Epinephrine. Effects, Indications, Dosing.

Epinephrine (Adrenaline) is naturally occurring catecholamine. It is is the prototype sympathomimetic. Epinephrine is synthesized, stored, and released from the adrenal medulla. Through activation of a-adrenergic receptors , b1 and b2 receptors regulates:

myocardial contractility
heart rate
vascular and bronchial smooth muscle tone
glandular secretions
metabolic processes such as glycogenolysis and lipolysis

Not administered orally as it is rapidly metabolized in the gastrointestinal mucosa and liver. Therefore, epinephrine is administered subcutaneously, intramuscularly (Epipen), or intravenously.

Indications

allergic reactions/anaphylaxis
treatment of severe asthma and bronchospasm
during cardiopulmonary resuscitation
during periods of hemodynamic instability to enhance myocardial contractility and increase vascular resistance
during
weaning from cardiopulmonary bypass
increasing cardiac output in sepsis
as part of local anesthetic solutions to decrease systemic absorption

Airway Smooth Muscle

Smooth muscles of the bronchi are relaxed by activation of b2 receptors. In the presence of b adrenergic blockade, epinephrine instead induces bronchoconstriction

Cardiovascular Effects

Stimulation of a1 and a2 receptors leads to arteriolar vasoconstriction and pulmonary artery vasoconstriction. b2 Receptor stimulation leads to vasodilation, predominantly in the skeletal muscles but b2 receptors are more sensitive to lower epinephrine doses while effects on a1 receptors predominate at higher doses. Initial tachycardia may be followed by heart rate decreases due to baroreceptor reflexes.

Epinephrine increases heart rate which also increases the likelihood of cardiac dysrhythmias. Repeated doses of epinephrine produce tachyphylaxis, myocardial oxygen consumption is increased. Coronary blood flow is enhanced by epinephrine.

Metabolic Effects

Increases liver glycogenolysis and adipose tissue lipolysis is due to epinephrine-induced activation of triglyceride lipase.

Increase plasma concentrations of glucose, cholesterol, phospholipids, and low-density lipoproteins.

Inhibits release of insulin.

Epinephrine-induced hyperlactemia.

Gastrointestinal and Genitourinary Effects

Produces relaxation of gastrointestinal smooth muscle.

Relaxes the detrusor muscle of the bladder (b-receptor)

Contracts the trigone and sphincter muscles (a-receptor)

Decreases hepatosplanchnic oxygen exchange and lactate clearance.

Coagulation

Accelerates coagulation, platelet aggregation and increases the total leukocyte count but causes eosinopenia.