Epinephrine is an endogenous catecholamine syn-thesized in the adrenal medulla. Direct stimulation of β1-receptors of the myocardium by epinephrine raises blood pressure, cardiac output, and myocar-dial oxygen demand by increasing contractility and heart rate (increased rate of spontaneous phase IV depolarization). α1-stimulation decreases splanch-nic and renal blood flow but increases coronary perfusion pressure by increasing aortic diastolic pressure. Systolic blood pressure rises, although β2-mediated vasodilation in skeletal muscle may lower diastolic pressure. β2-stimulation also relaxes bron-chial smooth muscle.
Administration of epinephrine is the princi-pal pharmacological treatment for anaphylaxis and can be used to treat ventricular fibrillation. Com-plications include cerebral hemorrhage, coronary ischemia, and ventricular dysrhythmias. Volatile anesthetics, particularly halothane, potentiate the dysrhythmic effects of epinephrine.
In emergency situations (eg, cardiac arrest and shock), epinephrine is administered as an intrave-nous bolus of 0.05–1 mg, depending on the severity of cardiovascular compromise. In major anaphylac-tic reactions, epinephrine should be used at a dose of 100–500 mcg (repeated, if necessary) followed by infusion. To improve myocardial contractil-ity or heart rate, a continuous infusion is prepared (1 mg in 250 mL [4 mcg/mL]) and run at a rate of 2–20 mcg/min. Epinephrine is also used to reduce bleeding from the operative sites. Some local anes-thetic solutions containing epinephrine at a con-centration of 1:200,000 (5 mcg/mL) or 1:400,000 (2.5 mcg/mL) are characterized by less systemic absorption and a longer duration of action. Epi-nephrine is available in vials at a concentration of 1:1000 (1 mg/mL) and prefilled syringes at a con-centration of 1:10,000 (0.1 mg/mL [100 mcg/mL]). A 1:100,000 (10 mcg/mL) concentration is available for pediatric use.
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