What acid-base disturbance is seen in pregnancy due to ventilation changes?

What acid-base disturbance is seen in pregnancy due to ventilation changes?

• A. Metabolic acidosis
• B. Normal compensated respiratory alkalosis
• C. Metabolic alkalosis
• D. Respiratory acidosis

Answer: (B)

In pregnancy, ventilation increases due to hormonal effects, especially progesterone, which lowers arterial CO2 and creates a mild respiratory alkalosis. The body then compensates by the kidneys eliminating bicarbonate, which brings the pH back toward normal but with a reduced bicarbonate level. The result is a near-normal pH with low CO2 and low bicarbonate, described as a normal compensated respiratory alkalosis. This is why the best answer reflects a compensated respiratory alkalosis rather than a primary metabolic or respiratory disturbance. Metabolic acidosis would show low pH with low bicarbonate, metabolic alkalosis would raise pH with high bicarbonate, and respiratory acidosis would show elevated CO2 with acidemia; none of those align with the compensated alkalemic state seen in pregnancy. Typical ABG pattern to remember: pH near normal, PaCO2 reduced (around 30 mmHg), bicarbonate modestly decreased due to renal compensation.

In pregnancy, ventilation increases due to hormonal effects, especially progesterone, which lowers arterial CO2 and creates a mild respiratory alkalosis. The body then compensates by the kidneys eliminating bicarbonate, which brings the pH back toward normal but with a reduced bicarbonate level. The result is a near-normal pH with low CO2 and low bicarbonate, described as a normal compensated respiratory alkalosis. This is why the best answer reflects a compensated respiratory alkalosis rather than a primary metabolic or respiratory disturbance. Metabolic acidosis would show low pH with low bicarbonate, metabolic alkalosis would raise pH with high bicarbonate, and respiratory acidosis would show elevated CO2 with acidemia; none of those align with the compensated alkalemic state seen in pregnancy. Typical ABG pattern to remember: pH near normal, PaCO2 reduced (around 30 mmHg), bicarbonate modestly decreased due to renal compensation.