Sympathomimetic or Adrenergic Agents

Actions: Mimics the effects of the sympathetic nervous system this group of agents stimulates the heart rate to increase, has a positive inotropic effect on the heart muscle, relaxes the smooth muscle of the lungs (bronchio-dilation), relaxation of gastrointestinal track smooth muscle and inhibition or constriction of gastric sphincters, and vasoconstriction of peripheral blood vessels epically of the skin.

Stimulated by a broad class of drugs: catecholamines and noncatecholamines. Naturally occuring catecholamines in the body are Norepinephrine, Epinephrine (Adrenalin)* and Dopamine. All three of these agents are synthetically produced and may be administered as pharmacological agents. Non-catecholamine adrenergic agents are Ephedrine, Phenylephrine (Neo-synephrine)* and Terbutaline.

The autonomic nervous system can be sub-divided by its three primary receptor sites: alpha, beta and dopaminergic.

In short:

• alpha-1 receptors are found in the peripheral vascular system and when stimulated by cause vasoconstriction.
• beta-1 receptors are found in the heart and when stimulated cause increase in the heart rate and force of contractility.
• beta-2 receptors are found in both the heart and lungs and when stimulated cause relaxation of the smooth muscles of the bronchi (bronco dilation) and relaxation of peripheral blood vessels (vasodilation).
• dopaminergic receptors are found in the mesentery arteries, lower gastrointestinal and renal arteries and when stimulated improve symptoms associated with Parkinson's disease and increase perfusion to the gut and kidneys (increasing renal output).

See chapter 18, chart on page 146 figure 18-2 for description of "Receptor Specificity of Representative Adrenergic Agonist."

Uses: Clinical uses of adrenergic agents are the treatment of shock states, such as hypotension, and acute renal failure.

Premedication Assessment:

1. Take baseline vital signs of heart rate and blood pressure.
2. Assess baseline respiratory function and status.
3. Assess baseline neurological status.
4. Assure patency of intravenous site and document. Obtain Infusion pump as soon as possible.

Planning:
When administering catecholamines the dosage is often titrated based on patients weigh in kg and specific dose effect desried of medication. Dosages may be titrated for a specific heart rate, blood pressure or specific urine output.

Administer medications intravenously preferably via central line and infusion pump. In emergency short-term situations a microdrip set may be hand regulated.

Implementation:
A common formula utilized to calculate dosage is micrograms per kilogram per minute when taking weight of patient in to account (Dopamine). However some medications such as Neo-synephrine may be calculate using micrograms per minute not taking weight into account. Always consult drug guides and nursing unit protocols when administering adrenergic agents.

Many adrenergic agents are optimally infused via a central line as extravasations at injection may cause tissue necrosis. Tissue infiltration of Dopamine may cause a "Dopamine Burn" which can be treated with subcutaneous phentolamine (Regitine).

Evaluation:
Associated side effects of adrenergic agents are usually dose related and resolve with either decreasing dosage or discontinuing the therapy.

Beware of patients with known dysfunctions of the major systems who are may be more sensitive to side effects (e.g., hypertension, heart disease, impaired hepatic function, thyroid disease and /or diabetes.Document dosage, desired effects, and concentration of fluids and patency of intravenous site.

Side effects to Expect:
Palpitations, mild tachycardia, skin flushing, dizziness, tremors.

Side-effects to Report:
Dysrhythmias, chest pain, severe hypotension, hypertension, Infiltration of medication, nausea and vomiting.

Drug Interactions:
Monoamine oxidase inhibitors (MOI), tricyclic antidepressants, atropine, guanethidine, or halothane anesthesia.