacy through the Roizen criteria in an effort to reduce mortality and the risk of cardiac events. The continuous phentolamine infusion was effective in hypertension management such that the patient was able to undergo an exploratory laparotomy with lysis of adhesions and gastrostomy placement. Thereafter, she tolerated full transition from phentolamine to doxazosin. Oral therapy was continued with plans for pheochromocytoma resection.

Discussion: To date, IV phentolamine is indicated preoperatively for patients with hypertension related to pheochromocytoma. Case reports have examined IV phentolamine as rescue therapy intraoperatively or in those with unknown pheochromocytoma and hypertension. Extrapolation of existing data to this critically ill patient lacking enteral access with absorption concerns demonstrates that a continuous phentolamine infusion can be used as an alternative to oral agents for adrenergic blockade in the ICU.