Which of the following drugs increases afterload? Select all that apply.
Levophed (Norepinephrine) at 4 mcg/min.
Dopamine at 20 mcg/kg/min.
Nitroglycerin at 5 mcg.
Metoprolol 5 mg IV.
Dopamine at 5 mcg/kg/min.
Correct Answer : A,B
Choice A rationale
Norepinephrine is a potent alpha-1 adrenergic agonist that causes significant peripheral vasoconstriction. By increasing the systemic vascular resistance, the heart must work harder to eject blood into the aorta. This increase in the resistance against which the left ventricle must pump is the definition of afterload. At a dose of 4 mcg/min, the alpha-adrenergic effects are prominent, directly raising the arterial pressure and increasing the workload and oxygen demand of the myocardial tissue.
Choice B rationale
Dopamine at high doses (10 to 20 mcg/kg/min) primarily stimulates alpha-1 adrenergic receptors in the systemic vasculature. This stimulation results in profound vasoconstriction and an increase in systemic vascular resistance. Consequently, the afterload is significantly elevated. While it also has beta-1 effects that increase contractility, the dominant vascular effect at this high dosage range is the constriction of arterioles, which requires the heart to overcome greater resistance during the systolic phase of the cardiac cycle.
Choice C rationale
Nitroglycerin is a potent vasodilator that primarily acts on the venous system at low doses and the arterial system at higher doses. By relaxing the smooth muscle in blood vessels, it decreases systemic vascular resistance and venous return. This action results in a decrease in afterload and preload, rather than an increase. It is frequently used in clinical practice to reduce the workload of the heart and improve myocardial oxygen balance in conditions like heart failure or angina.
Choice D rationale
Metoprolol is a cardioselective beta-1 adrenergic antagonist that reduces heart rate, contractility, and cardiac output. While it blocks the compensatory tachycardia associated with some forms of heart failure, it does not typically increase afterload. In fact, by reducing the overall sympathetic drive and potentially lowering blood pressure over time, it may lead to a decrease or stabilization of afterload. It does not possess the alpha-adrenergic stimulating properties required to cause systemic vasoconstriction and increase resistance.
Choice E rationale
At a moderate dose of 5 mcg/kg/min, dopamine primarily targets beta-1 adrenergic receptors, which increases myocardial contractility and heart rate. While there is some dopaminergic stimulation that improves renal blood flow, the alpha-adrenergic effects that cause vasoconstriction and increased afterload are usually not dominant at this level. This dosage is often referred to as the cardiac dose, focusing on improving cardiac output through inotropy rather than significantly altering the systemic vascular resistance or afterload.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is C
Explanation
Choice A rationale
Endotracheal intubation is indicated for respiratory failure or an inability to protect the airway. This patient is currently breathing spontaneously with an oxygen saturation of 95 percent, which is within the normal range of 95 to 100 percent. Intubation is an invasive procedure with risks such as ventilator associated pneumonia. It is not the priority intervention when clinical signs suggest an immediate mechanical issue like a tension pneumothorax or hemothorax resulting from the rib fractures.
Choice B rationale
Lactated Ringer's solution is used for fluid resuscitation in hypovolemic shock. While rib fractures can cause internal bleeding, giving a liter wide open without assessing the cause of respiratory distress can worsen outcomes, especially if the patient has a pulmonary contusion. The priority is addressing the mechanical compromise of the chest wall and pleural space. Excessive fluid can lead to pulmonary edema, further decreasing the efficiency of gas exchange in a patient with thoracic trauma.
Choice C rationale
Rib fractures from blunt chest trauma significantly increase the risk of a tension pneumothorax or hemothorax. A tension pneumothorax is a life threatening emergency where air enters the pleural space but cannot exit, increasing intrathoracic pressure. This shifts mediastinal structures and compresses the heart and great vessels, leading to obstructive shock. Needle thoracostomy provides immediate decompression of the pleural space, followed by chest tube insertion to restore negative pressure and allow for lung re-expansion.
Choice D rationale
A chest x-ray is a valuable diagnostic tool to identify the extent of rib fractures, presence of a pneumothorax, or pulmonary contusions. However, in the setting of acute thoracic trauma and potential respiratory compromise, waiting for imaging can delay life saving treatment. If a tension pneumothorax is suspected clinically based on symptoms and mechanism of injury, immediate decompression is required before radiographic confirmation. Assessment and intervention for airway, breathing, and circulation must always precede diagnostic imaging studies.
Correct Answer is C
Explanation
Choice A rationale
Magnesium sulfate administration is scientifically indicated because the patient's magnesium level is 0.2 mEq/L, which is significantly lower than the normal range of 1.5 to 2.5 mEq/L. Hypomagnesemia increases myocardial irritability and can directly precipitate premature ventricular contractions or torsades de pointes. Providing 2 grams intravenously helps stabilize the cardiac membrane potential by restoring the necessary cofactor for the sodium potassium adenosine triphosphatase pump, which maintains the appropriate intracellular and extracellular electrolyte gradients.
Choice B rationale
Increasing oxygen to 6 L/min is appropriate because the patient's SpO2 is currently 92 percent, which is at the lower limit of acceptable for a patient three days post anterior wall myocardial infarction. Normal SpO2 should ideally be ≥ 94 percent in cardiac patients to ensure adequate myocardial oxygenation. Increasing the fraction of inspired oxygen helps reduce the workload of the heart and may decrease the frequency of ectopy caused by localized areas of myocardial hypoxia.
Choice C rationale
Administering 40 mEq of potassium chloride is inappropriate for this specific patient because her potassium level is 4.4 mEq/L, which falls perfectly within the normal physiological range of 3.5 to 5.0 mEq/L. Over-supplementing potassium when the serum level is already optimal carries a significant risk of inducing hyperkalemia. Excessive potassium can lead to lethal arrhythmias, such as ventricular fibrillation or asystole, by disrupting the resting membrane potential and interfering with cardiac repolarization.
Choice D rationale
Lidocaine 100 mg IV push is a standard pharmacological intervention for a patient experiencing frequent or multifocal premature ventricular contractions following an acute myocardial infarction. Lidocaine is a Class IB antiarrhythmic that works by blocking fast voltage-gated sodium channels, particularly in ischemic tissues. This action shortens the action potential duration and raises the fibrillation threshold, thereby suppressing ventricular ectopy and preventing the progression to more dangerous rhythms like ventricular tachycardia or ventricular fibrillation.
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