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Zorluk: KolayNormal Pregnancy and Prenatal Care

An expectant mother, age 30, is brought to the emergency department at 28 weeks gestation following a minor traffic accident. She reports no abdominal pain, vaginal bleeding, or shortness of breath. She has no significant medical history and takes only a daily prenatal vitamin. Vital signs show a blood pressure of 110/70110/70 mm Hg, pulse of 8888/min, and respiratory rate of 1616/min. Continuous fetal heart rate monitoring is reassuring. As part of a standard trauma protocol, an arterial blood gas is obtained on room air. Compared to a healthy nonpregnant state, which of the following acid-base profiles is an expected physiological finding in this patient?

  1. Primary respiratory alkalosis with metabolic compensationCevap
  2. B
    Primary metabolic acidosis with respiratory compensation
  3. C
    Primary respiratory acidosis with metabolic compensation
  4. D
    Primary metabolic alkalosis with respiratory compensation
  5. E
    Uncompensated respiratory alkalosis with normal serum bicarbonate

Cevap

Primary respiratory alkalosis with metabolic compensation
The correct answer accurately reflects the physiologic effect of elevated progesterone during normal pregnancy. Progesterone directly stimulates the medullary respiratory center, which increases tidal volume (with a relatively unchanged respiratory rate) and boosts overall minute ventilation. This physiologic hyperventilation increases the exhalation of carbon dioxide, dropping the PaCO2PaCO_2 (often to 28-32 mm Hg) and creating a primary respiratory alkalosis. Because this is a chronic and progressive state, the kidneys have weeks to fully compensate by excreting more HCO3−HCO_3^-, leading to a mild decrease in serum bicarbonate. The resulting blood gas typical of a normal pregnancy shows a compensated respiratory alkalosis with a slightly basic pH.

Adım Adım Çözüm

1
Identify the primary physiologic stimulus on maternal respiration during pregnancy.
Elevated progesterone levels directly stimulate the central respiratory center, leading to an increase in tidal volume and overall minute ventilation.
This fundamental adaptation helps meet the increased metabolic and oxygen demands of the growing fetus and maternal tissues.
2
Determine the resulting primary acid-base disturbance.
The chronic increase in minute ventilation causes a continuous washout of carbon dioxide, lowering the PaCO2PaCO_2 and resulting in a primary respiratory alkalosis.
Decreased carbon dioxide shifts the equilibrium in the blood, effectively reducing the hydrogen ion concentration.
3
Evaluate the compensatory renal response to the primary disturbance.
Because pregnancy is a prolonged state, the kidneys have ample time to fully compensate by increasing the excretion of HCO3−HCO_3^-.
Metabolic compensation prevents the pH from becoming dangerously alkaline, maintaining it in a high-normal range (typically pH 7.40 to 7.44).

Anahtar Kavram

During normal pregnancy, elevated progesterone levels stimulate the respiratory center, increasing minute ventilation and causing a chronic primary respiratory alkalosis that is compensated by increased renal excretion of bicarbonate.
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Normal Pregnancy and Prenatal Care

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