Epinephrine: Uses, Mechanism, Dosage, and Side Effects

Epinephrine, also known as adrenaline, is a naturally occurring catecholamine and a potent adrenergic medication with important effects on the respiratory and cardiovascular systems. It stimulates alpha and beta receptors, allowing it to produce vasoconstriction, bronchodilation, increased heart rate, and increased myocardial contractility.

These actions make epinephrine useful in conditions ranging from anaphylaxis and cardiac arrest to upper-airway edema and selected respiratory emergencies.

Understanding its receptor activity, formulations, routes of administration, clinical uses, and adverse effects is essential for recognizing how and why the medication is used.

 

What Is Epinephrine?

Epinephrine is both a hormone produced naturally by the body and a medication used to produce sympathetic nervous system effects. It is secreted primarily by the adrenal medulla during periods of stress, exercise, fear, hypoglycemia, or other situations that activate the body’s sympathetic response.

As a medication, epinephrine is classified as a sympathomimetic or adrenergic agonist. It acts on several adrenergic receptor types rather than selectively stimulating only one. Its major receptor effects involve:

• Alpha-1 receptors
• Beta-1 receptors
• Beta-2 receptors

Because these receptors are found in different tissues, epinephrine can influence the airways, heart, systemic blood vessels, pulmonary circulation, and mucosal tissues at the same time.

This broad receptor activity explains why epinephrine can be useful in emergencies involving multiple body systems. It also explains why the medication can produce significant cardiovascular side effects.

Adrenergic Receptors and Epinephrine

The effects of epinephrine are best understood by examining the adrenergic receptors it stimulates.

Adrenergic receptors respond to catecholamines such as epinephrine and norepinephrine. These receptors are part of the sympathetic nervous system and help regulate the body’s response to physiologic stress.

Alpha-1 Receptors

Alpha-1 receptors are located primarily in vascular smooth muscle. When epinephrine stimulates these receptors, vascular smooth muscle contracts. The result is vasoconstriction.

Alpha-1 stimulation can:

• Increase systemic vascular resistance
• Increase arterial blood pressure
• Reduce blood flow to swollen mucosal tissues
• Decrease airway edema
• Reduce bleeding through local vasoconstriction

Note: This vasoconstricting action is especially important in upper-airway disorders such as croup and postextubation laryngeal edema.

Beta-1 Receptors

Beta-1 receptors are located primarily in cardiac tissue. Stimulation increases the activity of the heart.

Major effects include:

• Increased heart rate
• Increased myocardial contractility
• Increased conduction through the cardiac electrical system
• Increased cardiac excitability
• Increased myocardial oxygen consumption

Note: These effects can be beneficial when cardiac activity is severely depressed, but they can also produce tachycardia and arrhythmias.

Beta-2 Receptors

Beta-2 receptors are found in bronchial smooth muscle and other tissues. Stimulation of beta-2 receptors causes relaxation of bronchial smooth muscle, producing bronchodilation.

Beta-2 activation can therefore:

• Increase airway diameter
• Decrease bronchial smooth-muscle tone
• Reduce airway resistance
• Improve airflow during bronchospasm

Note: Although epinephrine can act as a bronchodilator, its lack of beta-2 selectivity makes medications such as albuterol more appropriate for routine treatment of most bronchospastic disorders.

Mechanism of Action

The beta effects of epinephrine occur through a G protein-linked receptor system. When epinephrine binds to beta receptors on the surface of a cell, a G protein is activated. This stimulates the enzyme adenylyl cyclase, which increases intracellular cyclic adenosine monophosphate, commonly known as cAMP.

In bronchial smooth muscle, increased cAMP contributes to relaxation by altering intracellular calcium activity and reducing the activity of myosin light-chain kinase.

The final result is relaxation of bronchial smooth muscle and bronchodilation.

Alpha-receptor activity works differently. Alpha-1 stimulation causes contraction of vascular smooth muscle, leading to vasoconstriction. These two mechanisms explain why epinephrine can simultaneously relax bronchial smooth muscle while constricting blood vessels.

Epinephrine as a Catecholamine

Epinephrine belongs to a group of compounds known as catecholamines. Other catecholamines include norepinephrine and dopamine. Catecholamines generally have a rapid onset of action but relatively short duration because they are rapidly metabolized.

One important enzyme responsible for catecholamine metabolism is catechol O-methyltransferase, or COMT. Monoamine oxidase, or MAO, also contributes to catecholamine degradation.

Rapid metabolism explains why epinephrine can act quickly but does not provide prolonged bronchodilation. Catecholamines are also poorly suited for oral administration because extensive metabolism in the gastrointestinal tract and liver greatly reduces their effectiveness.

For this reason, epinephrine is generally administered through routes such as:

• Intramuscular injection
• Intravenous administration
• Intraosseous administration
• Subcutaneous injection in selected circumstances
• Inhalation
• Endotracheal administration in specific resuscitation situations
• Local instillation during airway procedures

Epinephrine and Bronchodilation

Epinephrine was historically used as a bronchodilator because beta-2 stimulation relaxes airway smooth muscle. The medication has been administered by inhalation and injection for bronchospastic conditions, including asthma.

However, epinephrine also stimulates beta-1 receptors in the heart and alpha receptors in blood vessels. This means that bronchodilation may be accompanied by cardiovascular effects such as tachycardia, palpitations, increased blood pressure, and cardiac arrhythmias.

Modern beta-2 agonists such as albuterol and levalbuterol are more selective for receptors in the airway. Therefore, when uncomplicated lower-airway bronchospasm is the primary problem, selective beta-2 agonists are generally preferred.

Epinephrine remains particularly valuable when bronchodilation is only one component of the desired effect, such as during anaphylaxis, when vasoconstriction and cardiovascular stimulation are also needed.

Racemic Epinephrine

Racemic epinephrine is an inhaled form of epinephrine that has an important role in respiratory care. A racemic mixture contains two mirror-image forms, or isomers, of the epinephrine molecule. Only one isomer has substantial adrenergic activity, but the preparation as a whole provides clinically useful alpha and beta effects.

Racemic epinephrine is particularly valuable because of its alpha-mediated vasoconstriction. When delivered to swollen airway tissue, vasoconstriction decreases blood flow to the mucosa and helps reduce edema. This makes racemic epinephrine especially useful in disorders involving upper-airway swelling rather than isolated lower-airway bronchospasm.

A commonly described formulation is a 2.25% solution administered by nebulizer. Protocols vary, but a commonly referenced treatment may involve approximately 0.25 to 0.5 mL of the 2.25% solution diluted with normal saline for nebulization.

Exact dosing and preparation should always be verified according to the specific clinical protocol and medication formulation being used.

Racemic Epinephrine for Upper-Airway Edema

The most important respiratory action of racemic epinephrine is reduction of swollen upper-airway tissue.

Airway edema narrows the internal diameter of the airway. Even relatively small reductions in airway diameter can significantly increase resistance to airflow, particularly in infants and children who already have smaller airways.

When racemic epinephrine stimulates alpha receptors in airway blood vessels, vasoconstriction reduces vascular congestion and tissue swelling. This can rapidly improve airflow through a narrowed upper airway.

Clinical situations in which racemic epinephrine may be considered include:

• Croup
• Postextubation laryngeal edema
• Selected cases of epiglottic or supraglottic swelling
• Inhalation injury
• Airway edema after instrumentation
• Selected airway bleeding situations

Note: Its effects can occur rapidly, often within minutes, but the duration may be relatively short.

Epinephrine for Croup

Croup, also known as laryngotracheobronchitis, is a common pediatric upper-airway disorder usually caused by viral infection. Inflammation and edema develop in the larynx and subglottic airway.

Common manifestations include:

• Barking cough
• Inspiratory stridor
• Hoarseness
• Retractions
• Increased work of breathing
• Respiratory distress

Severe cases may progress to hypoxemia, fatigue, cyanosis, or impending respiratory failure. The benefit of racemic epinephrine in croup is primarily related to alpha-mediated vasoconstriction.

Constriction of blood vessels in the swollen mucosal tissues reduces edema, helping increase the diameter of the upper airway. Improvement may occur within minutes after nebulized administration. However, epinephrine does not treat the underlying inflammatory process.

Corticosteroids such as dexamethasone are commonly used because they provide a more sustained reduction in airway inflammation. Epinephrine provides rapid temporary improvement while the corticosteroid takes effect.

Because the action of nebulized epinephrine can wear off relatively quickly, children with significant croup should continue to be observed after treatment for recurrence of stridor or respiratory distress.

Postextubation Stridor and Laryngeal Edema

Another major respiratory indication for racemic epinephrine is postextubation laryngeal edema. An endotracheal tube can irritate the laryngeal tissues while it remains in place. Trauma during intubation, movement of the tube, prolonged intubation, or pressure from an oversized tube may contribute to inflammation and swelling.

After extubation, airway edema may become clinically apparent. One of the most important signs is inspiratory stridor. Stridor is a harsh, high-pitched sound usually associated with turbulent airflow through a narrowed upper airway.

Other findings may include:

• Hoarseness
• Throat tightness
• Increased inspiratory effort
• Retractions
• Decreased air movement
• Tachypnea
• Hypoxemia

When postextubation laryngeal edema is suspected, nebulized racemic epinephrine may be administered to reduce swelling. One commonly described regimen is 0.5 mL of a 2.25% racemic epinephrine solution diluted with normal saline and delivered by nebulizer.

The patient should be reassessed closely after treatment. Improvement in stridor does not eliminate the possibility that airway obstruction may recur or progress. If upper-airway obstruction becomes severe or ventilation cannot be maintained, endotracheal reintubation may be necessary.

Epinephrine in Epiglottitis

Epiglottitis is a potentially life-threatening condition involving inflammation and swelling of supraglottic structures.

Signs may include:

• Fever
• Severe sore throat
• Drooling
• Difficulty swallowing
• Muffled voice
• Stridor
• Respiratory distress
• Upright or tripod positioning

The primary concern is maintaining a patent airway. Patients with severe epiglottitis may require controlled endotracheal intubation.

Racemic epinephrine may sometimes be available as an adjunct for airway swelling, particularly around the time of extubation when residual inflammation remains a concern.

However, medication should never delay definitive airway management when severe obstruction is present. The patient’s airway status determines the priority of treatment.

Epinephrine During Bronchoscopy

Epinephrine also has a role in controlling localized bleeding during bronchoscopy. Biopsy of an airway lesion may injure blood vessels and cause endobronchial bleeding.

Initial management may include measures such as cold saline instillation. If bleeding continues, local epinephrine may be instilled through the bronchoscope. The desired effect in this situation is alpha-mediated vasoconstriction.

Constriction of blood vessels near the site of injury can:

• Reduce local blood flow
• Decrease bleeding
• Improve visualization during the procedure
• Support hemostasis

Note: This use is different from administering epinephrine as a bronchodilator. The therapeutic target is local vascular constriction.

Epinephrine and Nasotracheal Intubation

Topical adrenergic medications may also be used before nasotracheal intubation. The nasal mucosa contains numerous blood vessels and can bleed when traumatized by an endotracheal tube.

A vasoconstricting medication may be applied to the nares before tube insertion. Racemic epinephrine or another vasoconstrictor such as phenylephrine may be used.

Vasoconstriction can:

• Reduce swelling of the nasal mucosa
• Increase available space in the nasal passage
• Reduce the likelihood of bleeding
• Facilitate passage of the tube

Note: Proper lubrication, tube selection, and airway technique remain essential.

Epinephrine for Anaphylaxis

One of the most important systemic uses of epinephrine is the treatment of anaphylaxis. Anaphylaxis is a severe systemic hypersensitivity reaction that can produce rapid respiratory and cardiovascular deterioration.

Potential manifestations include:

• Airway edema
• Stridor
• Bronchospasm
• Wheezing
• Hypotension
• Vasodilation
• Urticaria
• Gastrointestinal symptoms
• Cardiovascular collapse

Epinephrine is particularly effective because it targets several of these problems simultaneously.

Alpha-1 stimulation causes vasoconstriction, increasing vascular tone and helping support blood pressure. Vasoconstriction also reduces mucosal swelling in the upper airway. Beta-1 stimulation increases heart rate and myocardial contractility. Beta-2 stimulation causes bronchodilation and can help relieve bronchospasm.

This combination makes epinephrine uniquely suited for anaphylaxis. Intramuscular epinephrine is generally the preferred initial route in most cases of anaphylaxis.

Nebulized racemic epinephrine may reduce upper-airway edema but does not replace systemic epinephrine when anaphylaxis causes cardiovascular instability or generalized symptoms.

Epinephrine During Cardiac Arrest

Epinephrine is also an important medication during cardiopulmonary resuscitation. During cardiac arrest, one of the major therapeutic goals is improving blood flow to the heart and brain while high-quality chest compressions continue.

The alpha-adrenergic action of epinephrine produces peripheral vasoconstriction. This increases vascular resistance and can improve coronary perfusion pressure during chest compressions. Epinephrine is used during both shockable and nonshockable cardiac arrest rhythms.

These include:

• Ventricular fibrillation
• Pulseless ventricular tachycardia
• Pulseless electrical activity
• Asystole

A commonly used adult cardiac arrest dose is 1 mg administered intravenously or intraosseously every 3 to 5 minutes during resuscitation.

High-quality cardiopulmonary resuscitation should continue with minimal interruption while medications are administered. Routine use of excessively high doses of epinephrine is not recommended.

Epinephrine and Bradycardia

Because beta-1 stimulation increases heart rate and cardiac contractility, epinephrine may also be used in selected cases of clinically significant bradycardia.

Symptomatic bradycardia may present with:

• Hypotension
• Altered mental status
• Chest discomfort
• Signs of shock
• Acute heart failure

Treatment depends on the underlying cause and severity. Medications that increase heart rate may include atropine, epinephrine, or dopamine.

Epinephrine may be administered by infusion in selected patients when other interventions are inadequate or inappropriate.

Continuous cardiac and blood pressure monitoring is important because excessive adrenergic stimulation can cause tachycardia, hypertension, or arrhythmias.

Epinephrine in Neonatal Resuscitation

Epinephrine may be required during neonatal resuscitation when severe bradycardia persists despite adequate respiratory and circulatory support. Effective ventilation is the most important intervention for most newborns requiring resuscitation.

If the heart rate remains below 60 beats/min despite effective positive-pressure ventilation, chest compressions are initiated. If the heart rate continues below 60 beats/min despite effective ventilation and coordinated chest compressions, epinephrine may be indicated.

This sequence is important. Epinephrine should not be used as a substitute for effective ventilation. The preferred route is vascular administration, commonly through umbilical venous access during neonatal resuscitation.

Endotracheal administration may be considered when vascular access has not yet been established, although drug absorption through the endotracheal route is less predictable. Correct concentration and dose are particularly important in newborns because dosing errors can cause severe cardiovascular complications.

Effects on Pulmonary Vascular Resistance

Epinephrine can influence the pulmonary circulation through its adrenergic effects. Alpha-mediated vasoconstriction may increase pulmonary vascular resistance in some circumstances.

Pulmonary vascular resistance represents the resistance that the right ventricle must overcome to eject blood through the pulmonary circulation. When pulmonary vascular resistance rises, right ventricular afterload increases.

The overall hemodynamic effect of epinephrine depends on dose, receptor distribution, patient condition, and underlying cardiopulmonary physiology. This is one reason epinephrine should be considered a broad cardiovascular medication rather than merely a bronchodilator.

Effects on Systemic Vascular Resistance

Alpha-1 stimulation can also increase systemic vascular resistance. Systemic vascular resistance represents the resistance against which the left ventricle ejects blood.

Vasoconstriction narrows systemic blood vessels, which can raise arterial blood pressure.

This effect is beneficial during severe vasodilation or circulatory collapse but can increase ventricular workload and myocardial oxygen demand. The hemodynamic response must therefore be considered in patients with significant cardiovascular disease.

Adverse Effects of Epinephrine

The same receptor activity responsible for epinephrine’s therapeutic effects can produce adverse reactions.

Common adverse effects include:

• Tachycardia
• Palpitations
• Hypertension
• Cardiac arrhythmias
• Tremor
• Nervousness
• Anxiety
• Headache
• Dizziness
• Nausea
• Insomnia

Beta-1 stimulation contributes to increased heart rate and myocardial contractility. Alpha stimulation may increase blood pressure. Beta stimulation of skeletal muscle can contribute to tremor.

The likelihood and severity of these effects depend on dose, route, frequency of administration, underlying cardiovascular disease, and other medications being used. Repeated doses or systemic administration generally produce greater cardiovascular effects than localized aerosol therapy.

Monitoring During Epinephrine Therapy

Patient monitoring depends on the route and indication.

Important parameters may include:

• Heart rate
• Cardiac rhythm
• Blood pressure
• Respiratory rate
• Breath sounds
• Work of breathing
• Oxygen saturation
• Airway patency
• Level of consciousness

When racemic epinephrine is given for upper-airway obstruction, improvement should be assessed by examining stridor, retractions, air movement, respiratory effort, and oxygenation.

During systemic administration, cardiovascular monitoring becomes particularly important. A significant increase in heart rate, development of an arrhythmia, or severe hypertension should prompt immediate reassessment.

Epinephrine Concentrations

Epinephrine is available in several concentrations, and confusion between formulations can lead to serious medication errors. Historically, concentrations have often been expressed as ratios.

A 1:1000 solution contains:

1 mg/mL

A 1:10,000 solution contains:

0.1 mg/mL

Racemic epinephrine intended for inhalation may be supplied as a 2.25% solution.

Because these concentrations differ substantially, the concentration and intended route must always be verified before administration.

Medication errors involving epinephrine can produce severe hypertension, arrhythmias, myocardial injury, or other life-threatening complications.

Stability and Storage

Epinephrine is chemically sensitive to environmental exposure. Light, heat, and air can contribute to oxidation. As oxidation progresses, epinephrine solutions may become pink, reddish, or brown.

A discolored solution may indicate degradation and should not be used when the product instructions identify discoloration as evidence of instability.

Commercial products are therefore often packaged to reduce exposure to light. Careful inspection of the medication before administration helps reduce the risk of using a degraded preparation.

Epinephrine Compared With Selective Beta-2 Agonists

Epinephrine and medications such as albuterol can both produce bronchodilation, but they are not interchangeable in terms of receptor selectivity.

Epinephrine stimulates:

• Alpha receptors
• Beta-1 receptors
• Beta-2 receptors

Albuterol primarily targets beta-2 receptors. This difference explains why albuterol is usually preferred when isolated bronchospasm is the main therapeutic target.

Selective beta-2 activity provides bronchodilation with less direct cardiac stimulation than a nonselective medication such as epinephrine. However, albuterol does not provide the same strong alpha-mediated vasoconstriction.

For upper-airway edema, anaphylaxis, or situations requiring both vascular and respiratory effects, epinephrine may be more appropriate. The appropriate drug depends on the physiologic problem being treated.

Key Clinical Distinctions

Several clinical distinctions help determine when epinephrine is appropriate.

• Wheezing generally suggests lower-airway narrowing caused by bronchospasm, secretions, or airway inflammation.
• Stridor generally suggests upper-airway obstruction.
• A patient with isolated wheezing from bronchospasm may benefit primarily from a selective beta-2 agonist.
• A patient with inspiratory stridor caused by upper-airway edema may benefit from nebulized racemic epinephrine.
• A patient with anaphylaxis involving hypotension, bronchospasm, and airway swelling requires systemic epinephrine because treatment must address both respiratory and cardiovascular abnormalities.
• A patient experiencing cardiac arrest may receive intravenous or intraosseous epinephrine to increase vascular tone and improve perfusion during resuscitation.

Note: The medication may be the same, but the intended therapeutic effect differs according to the clinical situation.

Epinephrine Practice Questions

1. What type of medication is epinephrine?
Epinephrine is a nonselective adrenergic agonist and naturally occurring catecholamine that stimulates alpha- and beta-adrenergic receptors.

2. What is another name for epinephrine?
Epinephrine is also known as adrenaline.

3. Which major adrenergic receptors are stimulated by epinephrine?
Epinephrine primarily stimulates alpha-1, beta-1, and beta-2 adrenergic receptors.

4. What is the primary effect of alpha-1 receptor stimulation by epinephrine?
Alpha-1 receptor stimulation causes vasoconstriction, which can increase vascular resistance and reduce mucosal swelling.

5. What cardiovascular effects result from beta-1 receptor stimulation by epinephrine?
Beta-1 receptor stimulation increases heart rate, myocardial contractility, cardiac conduction, and cardiac excitability.

6. What respiratory effect results from beta-2 receptor stimulation by epinephrine?
Beta-2 receptor stimulation relaxes bronchial smooth muscle, resulting in bronchodilation.

7. How does beta-2 receptor stimulation produce bronchial smooth-muscle relaxation?
Beta-2 receptor activation stimulates a G protein-linked pathway that activates adenylyl cyclase, increases intracellular cAMP, and promotes smooth-muscle relaxation.

8. Why is epinephrine generally not preferred over albuterol for routine treatment of bronchospasm?
Epinephrine is nonselective and stimulates beta-1 and alpha receptors in addition to beta-2 receptors, resulting in more cardiovascular effects than selective beta-2 agonists such as albuterol.

9. What is the primary respiratory benefit of racemic epinephrine in upper-airway edema?
Racemic epinephrine produces alpha-mediated vasoconstriction of airway blood vessels, which decreases mucosal swelling and increases airway caliber.

10. Which respiratory sound commonly suggests an indication for racemic epinephrine after extubation?
Inspiratory stridor suggests upper-airway narrowing from laryngeal edema and may indicate a need for nebulized racemic epinephrine.

11. What concentration of racemic epinephrine is commonly used for nebulized treatment?
Racemic epinephrine is commonly supplied as a 2.25% solution for nebulization.

12. What commonly referenced dose of racemic epinephrine may be used for postextubation stridor?
A commonly referenced regimen is 0.5 mL of 2.25% racemic epinephrine diluted with normal saline and administered by nebulizer.

13. Why is racemic epinephrine useful in the treatment of croup?
It constricts blood vessels in swollen upper-airway mucosa, reducing subglottic edema and improving airflow.

14. What are three common clinical findings associated with croup?
Common findings include a barking cough, inspiratory stridor, and increased work of breathing or retractions.

15. Why should a child continue to be observed after receiving nebulized racemic epinephrine for croup?
The effects of racemic epinephrine are relatively short-lived, so airway swelling and respiratory symptoms may recur as the medication wears off.

16. What medication is commonly used with epinephrine to provide a more sustained reduction in airway inflammation in croup?
A corticosteroid such as dexamethasone is commonly administered to provide a longer-lasting anti-inflammatory effect.

17. What should be considered if severe postextubation airway obstruction does not improve with racemic epinephrine?
Reintubation may be necessary if adequate ventilation and airway patency cannot be maintained.

18. How can epinephrine help control bleeding during bronchoscopy?
Local epinephrine causes alpha-mediated vasoconstriction, decreasing blood flow from injured airway vessels and helping achieve hemostasis.

19. Why might an adrenergic vasoconstrictor be applied before nasotracheal intubation?
Vasoconstriction reduces nasal mucosal swelling and bleeding, which can make passage of the endotracheal tube easier.

20. Why is epinephrine particularly useful during anaphylaxis?
Epinephrine simultaneously produces vasoconstriction, supports cardiac activity, reduces airway edema, and causes bronchodilation through its alpha-1, beta-1, and beta-2 effects.

21. What is generally the preferred initial route for epinephrine administration during anaphylaxis?
Intramuscular administration is generally the preferred initial route for treating anaphylaxis.

22. Why does nebulized racemic epinephrine not replace systemic epinephrine during anaphylaxis?
Nebulized racemic epinephrine may decrease upper-airway edema, but it does not adequately treat the systemic vasodilation, hypotension, and cardiovascular instability associated with anaphylaxis.

23. What is the commonly used adult epinephrine dose during cardiac arrest?
The commonly used adult dose is 1 mg administered intravenously or intraosseously every 3 to 5 minutes during cardiac arrest.

24. What is the primary benefit of alpha-adrenergic stimulation from epinephrine during cardiac arrest?
Alpha-mediated peripheral vasoconstriction increases vascular resistance and can improve coronary perfusion pressure during chest compressions.

25. When should epinephrine be considered during neonatal resuscitation?
Epinephrine should be considered when the newborn’s heart rate remains below 60 beats/min despite effective positive-pressure ventilation and coordinated chest compressions.

26. Why does epinephrine have a relatively short duration of action?
Epinephrine is rapidly metabolized by enzymes such as catechol O-methyltransferase and monoamine oxidase.

27. Why is epinephrine generally ineffective when administered orally?
It is rapidly metabolized in the gastrointestinal tract and liver, which greatly reduces its bioavailability.

28. What does increased cAMP do in bronchial smooth muscle?
Increased cAMP promotes smooth-muscle relaxation, helping produce bronchodilation.

29. How can epinephrine affect systemic vascular resistance?
Alpha-1 receptor stimulation causes systemic vasoconstriction, which can increase systemic vascular resistance.

30. How can epinephrine affect pulmonary vascular resistance?
Its alpha-mediated vasoconstricting effects can increase pulmonary vascular resistance in some clinical situations.

31. What effect can epinephrine have on myocardial oxygen demand?
Epinephrine can increase myocardial oxygen demand because it increases heart rate and contractility.

32. Why can epinephrine increase the risk of cardiac arrhythmias?
Beta-1 stimulation increases cardiac excitability and conduction, which can contribute to dysrhythmias.

33. What are common cardiovascular adverse effects of epinephrine?
Common cardiovascular adverse effects include tachycardia, palpitations, hypertension, and cardiac arrhythmias.

34. What neurologic or systemic adverse effects may occur with epinephrine?
Possible effects include nervousness, tremor, headache, dizziness, and insomnia.

35. What respiratory finding helps distinguish upper-airway obstruction from lower-airway bronchospasm?
Inspiratory stridor generally points toward upper-airway obstruction, whereas wheezing is more commonly associated with lower-airway narrowing.

36. What is the primary purpose of racemic epinephrine in postextubation laryngeal edema?
Its primary purpose is to reduce mucosal swelling through local vasoconstriction.

37. Why can airway edema become especially dangerous in infants and young children?
Their smaller airway diameter means that a relatively small amount of swelling can cause a large increase in airflow resistance.

38. What should be monitored after administering racemic epinephrine for upper-airway obstruction?
The patient should be monitored for stridor, retractions, air movement, respiratory effort, oxygenation, heart rate, and overall airway patency.

39. Why does improvement after racemic epinephrine not eliminate the need for continued airway observation?
The medication’s effect is temporary, and airway edema may recur as the vasoconstricting effect wears off.

40. What is the main therapeutic role of epinephrine during localized airway bleeding?
It produces vasoconstriction at the bleeding site, reducing blood flow and supporting hemostasis.

41. What is a major safety concern when using different epinephrine preparations?
Different concentrations and formulations can be confused, creating a risk of serious dosing errors.

42. How much epinephrine is contained in a 1:1000 solution?
A 1:1000 epinephrine solution contains 1 mg/mL.

43. How much epinephrine is contained in a 1:10,000 solution?
A 1:10,000 epinephrine solution contains 0.1 mg/mL.

44. Why should epinephrine solutions be protected from excessive light and air exposure?
Exposure can promote oxidation and chemical degradation of the medication.

45. What may discoloration of an epinephrine solution indicate?
Pink, reddish, or brown discoloration may indicate oxidation and degradation of the medication.

46. What is the relationship between epinephrine and the sympathetic nervous system?
Epinephrine mimics and amplifies sympathetic nervous system activity by stimulating adrenergic receptors.

47. How does epinephrine affect cardiac output?
By increasing heart rate and myocardial contractility, epinephrine can increase cardiac output.

48. Why may epinephrine be used in severe symptomatic bradycardia?
Its beta-1 effects can increase heart rate and myocardial contractility when clinically significant bradycardia persists.

49. What route is commonly preferred for epinephrine during neonatal resuscitation when vascular access is available?
Umbilical venous or another appropriate vascular route is preferred because absorption is more reliable than with endotracheal administration.

50. Why is endotracheal epinephrine less desirable than vascular administration during resuscitation?
Absorption through the endotracheal route is less predictable, making drug delivery and effect less reliable.

51. What is the primary difference between epinephrine and a selective beta-2 agonist?
Epinephrine stimulates alpha-1, beta-1, and beta-2 receptors, while a selective beta-2 agonist primarily targets beta-2 receptors in the airways.

52. Why can epinephrine raise arterial blood pressure?
Its alpha-1 effects cause peripheral vasoconstriction, which increases vascular resistance and can elevate blood pressure.

53. How does epinephrine reduce mucosal edema?
It constricts blood vessels supplying swollen mucosal tissue, reducing vascular engorgement and tissue swelling.

54. Why can epinephrine be useful in both airway and cardiovascular emergencies?
Its broad receptor activity allows it to affect airway smooth muscle, vascular tone, heart rate, and cardiac contractility at the same time.

55. What effect does beta-1 stimulation have on myocardial contractility?
Beta-1 stimulation increases the force of cardiac contraction.

56. What effect does beta-1 stimulation have on cardiac conduction?
Beta-1 stimulation increases conduction through the cardiac electrical system.

57. What effect does beta-2 stimulation have on airway resistance?
Beta-2 stimulation decreases airway resistance by relaxing bronchial smooth muscle and increasing airway diameter.

58. Why is racemic epinephrine considered more useful for airway edema than for routine asthma treatment?
Its alpha-mediated vasoconstriction is particularly helpful for swollen upper-airway tissues, while more selective beta-2 agonists are generally preferred for routine bronchospasm.

59. What type of airway problem is suggested by a barking cough and inspiratory stridor?
These findings suggest an upper-airway disorder such as croup involving subglottic narrowing.

60. What is the major airway abnormality in croup that racemic epinephrine helps treat?
Racemic epinephrine helps reduce subglottic mucosal edema.

61. Why should severe stridor never be treated with medication alone if ventilation is deteriorating?
Severe upper-airway obstruction may require immediate airway stabilization or intubation because medication may not act quickly or effectively enough to maintain ventilation.

62. What is the primary concern in a patient with epiglottitis who develops worsening stridor?
The primary concern is progressive upper-airway obstruction that may require establishment of a secure airway.

63. What should be available when a patient at risk for severe postextubation edema is extubated?
Appropriate oxygen, suction, nebulized racemic epinephrine, and equipment for emergency reintubation should be readily available.

64. What physiologic effect of epinephrine is used when it is instilled onto a bleeding bronchoscopic biopsy site?
Its alpha-adrenergic vasoconstricting effect is used to reduce local blood flow.

65. Why may cold saline be used before epinephrine during bronchoscopy-related bleeding?
Cold saline may help decrease bleeding initially, while local epinephrine may be considered if bleeding continues.

66. What major physiologic problems can occur simultaneously during anaphylaxis?
Anaphylaxis can cause vasodilation, hypotension, bronchospasm, and upper-airway edema.

67. How does alpha-1 stimulation help correct hypotension during anaphylaxis?
Alpha-1 stimulation constricts blood vessels, increasing vascular tone and systemic vascular resistance.

68. How does beta-2 stimulation help during anaphylaxis?
Beta-2 stimulation relaxes bronchial smooth muscle, helping relieve bronchospasm.

69. How does beta-1 stimulation help support circulation during anaphylaxis?
Beta-1 stimulation increases heart rate and myocardial contractility, which can support cardiac output.

70. Why can systemic epinephrine produce more adverse effects than inhaled racemic epinephrine?
Systemic administration exposes adrenergic receptors throughout the body to the medication, increasing cardiovascular and other systemic effects.

71. What is one reason frequent racemic epinephrine treatments require close cardiovascular monitoring?
Repeated adrenergic stimulation can produce tachycardia, hypertension, palpitations, and other cardiovascular effects.

72. What is the significance of epinephrine increasing cardiac excitability?
Increased cardiac excitability can make the myocardium more susceptible to abnormal rhythms.

73. Why can increased systemic vascular resistance raise left ventricular workload?
The left ventricle must pump against greater resistance when systemic blood vessels are constricted.

74. Why can increased pulmonary vascular resistance raise right ventricular workload?
The right ventricle must generate more pressure to move blood through a more resistant pulmonary circulation.

75. What is the most important general safety principle when preparing epinephrine?
The clinician should verify the exact formulation, concentration, dose, and intended route before administration because epinephrine is available in multiple preparations.

76. Why is epinephrine considered a nonselective adrenergic agonist?
It stimulates multiple adrenergic receptor types, including alpha-1, beta-1, and beta-2 receptors.

77. What is the main purpose of using racemic epinephrine after extubation?
The main purpose is to reduce laryngeal swelling and improve airflow when postextubation edema causes stridor.

78. What type of breath sound is more consistent with lower-airway bronchospasm than upper-airway edema?
Wheezing is more consistent with lower-airway bronchospasm.

79. Why can epinephrine improve airway caliber in two different ways?
It can relax bronchial smooth muscle through beta-2 stimulation and reduce mucosal swelling through alpha-mediated vasoconstriction.

80. What enzyme activates the intracellular pathway responsible for increased cAMP after beta-receptor stimulation?
Adenylyl cyclase is activated, leading to increased intracellular cAMP.

81. How does increased cAMP contribute to bronchodilation?
It reduces smooth-muscle contraction by decreasing calcium-dependent contractile activity and promoting relaxation.

82. What effect does epinephrine have on vascular smooth muscle through alpha receptors?
It causes contraction of vascular smooth muscle and produces vasoconstriction.

83. Why is racemic epinephrine sometimes referred to as a topical vasoconstrictor in respiratory care?
When inhaled, it acts locally on airway blood vessels to reduce mucosal congestion and edema.

84. What is one reason prolonged intubation can increase the risk of postextubation stridor?
Prolonged pressure and irritation from the endotracheal tube can cause laryngeal inflammation and edema.

85. What finding after extubation should prompt immediate assessment for upper-airway narrowing?
New inspiratory stridor should prompt immediate assessment for laryngeal or upper-airway edema.

86. Why can postextubation edema worsen after removal of the endotracheal tube?
Swollen laryngeal tissue can become more apparent once the tube is removed and no longer physically maintains an airway opening.

87. What is the role of epinephrine in severe inhalation injury with airway swelling?
Aerosolized racemic epinephrine may reduce airway edema through vasoconstriction and may also provide some bronchodilation.

88. Why is epinephrine not considered a maintenance bronchodilator?
Its duration of action is relatively short and its nonselective receptor activity causes more systemic adverse effects than longer-acting, more selective agents.

89. What historic role did epinephrine have in aerosol therapy?
Epinephrine was one of the earliest medications used as an inhaled aerosol for treatment of respiratory disease.

90. What happens to airway blood flow when alpha-1 receptors are stimulated by epinephrine?
Airway blood vessels constrict, reducing blood flow to swollen mucosal tissues.

91. What effect can epinephrine have on stroke volume?
Beta-1 stimulation can increase myocardial contractility and may increase stroke volume.

92. Why should heart rate be monitored during aerosolized adrenergic therapy?
Adrenergic stimulation can increase heart rate, and excessive tachycardia may indicate a significant adverse response.

93. Why may patients with underlying cardiac disease require particular caution when receiving epinephrine?
The medication can increase heart rate, contractility, blood pressure, myocardial oxygen demand, and the risk of arrhythmias.

94. What is the significance of a temporary response to racemic epinephrine in upper-airway obstruction?
A temporary improvement does not mean the underlying condition has resolved, so continued monitoring and treatment of the cause remain necessary.

95. What does positive chronotropic activity mean in relation to epinephrine?
It means epinephrine can increase heart rate.

96. What does positive inotropic activity mean in relation to epinephrine?
It means epinephrine can increase the force of myocardial contraction.

97. Why can alpha-mediated vasoconstriction be useful during severe hypotension?
Vasoconstriction increases vascular tone and systemic vascular resistance, which can help raise arterial blood pressure.

98. Why is medication concentration especially important when calculating an epinephrine dose?
Different epinephrine formulations contain substantially different amounts of drug per milliliter, so confusing concentrations can cause a major dosing error.

99. What should happen to cardiopulmonary resuscitation while epinephrine is being administered during cardiac arrest?
High-quality chest compressions should continue with minimal interruption while the medication is administered.

100. What overall feature explains the wide range of clinical uses of epinephrine?
Its ability to stimulate alpha-1, beta-1, and beta-2 receptors allows it to affect vascular tone, cardiac activity, airway smooth muscle, and mucosal swelling.

Final Thoughts

Epinephrine is a powerful nonselective adrenergic agonist that affects the airways, heart, and circulation through alpha-1, beta-1, and beta-2 receptor stimulation. Its alpha effects produce vasoconstriction and reduce mucosal swelling, its beta-1 effects increase cardiac activity, and its beta-2 effects produce bronchodilation.

These actions explain its use in anaphylaxis, cardiac arrest, severe bradycardia, croup, postextubation stridor, airway bleeding, and selected respiratory emergencies.

Because epinephrine can also cause tachycardia, hypertension, arrhythmias, and other systemic effects, correct dosing, concentration, route selection, and careful patient monitoring are essential.