General Medical Information

Hypertension

David M. Barrs

Antihypertensive medications should be continued to the morning of surgery and resumed immediately postoperatively. b-Blocking agents should be continued until surgery and resumed immediately postoperatively, because sudden cessation can produce a withdrawal syndrome with sinus tachycardia, hypertension, myocardial ischemia, or tachyarrhythmias. The symptoms may mimic a variety of cardiac abnormalities, but they respond rapidly to resumption of propranolol, which may be given intravenously 1 to 2 mg every 5 to 10 minutes until the condition improves. Clonidine withdrawal syndrome can be character-ized by a hypertensive crisis that may need i.v. nitroprusside or phentolamine for control. Monoamine oxidase inhibitors and guanethidine should be discontinued 2 weeks before surgery because of the possibility of severe drug interactions or interference with circulatory reflexes. Consideration should be given to withholding diuretic therapy for 1 to 7 days before surgery to enable potassium deficits and volume depletion to be corrected before surgery.

All anesthetic agents are vasodilators and negative ionotropes, which may create the necessity for fluid infusion in excess of fluid losses during surgery. Pharmacologic agents may be needed to control blood pressure during surgery. On emergence from anesthesia, sympathetic tone in the vessels is restored and blood pressure can rise significantly. Postoperative hypertensive events are defined as systolic blood pressure greater than 200 mm Hg, a rise in systolic blood pressure greater than 50 mm Hg, or a diastolic blood pressure greater than 100 mm Hg.

In postoperative hypertension, it is extremely important to search for a cause rather than simply to treat the hypertension with pharmacologic agents. The differential diagnosis of postoperative hypertension should include hypervolemia, ventilatory or respiratory failure, inadequate analgesia or discomfort, residual effects of anesthesia or intraoperative pressor agents, anesthetic-induced hypothermia and shivering, distended stomach or bladder, or manifestations of preexisting hypertension. Treatable causes of postoperative hypertension should be corrected before pharmacologic agents are given, because severe hypotension may result if simultaneous antihypertensive medications and treatment of the underlying cause of hypertension are undertaken.

Prolonged or extreme postoperative hypertension may lead to myocardial failure or increased risk of intracranial bleeding in neurotologic or skull-base procedures. In urgent situations, the pharmacologic agent of choice is nitroprusside.