EPINEPHRINE

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Epinephrine, also known as adrenaline, is a naturally occurring catecholamine that has multiple applications in anesthesia and perioperative care. The importance of epinephrine in anesthesia can be attributed to its various effects, which include vasoconstriction, bronchodilation, and increased inotropy and chronotropy. Key applications of epinephrine in anesthesia include:

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1. Prolongation of local anesthetic action: Epinephrine is often added to local anesthetic solutions as a vasoconstrictor. By causing vasoconstriction at the injection site, epinephrine reduces local blood flow, decreasing the rate of anesthetic absorption and prolonging its duration of action. This can lead to a more effective and longer-lasting regional blockade.

2. Hemostasis: Epinephrine's vasoconstrictive properties are useful in achieving hemostasis during surgery. By constricting blood vessels, epinephrine reduces bleeding and facilitates a clearer surgical field. This can improve surgical outcomes and reduce the risk of complications associated with excessive blood loss.

3. Treatment of anaphylaxis and allergic reactions: Epinephrine is the first-line treatment for severe allergic reactions and anaphylaxis, which can occur during the perioperative period due to exposure to medications or other allergens. It acts rapidly to counteract the life-threatening symptoms of anaphylaxis, such as hypotension, bronchoconstriction, and angioedema.

4. Management of cardiac arrest: Epinephrine is a key component of advanced cardiac life support (ACLS) protocols for managing cardiac arrest. It increases coronary and cerebral blood flow, enhances myocardial contractility, and stimulates spontaneous contractions, all of which can contribute to the return of spontaneous circulation (ROSC).

5. Treatment of hypotension: Epinephrine can be used to treat perioperative hypotension, particularly when it is refractory to other vasopressor agents. It increases systemic vascular resistance, heart rate, and contractility, effectively raising blood pressure.

6. Bronchodilation: Epinephrine's bronchodilatory effects can be beneficial in the management of perioperative bronchospasm or asthma exacerbations. It relaxes bronchial smooth muscle, improving airway patency and oxygenation.

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Here are the main steps in epinephrine's mechanism of action:

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1. Binding to adrenergic receptors: Epinephrine binds to and activates α1-, α2-, β1-, and β2-adrenergic receptors found in the smooth muscle cells of blood vessels, the heart, bronchi, and other tissues.

2. Vasoconstriction: Activation of α1-adrenergic receptors on vascular smooth muscle cells leads to vasoconstriction, primarily in arterioles and to a lesser extent in veins. This effect increases systemic vascular resistance and blood pressure, and can also reduce local blood flow when used as a local vasoconstrictor with local anesthetics.

3. Cardiac stimulation: Epinephrine's action on β1-adrenergic receptors in the heart increases the force of cardiac muscle contractions (positive inotropic effect) and the heart rate (positive chronotropic effect). This results in an increased cardiac output, which contributes to the elevation of blood pressure and improves perfusion to vital organs.

4. Bronchodilation: Activation of β2-adrenergic receptors in bronchial smooth muscle cells causes relaxation of these cells and bronchodilation. This effect can help alleviate bronchospasm in conditions such as asthma and chronic obstructive pulmonary disease (COPD).

5. Glycogenolysis and lipolysis: Epinephrine stimulates glycogenolysis in the liver and skeletal muscles and lipolysis in adipose tissue through the activation of β-adrenergic receptors. These metabolic effects increase the availability of glucose and fatty acids as energy sources during periods of stress or increased energy demand.

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                                                                                         Key points about Epinephrine

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• Direct agonist at α1, α2, β1 and β2 receptors

 

• Main clinical uses: Treatment during cardiopulmonary resuscitation, treatment of life-threatening allergic reactions/anaphylaxis, treatment of severe asthma, bronchospasms, and during cardiopulmonary bypass.

 

• DOSE-DEPENDENT increases in contractility, HR, and SVR.

 

• At lower doses, predominant beta effects (cardiac stimulation and vasodilation > promotes forward flow).

 

• At higher doses, predominant alpha effects (vasoconstriction > increase in SVR may decrease cardiac output).

 

• Positive inotropic, chronotropic, dromotropic, and lusitropic effects.

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• It is an effective bronchodilator and mast cell stabilizer (useful for bronchospasm and anaphylactic reactions).

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• May produce organ ischemia due to vasoconstriction (monitor kidney function and extremity perfusion).

 

• May produce myocardial ischemia and pulmonary hypertension.

 

• Epinephrine has the most effects on metabolism of all catecholamines. Increases plasma glucose and lactate (effect may be accentuated in diabetics).

 

• Stimulates Na+/K+ ATPase pump which decreases plasma potassium as more K+ moves inside the cells.

 

• In the presence of beta-blockers, epinephrine alpha effects are increased and may lead to bronchoconstriction from stimulation of bronchial alpha receptors.

 

• Epinephrine is usually added to local anesthetics to decrease systemic absorption and prolong duration of action.

 

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