Anesthetic management of Pheochromocytoma

Discuss the pre-anesthetic preparation, anaesthetic goals and intra-operative management of a 30yr old female patient with diagnosis of pheochromocytoma scheduled for excision of adrenal tumour?

Pre-anesthetic preparation

Investigations

Routine laboratory are the complete blood cell count( elevated hematocrit consistent with a reduced intravascular volume and hemoconcentration)., ECG( Left ventricular hypertrophy and nonspecific T-wave changes are two of the more common ECG findings..Chest radiography may reveal cardiomegaly,

 Standardized imaging methods such as computed tomography and magnetic resonance imaging are used in the noninvasive localization of these tumors.

Ultrasound and magnetic resonance imaging are especially useful in pregnant patients.

¹³¹I-Metaiodobenzylguanidine scintigraphy is also effective in localizing recurrent or extra-adrenal masses.

 Biochemical determination of free catecholamine concentration and catecholamine metabolites in the urine is the most common screening test used to establish the diagnosis of pheochromocytoma. Urinary vanillylmandelic acid and unconjugated norepinephrine and epinephrine levels are measured in a 24-hour urine collection and are expressed as a function of the creatinine clearance. Excess production of catecholamines is diagnostic for pheochromocytoma

To rule out familial association, as this tumour is sometimes part of the pluriglandular-neoplastic syndrome known as multiple endocrine adenoma type IIa or type IIb and is manifested as an autosomal dominant trait. Type IIa consists of medullary carcinoma of the thyroid, parathyroid adenoma or hyperplasia, and pheochromocytoma. What used to be called type IIb is now often called pheochromocytoma in association with phakomatoses such as von Recklinghausen's neurofibromatosis and von Hippel-Lindau disease with cerebellar hemangioblastoma.

A reduction in mortality associated with resection of pheochromocytoma (from 40% to 60% to the current 0% to 6%) occurred when α-adrenergic receptor blockade was introduced as preoperative and preprocedure preparatory therapy for such patients.
Adrenergic receptor blockade with prazosin or phenoxybenzamine restores plasma volume by counteracting the vasoconstrictive effects of high levels of catecholamines. This re-expansion of fluid volume is often followed by a decrease in hematocrit. Phenoxybenzamine, is initially  given in doses of 20 to 30 mg/70 kg orally because of variable sensitivity once or twice a day. And increased 60 to 250 mg/day depending on requirement. The efficacy of therapy is judged by the reduction in symptoms (especially sweating) and stabilization of BP.
 For patients who have carbohydrate intolerance because of inhibition of insulin release mediated by α-adrenergic receptor stimulation, α-adrenergic receptor blockade may reduce fasting blood sugar levels. For patients who exhibit ST-T changes on the ECG, long-term preoperative and preprocedure α-adrenergic receptor blockade (1 to 6 months) is tried,,adrenergic receptor blockade with propranololis used for patients who have persistent arrhythmias or tachycardia e. β-Adrenergic receptor blockade should not be used without concomitant α-adrenergic receptor blockade lest the vasoconstrictive effects of the latter go unopposed and thereby increase the risk for dangerous hypertension.
The optimal duration of preoperative therapy with phenoxybenzamine can vary from 10 to 14 days, as judged by the time needed to stabilize BP and ameliorate symptoms. Some recommend using the following criteria:

1.         No in hospital BP more than 160/90 mm of hg should be present 48hrs before surgery.

	2.	Orthostatic hypotension should be present, but BP on standing should not be lower than 80/45 mm Hg.
	3.	The ECG should be free of ST-T changes that are not permanent.
	4.	No more than one premature ventricular contraction (PVC) should occur every 5 minutes

Anesthetic goals

1.       Good preoperative optimization with controlled vitals.

2.      Maitaining a deep level of anesthesia intraoperatively

3.      Strict and meticulous monitoring.

4.      Managing hypertensive and hypotensive episode crisis promptly

5.      .Meticulous fluid management.

Anesthetic Management

Although there is no clear advantage to one anesthetic technique over another, drugs that are known to liberate histamine are avoided.

Because of the potential for ventricular irritability, halothane is not administered

Monitoring is done with Pulse-oximetry,ECG,non-invasive blood pressure capnography and if required invasive monitoring.

 A potent sedative-hypnotic, in combination with an opioid analgesic, is used for induction.

 It is extremely important to achieve an adequate depth of anesthesia before proceeding with laryngoscopy to minimize the sympathetic nervous system response to this maneuver.

Maintenance is provided with an opioid analgesic and a potent inhalation agent. Manipulation of the tumor may produce marked elevations in blood pressure. Acute hypertensive crises are treated with intravenous infusions of nitroprusside or phentolamine or any vasodilator. Phen-tolamine is a short-acting α-adrenergic antagonist that may be given as an intravenous bolus (2 to 5 mg) or by continuous infusion.

Tachydysrhythmia is controlled with intravenous boluses of propranolol (1-mg increments) or by a continuous infusion of the ultrashort-acting selective β₁-adrenergic antagonist esmolol. The disadvantage of long-acting beta-blockers may be persistence of bradycardia and hypotension after the tumor is removed..

 Magnesium sulfate given as an infusion with intermittent boluses has successfully controlled blood pressure Nicardipine, nitroglycerin, diltiazem, fenoldopam, and prostaglandin E₁ can all been used.

The reduction in blood pressure that may occur after ligation of the tumor's venous supply which  can be dangerously abrupt and should be anticipated through close communication with the surgical team. Restitution of any intravascular fluid deficit is the initial therapy in this situation. After replenishment of the intravascular volume, if the patient remains hypotensive, phenylephrine is administered.

After surgery, catecholamine levels return to normal over several days. Postoperatively,  meticulous monitoring for  hypertension is done  for 1 to 3 days but it may take 10 days to become normotensive.