TY - CHAP M1 - Book, Section TI - Adrenergic Agonists & Antagonists A1 - Butterworth IV, John F. A1 - Mackey, David C. A1 - Wasnick, John D. PY - 2018 T2 - Morgan & Mikhail's Clinical Anesthesiology, 6e AB - KEY CONCEPTS Adrenergic agonists can be categorized as direct or indirect. Direct agonists bind to the receptor, whereas indirect agonists increase endogenous neurotransmitter activity. The primary effect of phenylephrine is peripheral vasoconstriction with a concomitant rise in systemic vascular resistance and arterial blood pressure. Clonidine decreases anesthetic and analgesic requirements and provides sedation and anxiolysis. Dexmedetomidine has a higher affinity for α2-receptors than clonidine. It has sedative, analgesic, and sympatholytic effects that blunt many of the cardiovascular responses seen during the perioperative period. Long-term use of these agents, particularly clonidine and dexmedetomidine, leads to super-sensitization and upregulation of receptors; with abrupt discontinuation of either drug, an acute withdrawal syndrome including hypertensive crisis can occur. Ephedrine is commonly used as a vasopressor during anesthesia. As such, its administration should be viewed as a temporizing measure while the cause of hypotension is determined and remedied. At low doses (0.5–3 mcg/kg/min), dopamine (DA) primarily activates dopaminergic receptors. Stimulation of these receptors (specifically, DA1 receptors) vasodilates the renal vasculature and promotes diuresis. Labetalol lowers blood pressure without reflex tachycardia because of its combination of α and β effects. Esmolol is an ultrashort-acting selective β1-antagonist that reduces heart rate and, to a lesser extent, blood pressure. Abrupt discontinuation of β-blocker therapy for 24 to 48 h may trigger a withdrawal syndrome characterized by hypertension, tachycardia, and angina pectoris. SN - PB - McGraw-Hill Education CY - New York, NY Y2 - 2024/03/28 UR - accessanesthesiology.mhmedical.com/content.aspx?aid=1161427055 ER -