Dopamine is preferred in the management of shock, because it?

RUHS, Jaipur, M.Sc Nursing Entrance Exam-2018

Pharmacology

Hard

Appeared in: RUHS, Jaipur, M.Sc Nursing Entrance Exam-2018

Explanation

At low doses (typically 1-3 mcg/kg/min), dopamine selectively stimulates dopaminergic (D1) receptors located in the renal and mesenteric vascular beds.
This D1 receptor stimulation leads to vasodilation (widening of blood vessels) specifically in the kidneys.
The resulting increase in renal blood flow is thought to improve urine output and help preserve kidney function during states of shock, which is a unique property among vasopressors.

Option A: This is the opposite of dopamine's effect on the heart. At moderate doses (3-10 mcg/kg/min), dopamine stimulates beta-1 adrenergic receptors, which increases myocardial contractility and heart rate, thereby increasing cardiac output.
Option B: Dopamine has a very short elimination half-life of less than 2 minutes. This means its effects cease quickly after the infusion is stopped, requiring continuous intravenous administration to maintain its therapeutic effect.
Option C: While dopamine does cause peripheral vasoconstriction, this effect only occurs at high doses (greater than 10 mcg/kg/min) due to alpha-1 receptor stimulation. This is not the unique reason for its preference, as other drugs like norepinephrine are more potent vasoconstrictors.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Pharmacology of Dopamine in Shock Management as background academic context rather than a clinical decision trigger.
Nurses administering dopamine must perform meticulous titration of the infusion rate based on the desired hemodynamic effect (e.g., improved urine output vs. increased blood pressure) and continuously monitor vital signs.
The short half-life of dopamine means that any change in the infusion rate will have a rapid effect, but also that accidental discontinuation or infiltration can lead to sudden and severe hypotension.
What if the patient's shock is due to sepsis and they remain hypotensive despite a high dose of dopamine? According to current guidelines, the nurse should anticipate an order to add or switch to norepinephrine, which is the first-line vasopressor for septic shock due to its potent vasoconstrictive effects and lower risk of tachyarrhythmias compared to dopamine.

How to Approach the Question

First, identify the core of the question. It asks for the specific, distinguishing reason dopamine is used in shock.
Recall the pharmacology of dopamine, focusing on the fact that its effects are highly dose-dependent and it acts on multiple receptor types.
Systematically evaluate each option. Ask yourself: 'Is this statement true about dopamine? And if so, is it the unique reason for its use in shock?'
Eliminate options that are factually incorrect. Dopamine increases, not decreases, cardiac output, and it has a very short, not prolonged, action.
Compare the remaining options. Dopamine does cause vasoconstriction at high doses, but its renal vasodilatory effect at low doses is a unique characteristic often highlighted in pharmacology.
Select the option that describes this unique mechanism, as this is a common point of testing for this drug.

Concept Tested & Keywords

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E6 Pharmacology Nursing Lilley 11e Part 1 p. 318-320

E6 Medicine Harrison 22e Part 2 p. 219-221