Perioperative Management Of Pheochromocytomas

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It is important for patients to have fully repleted intravascular volumes prior to surgery. Some surgeons admit patients for intravenous fluids one day prior to surgery and predonate blood for autologous transfusion and infuse two units of blood within 12 hours preoperatively.61 It is not usually necessary.

All adrenal masses of unknown pathology should be managed with the extreme care rendered to a pheochromocytoma. Constant invasive blood pressure monitoring requires an arterial line.47 A central venous pressure line is sometimes necessary to monitor fluid replacement. A pulmonary artery (Swan-Ganz) line is inserted in selected high-risk patients with congestive heart failure or coronary artery disease to further optimize fluid replacement. Constant electrocardiographic monitoring is mandatory. Severe hypertension is frequently encountered, even in "fully blocked" patients, on bladder catheter-ization, intubation, surgical incision, and pneu-moperitoneum for laparoscopy or during manipulation of the tumor.65 During laparoscopic surgery, catecholamine release is especially stimulated by pneumoperitoneum and by tumor manipulation.66 Therefore, all medication that may be required should be ready in advance. Laparoscopic operations, however, cause less fluctuation of cate-cholamine levels than open operations.

A balanced anesthetic technique is usually used. Agents such as intravenous propofol, enflurane, isoflurane, sufentanil, and nitrous oxide appear to be effective and safe.67,68 Muscle relaxants with the least hypertensive effect are used (eg, vecuronium).47 Hypertension is managed by increasing the depth of anesthesia and by vasodilators for blood pressure over 160/90 mm Hg. The infusion rates are adjusted to control blood pressure. Catecholamine levels drop abruptly on clipping of the adrenal vein; therefore, the vasodilator infusion is stopped immediately before ligation of the adrenal vein. This reduces the chance of sudden hypotension after resection of the pheochromocytoma.

Nicardipine, a calcium channel blocker, is effective as an intravenous infusion in doses of 2 to 6 p,g/kg/minute. Nicardipine was successfully used as the sole intraoperative vasodilating agent in one series of 70 patients and another series of 19 patients.56,69

Sodium nitroprusside intravenous infusion is effective in managing hypertensive episodes. Advantages to its use include its short duration of action and its widespread familiarity. The usual dose is 0.3 to 10 p,g/kg/minute. The maximal infusion rate should be given for no longer than 10 minutes because with prolonged (over 6 hours) nitroprusside infusion rates above 2 p,g/kg/minute, cyanide may accumulate to toxic concentrations. Coadministration of sodium thiosulfate (1 g/100 mg nitroprus-side) prevents cyanide accumulation.70

Nitroglycerin intravenous infusion is effective for treating perioperative hypertension. The required dosage ranges from 5 to 100 p,g/minute. However, nitroglycerin adheres to polyvinyl chloride tubing, so appropriate dilutions, dosing, and infusion sets must be used. Side effects include headache and hypotension. Methemoglobinemia has rarely occurred during prolonged, high-dose infusions and is manifested by cyanosis in the presence of a normal arterial oxygen partial pressure. The treatment for methemoglobine-mia consists of stopping the nitroglycerin and giving methylene blue, 1 to 2 mg/kg intravenously.

Phentolamine mesylate (Regitine) is a short-acting a-adrenergic blocker with an intravenous halflife of 19 minutes. Bolus doses of 5 to 15 mg (1 to 3 mg for children) are administered intravenously for blood pressure control. Phentolamine may also be given as an intravenous infusion at a rate of 0.5 to 1 mg/minute. Side effects include hypotension, tachycardia, cardiac arrhythmias, nasal stuffiness, nausea, and vomiting.

Lidocaine 50 to 100 mg intravenously may be used to treat cardiac ventricular arrhythmias. Atrial tachyarrhythmias may be treated with intravenous boluses of atenolol 1 mg or by constant infusion of a short-acting P-blocker such as esmolol.

Immediately after resection of a pheochromocy-toma, severe hypotension and cardiovascular collapse can occur, particularly in patients with norepi-nephrine-secreting tumors. This hypotension is largely owing to desensitization of a1-adrenergic receptors, persistence of antihypertensives, and low plasma volume. Preoperative preparation with calcium channel blockers and/or alpha-blockade and forced hydration attenuate this effect. Treatment of shock consists of large volumes of intravenous saline or colloid. Intravenous norepinephrine (Levophed) is sometimes required in high doses. Immediately following resection of the pheochro-mocytoma, intravenous 5% dextrose should be infused at a constant rate of about 100 mL/hour to prevent hypoglycemia that is otherwise frequently encountered postoperatively.

Labetalol infusion is not recommended for perioperative or intraoperative management of pheochro-mocytoma because it aggravates postresection hypotension, owing to its long half-life. It may also paradoxically initially aggravate hypertension (see above). Additionally, labetalol inhibits MIBG uptake and causes false elevations in urinary catecholamine determinations.71,72 Diazoxide (Hyperstat) infusion is also not recommended for hypertension management. Atropine premedication may cause arrhythmias and hypertension despite preoperative a-adren-ergic blockade.8

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