The nurse preceptor is teaching about the physiology of the fetal heart rate (FHR) pattern. Which statement by the student indicates a lack of understanding?
Vagus nerve stimulation increases FHR variability.
Baroreceptors are responsible for regulating blood pressure.
The autonomic nervous system controls the FHR.
Chemoreceptors respond to changes in blood gas levels.
The Correct Answer is A
Choice A rationale
This statement is incorrect. Vagus nerve stimulation actually decreases FHR variability. The vagus nerve, part of the parasympathetic nervous system, slows the heart rate and reduces variability.
Choice B rationale
This statement is correct. Baroreceptors are sensors located in blood vessels that help regulate blood pressure by detecting changes in the stretch of the vessel walls. They play a crucial role in maintaining stable blood pressure levels.
Choice C rationale
This statement is correct. The autonomic nervous system, which includes the sympathetic and parasympathetic nervous systems, controls the fetal heart rate. It regulates the balance between heart rate acceleration and deceleration.
Choice D rationale
This statement is correct. Chemoreceptors respond to changes in blood gas levels, such as oxygen and carbon dioxide. They help regulate respiratory and cardiovascular responses to maintain homeostasis.
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Correct Answer is A
Explanation
Choice A rationale
Terbutaline is a beta-adrenergic agonist that works by relaxing the smooth muscles of the uterus, thereby reducing uterine contractions. It is commonly used in cases of tachysystole and recurrent late decelerations to decrease uterine activity and improve fetal oxygenation. Terbutaline’s mechanism of action involves stimulating beta-2 adrenergic receptors, which leads to an increase in cyclic AMP and subsequent relaxation of uterine smooth muscle.
Choice B rationale
Oxytocin is a hormone that stimulates uterine contractions and is typically used to induce or augment labor. Administering oxytocin in a situation where there is already tachysystole and recurrent late decelerations would exacerbate the problem by increasing uterine contractions, potentially leading to further fetal distress.
Choice C rationale
Misoprostol is a prostaglandin analog used to ripen the cervix and induce labor. Similar to oxytocin, it would not be appropriate in this scenario as it would increase uterine contractions, worsening the tachysystole and late decelerations.
Choice D rationale
Magnesium sulfate is primarily used as a tocolytic to prevent preterm labor and as a neuroprotective agent for the fetus in cases of preeclampsia. While it has some uterine relaxation properties, it is not the first-line treatment for reducing uterine activity in the context of tachysystole and late decelerations.
Correct Answer is B
Explanation
Choice A rationale
Early decelerations are characterized by a gradual decrease and return to baseline of the fetal heart rate that coincides with the peak of a contraction. They are typically benign and related to fetal head compression.
Choice B rationale
Late decelerations are characterized by a gradual decrease and return to baseline of the fetal heart rate that occurs after the peak of a contraction. They are associated with uteroplacental insufficiency and require prompt intervention to improve fetal oxygenation.
Choice C rationale
Variable decelerations are characterized by an abrupt decrease in fetal heart rate that varies in duration, intensity, and timing relative to contractions. They are often caused by umbilical cord compression and may require interventions to relieve the compression.
Choice D rationale
Prolonged decelerations are characterized by a decrease in fetal heart rate that lasts longer than 2 minutes but less than 10 minutes. They indicate a more severe and sustained disruption in fetal oxygenation and require immediate intervention.