What is the primary reason for increased tidal volume during pregnancy?
Decreased oxygen demand
Progesterone’s effect on the respiratory center
Increased functional residual capacity
Reduced chest wall compliance
The Correct Answer is B
Respiratory changes in pregnancy are driven mainly by the hormonal influence of progesterone on the respiratory center in the medulla. Progesterone increases sensitivity to carbon dioxide, lowering arterial PaCO₂ to 27–32 mmHg (normal 35–45 mmHg). This causes increased tidal volume and minute ventilation, ensuring adequate maternal oxygen delivery and fetal gas exchange despite unchanged respiratory rate.
Rationale for correct answer
2. Progesterone stimulates the central respiratory center, increasing sensitivity to carbon dioxide. This leads to deeper breaths, thereby increasing tidal volume and maternal minute ventilation, which supports enhanced oxygen transfer to the fetus.
Rationale for incorrect answers
1. Oxygen demand does not decrease in pregnancy; instead, it increases by about 20–30% due to fetal and maternal metabolic requirements. Therefore, decreased oxygen demand is not a cause of increased tidal volume.
3. Functional residual capacity decreases by about 20% during pregnancy because the enlarged uterus elevates the diaphragm. A reduced FRC does not cause increased tidal volume; rather, it reflects decreased lung volumes.
4. Chest wall compliance is not reduced in pregnancy. Rib cage expansion actually increases chest wall dimensions to accommodate the growing uterus, and this adaptation does not explain the rise in tidal volume.
Take home points
• Progesterone stimulates the maternal respiratory center, causing hyperventilation in pregnancy.
• Arterial PaCO₂ decreases to 27–32 mmHg as a normal pregnancy adaptation.
• Tidal volume and minute ventilation increase, but respiratory rate remains largely unchanged.
• Oxygen demand increases by 20–30% during pregnancy to meet maternal and fetal needs.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is C
Explanation
Physiological anemia in pregnancyis caused by an increased plasma volumerelative to red blood cell mass. Plasma volume expands by 40–50% while red blood cell mass rises only 20–30%, leading to hemodilution. The normal hemoglobin range in pregnancy is 11–13 g/dL, and hematocrit falls to 32–36%. This adaptation enhances uteroplacental perfusion but predisposes to symptoms like fatigueand paleness.
Rationale for correct answer
3.Plasma volume increases more than red blood cell mass, resulting in hemodilution and relative anemia. This explains the physiological anemia observed during pregnancy, which ensures optimal placental perfusion without true reduction in oxygen-carrying capacity.
Rationale for incorrect answers
1.Increased red blood cell mass does occur, but it is not sufficient to match the larger plasma volume expansion. Therefore, while it increases oxygen delivery, it does not cause anemia.
2.Decreased plasma volume is opposite of what occurs in pregnancy. Plasma volume expands significantly under estrogen and aldosterone influence, ensuring greater blood flow to the placenta.
4.Cardiac output increases by 30–50% in pregnancy due to increased stroke volume and heart rate. This enhances systemic and placental circulation but does not directly explain anemia.
Take home points
• Physiological anemia in pregnancy results from disproportionate plasma volume expansion.
• Hemoglobin values normally fall to 11–13 g/dL, hematocrit to 32–36% in pregnancy.
• Cardiac output and blood volume increase but oxygen-carrying capacity is maintained.
• Differentiate physiological anemia from iron-deficiency anemia, which lowers hemoglobin below 11 g/dL.
Correct Answer is B
Explanation
Nasal congestion in pregnancyis primarily caused by estrogen-induced hyperemiaof the mucous membranes. Estrogen increases vascular engorgementand capillary permeability, leading to nasal stuffiness, epistaxis, and a sensation of obstruction. Normal blood volume increases by 40–50% during pregnancy, which enhances mucosal vascularity, further worsening nasal congestion. These changes are benign but commonly distressing to clients.
Rationale for correct answer
2.Estrogen increases vascular engorgement and hyperemia of the nasal mucosa. This leads to increased swelling and fragility of capillaries, causing stuffiness and frequent nosebleeds as a normal physiological change in pregnancy.
Rationale for incorrect answers
1.Blood volume does not decrease in pregnancy; instead, it increases by 40–50%. A decrease in blood volume would cause hypotension and poor perfusion, not nasal congestion or epistaxis.
3.Respiratory rate does not significantly decrease in pregnancy. It usually remains stable, while tidal volume increases. A reduced rate would impair gas exchange but does not cause nasal congestion or bleeding.
4.Increased clotting factors are a hematological change of pregnancy to reduce postpartum hemorrhage risk. While this creates a hypercoagulable state, it does not cause nasal stuffiness or epistaxis.
Take home points
• Estrogen increases nasal mucosal vascularity, causing congestion and nosebleeds in pregnancy.
• Blood volume increases 40–50% and contributes to mucosal engorgement.
• Respiratory rate remains stable, but tidal volume increases due to progesterone.
• Hypercoagulability in pregnancy prevents hemorrhage but does not cause nasal symptoms.
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