Hypotensive Agents

Hypotensive Agents

A multitude of drugs are capable of lowering blood pressure, including volatile anesthetics, sympathetic antagonists and agonists, calcium channel block-ers, β-blockers, and angiotensin-converting enzyme inhibitors.

In patients with “older” vasculature, the wave arrives sooner, being conducted back by the noncompli-ant vasculature during late systole, which causes an increase in cardiac workload and a decrease in dia-stolic pressure (Figure 15–1). Thus, older patientsdevelop increased systolic pressure and decreased diastolic pressure.

Widened pulse pressures (the difference between systolic and diastolic pressures) have been associated with both increased incidence of postop-erative renal dysfunction and increased risk of cere-bral events in patients undergoing coronary bypass

surgery. Consequently, control of blood pressure is essential to mitigate postoperative morbidity, espe-cially as patients of advanced vascular age present for surgery.

β-Blocker therapy should be maintained peri-operatively in patients who are being treated with β-blockers as a part of their routine medical regimen. Furthermore, according to the American College of Cardiology, β-blockers are also of potential benefit to patients with more than one cardiac risk factor, espe-cially those who are undergoing vascular surgery. However, the routine administration of high-dose β-blocker therapy may, in the absence of dose titra-tion, be harmful in patients not taking β-blockers. The American College of Cardiology/American Heart Association guidelines for β-blocker use peri-operatively should be closely followed. Adherence to such guidelines is used by third parties as a “quality” performance indicator for anesthesia delivery. Thus, anesthesia providers should periodically review recommendations regarding β-blocker therapy, as guidelines evolve as new evidence becomes available and older evidence is refuted. β-Blockers (esmolol, metoprolol, and others) were previously discussed for the treatment of transient perioperative hyper-tension and are routinely used by anesthesia provid-ers.

Along with increased vascular age, diastolic dysfunction is often underestimated in patients, as it can present in individuals with preserved sys-tolic function. Acute diastolic heart failure can develop in the perioperative period secondary to hypertensive crisis. Diastolic dysfunction occurs due to the inability of the heart to relax effectively. Failure to actively sequester calcium ion into the sarcoplasmic reticulum (an energy-dependent process) impedes relaxation. Acute hypertension can produce diastolic dysfunction perioperatively, leading to elevated left ventricular end-diastolic pressures, myocardial ischemia, and pulmonary edema. Consequently, as increasing numbers of patients have diastolic dysfunction, tight control of blood pressure perioperatively is essential for safe anesthetic practice.

Blood pressure is essentially the product of car-diac output and systemic vascular resistance. Agents that lower blood pressure either reduce the force of myocardial contraction and/or produce vasodilata-tion of the arterial and venous capacitance vessels. Agents used to lower blood pressure include nitro-vasodilators, calcium antagonists, dopamine ago-nists, anesthetic agents, and angiotensin-converting enzyme inhibitors. β-Blockers have been previously discussed.