Summary

In study session IV you have learnt

• Adrenergic receptors are divided into two general categories α and β. Each of these has been further subdivided into at least two subtypes.
• Alpha-1 agonist such as phenylephrine has effect of peripheral vasoconstriction with a concomitant rise in systemic vascular resistance and arterial blood pressure. Alpha-2 agonist such as clonidine and methyldopa are used for its antihypertensive (decreased systemic vascular resistance) and negative chronotropic effects.
• Direct stimulation of β1-receptors by epinephrine raises cardiac output and myocardial oxygen demand by increasing contractility and heart rate. Administration of epinephrine is the principal pharmacological treatment for anaphylaxis and during cardiac arrest. Volatile anesthetics, particularly halothane, potentiate the dysrhythmic effects of epinephrine.
• Ephedrine is commonly used as a vasopressor during anesthesia. It does not decrease uterine blood flow. This makes it the preferred vasopressor for most obstetric uses.
• Beta 2-Agonists such as albuterol are used to treat reactive airway disease.
• Phentolamine produces a competitive (reversible) blockade of alpha one receptor and responsible for peripheral vasodilation and a decline in arterial blood pressure. The drop in blood pressure provokes reflex tachycardia.
• Adverse effects of beta blocker are life-threatening bradycardia, even asystole, may occur with β-blockade, and decreased contractility may precipitate CHF in patients with compromised cardiac function
• Calcium channel blockers promote vasodilator activity (and reduce blood pressure) by reducing calcium influx into vascular smooth muscle cells. Calcium channel blockers potentiate the hypotensive effects of volatile anesthetics.
• Digitalis has the unique characteristic of increasing contractility (positive inotropy) while decreasing heart rate (negative chronotropy). Indications of digoxin include congestive heart failure, atrial fibrillation and paroxysmal atrial tachycardia.
• Diuretic agents are drugs that increase renal excretion of water and solute. Major purposes of diuretic therapy are to decrease fluid volume of the body, and to adjust the water and electrolyte balance. Diuretics are often used in the management of pathological conditions such as edema (e.g. in congestive heart failure and certain renal diseases) and hypertension.