Prehospital Academy Lesson 12.5
Paramedic Medications: Sympathetic Nervous System
Introduction
This lecture focuses on medications that impact the sympathetic nervous system, also known as the "fight or flight" system. A deep understanding of these drugs is critical for paramedics to effectively manage a variety of emergency medical conditions. Remember to always follow your local protocols and consult with medical control as needed.
The Sympathetic Nervous System and its Receptors
The sympathetic nervous system utilizes several key receptors to exert its effects. For our purposes in EMS, we are primarily concerned with the following:
Alpha-1 Receptors: Primarily cause vasoconstriction when stimulated, leading to an increase in blood pressure.
Beta-1 Receptors: Located mainly in the heart, stimulation of these receptors increases heart rate, contractility, and cardiac output.
Beta-2 Receptors: Found predominantly in the lungs, stimulation of beta-2 receptors leads to bronchodilation.
Dopaminergic Receptors: These are found in the renal, mesenteric, and cerebral arteries. Stimulation can lead to vasodilation.
Sympathomimetic Drugs (Adrenergics)
Sympathomimetics are drugs that mimic the effects of the sympathetic nervous system by stimulating its receptors. Common sympathomimetics used in the prehospital setting include:
Epinephrine: A potent stimulator of alpha-1, beta-1, and beta-2 receptors. It is used in cardiac arrest, anaphylaxis, and severe asthma to increase heart rate and contractility, constrict blood vessels, and open the airways.
Norepinephrine (Levophed): Primarily stimulates alpha-1 receptors, causing potent vasoconstriction. It is used to treat severe hypotension, particularly in cardiogenic and septic shock.
Dopamine: Has dose-dependent effects. At low doses, it stimulates dopaminergic receptors, causing vasodilation in the kidneys. At moderate doses, it stimulates beta-1 receptors, increasing cardiac output. At high doses, it stimulates alpha-1 receptors, causing vasoconstriction.
Albuterol: A selective beta-2 agonist, albuterol is used to treat bronchospasm in asthma and COPD by causing bronchodilation.
Dobutamine: Primarily a beta-1 agonist, dobutamine increases cardiac contractility and is used in the management of heart failure.
Sympatholytic Drugs (Adrenergic Blockers)
Sympatholytics, or adrenergic blockers, inhibit the sympathetic nervous system by blocking its receptors. These are commonly referred to as "beta-blockers."
Beta-Blockers (e.g., Metoprolol, Labetalol): These medications block beta-receptors, leading to a decrease in heart rate, blood pressure, and cardiac contractility. They are often used to treat hypertension, angina, and certain cardiac dysrhythmias.
Critical Thinking Questions
Explain why epinephrine is the drug of choice for treating anaphylaxis, referencing its effects on the different adrenergic receptors.
A patient is in cardiogenic shock with severe hypotension. Would you expect to administer a sympathomimetic or a sympatholytic? Explain your reasoning.
Describe the dose-dependent effects of dopamine and how a paramedic might titrate this medication based on the patient's presentation.
Why is albuterol effective in treating an asthma attack? What are some potential side effects a paramedic should monitor for?
What are the primary therapeutic goals when administering a beta-blocker in the prehospital setting?