Hypertension: Intraoperative Management

INTRAOPERATIVE MANAGEMENT

Objectives

The overall anesthetic plan for a hypertensive patient is to maintain an appropriate stable blood pressure range. Patients with borderline hypertension may be treated as normotensive patients. Those with long-standing or poorly controlled hypertension, how-ever, have altered autoregulation of cerebral blood flow; higher than normal mean blood pressures may be required to maintain adequate cerebral blood flow. Because most patients with long-standing hypertension are assumed to have some element of CAD and cardiac hypertrophy, excessive blood pressure elevations are undesirable. Hypertension, particularly in association with tachycardia, can precipitate or exacerbate myocardial ischemia, ventricular dysfunction, or both. Arterial blood pressure should generally be kept within 20% of preoperative levels. If marked hypertension (>180/ 120 mm Hg) is present preoperatively, arterial blood pressure should be maintained in the high-normal range (150–140/90–80 mm Hg).

Monitoring

Most hypertensive patients do not require special intraoperative monitors. Direct intraarterial pres-sure monitoring should be reserved for patients with wide swings in blood pressure and those undergo-ing major surgical procedures associated with rapid or marked changes in cardiac preload or afterload.

Electrocardiographic monitoring should focus on detecting signs of ischemia. Urinary output should generally be monitored with an indwelling urinary catheter in patients with a preexisting renal impair-ment who are undergoing procedures expected to last more than 2 hr. When invasive hemodynamic monitoring is used, reduced ventricular compli-ance  is often apparent in patients with ventricular hypertrophy; these patients may require more intravenous fluid to produce a higher filling pressure to maintain adequate left ventricular end-diastolic volume and cardiac output. Volume administration in patients with decreased ventricu-lar compliance can also result in elevated pulmonary arterial pressures and pulmonary congestion.

Induction

Induction of anesthesia and endotracheal intubation are often associated with hemodynamic instability in hypertensive patients. Regardless of the level of preoperative blood pressure control, manypatients with hypertension display an accentuated hypotensive response to induction of anesthesia, fol-lowed by an exaggerated hypertensive response to intubation. Many, if not most, antihypertensive agents and general anesthetics are vasodilators, cardiac depressants, or both. In addition, many hypertensive patients present for surgery in a volume-depleted state. Sympatholytic agents attenuate the normal pro-tective circulatory reflexes, reducing sympathetic tone and enhancing vagal activity.

Up to 25% of hypertensive patients may exhibit severe hypertension following endotracheal intuba-tion. Prolonged laryngoscopy should be avoided. Moreover, intubation should generally be performed under deep anesthesia (provided hypotension can be avoided). One of several techniques may be used before intubation to attenuate the hypertensive response:

·        Deepening anesthesia with a potent volatile agent

·        Administering a bolus of an opioid (fentanyl, 2.5–5 mcg/kg; alfentanil, 15–25 mcg/kg; sufentanil, 0.5–1.0 mcg/kg; or remifentanil, 0.5–1 mcg/kg).

·        Administering lidocaine, 1.5 mg/kg intravenously, intratracheally, or topically in the airway

·        Achieving β-adrenergic blockade with esmolol, 0.3–1.5 mg/kg; metoprolol 1–5 mg;or labetalol, 5–20 mg.

Choice of Anesthetic Agents

A. Induction Agents

The superiority of any one agent or technique over another has not been established. Propofol, barbi-turates, benzodiazepines, and etomidate are equally safe for inducing general anesthesia in most hyper-tensive patients. Ketamine by itself can precipitate marked hypertension; however, it is almost never used as a single agent. When administered with a small dose of another agent, such as a benzodiaz-epine or propofol, ketamine’s sympathetic stimulat-ing properties can be blunted or eliminated.

B. Maintenance Agents

Anesthesia may be safely continued with volatile agents (alone or with nitrous oxide), a balanced technique (opioid + nitrous oxide + muscle relax-ant), or a total intravenous technique. Regardless of the primary maintenance technique, addition of a volatile agent or intravenous vasodilator gener-ally allows convenient intraoperative blood pressure control.

C. Muscle Relaxants

With the possible exception of large bolus doses of pancuronium, any muscle relaxant can be used. Pancuronium-induced vagal blockade and neu-ral release of catecholamines could exacerbate hypertension in poorly controlled patients, but, if given slowly, in small increments, pancuronium is unlikely to cause medically important increases in heart rate or blood pressure. Moreover, pan-curonium can be useful in offsetting excessive vagal tone induced by opioids or surgical manipulations. Hypotension following large (intubating) doses of atracurium may be accentuated in hypertensive patients.

D. Vasopressors

Hypertensive patients may display an exagger-ated response to both endogenous catecholamines (from intubation or surgical stimulation) and exogenously administered sympathetic agonists. If a vasopressor is necessary to treat excessive hypotension, a small dose of a direct-acting agent, such as phenylephrine (25–50 mcg), may be use-ful. Patients taking sympatholytics preoperatively may exhibit a decreased response to ephedrine. Vasopressin as a bolus or infusion can also be employed to restore vascular tone in the hypoten-sive patient.

Intraoperative Hypertension

Intraoperative hypertension not responding to an increase in anesthetic depth (particularly with a vol-atile agent) can be treated with a variety of parenteral agents (Table 21–7). Readily reversible causes— such as inadequate anesthetic depth, hypoxemia, or hypercapnia—should always be excluded before initiating antihypertensive therapy. Selection of a hypotensive agent depends on the severity, acute-ness, and cause of hypertension; the baseline ven-tricular function; the heart rate; the presence of bronchospastic pulmonary disease; and the anes-thetist’s familiarity with each of the drug options. β-Adrenergic blockade alone or as a supplement isa good choice for a patient with good ventricular function and an elevated heart rate, but is relatively contraindicated in a patient with bronchospastic disease. Metoprolol, esmolol, or labetolol are read-ily used intraoperatively. Nicardipine or clevidipine may be preferable to β-blockers for patients with bronchospastic disease. Nitroprusside remains the most rapid and effective agent for the intraopera-tive treatment of moderate to severe hypertension. Nitroglycerin may be less effective, but is also use-ful in treating or preventing myocardial ischemia. Fenoldopam, a dopamine agonist, is also a useful hypotensive agent; furthermore, it increases renal blood flow. Hydralazine provides sustained blood pressure control, but also has a delayed onset and can cause reflex tachycardia. The latter is not seen with labetalol because of a combined α- and β-adrenergic blockade.