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Chapter 36. Acid–Base Disorders

A 35-year-old woman is in the intensive care unit, intubated after a recent abdominal surgery. While in the operating room, she received more than 8 L of fluid and blood products, but has been aggressively diuresed since that time. In the past 3 days she has generated 6 L of urine output, her BUN and Cr have increased to 35 mg/dL and 1.4 mg/dL, respectively (baseline of 10 mg/dL and 0.7 mg/dL), and her blood pressure has decreased to 100/60 mm Hg. This morning, her ABG shows the following: pH 7.50, PaCO2 48 mm Hg, and HCO3 37 mEq/L.

Which of the primary acid–base disturbances is present in this patient?

a. Metabolic acidosis

b. Metabolic alkalosis

c. Respiratory acidosis

d. Respiratory alkalosis

Answer b is correct. The pH is elevated, indicating alkalosis, and the bicarbonate more than 28, indicating metabolic alkalosis.

Answers a and c are incorrect. The pH is alkalemic; therefore, acidosis can be excluded.

Answer d is incorrect. The PaCO2 >40 mm Hg which would be inappropriate for a respiratory alkalosis. The patient has a metabolic alkalosis secondary to over-diuresis which has led to volume contraction.

A 35-year-old woman is in the intensive care unit, intubated after a recent abdominal surgery. While in the operating room, she received more than 8 L of fluid and blood products, but has been aggressively diuresed since that time. In the past 3 days she has generated 6 L of urine output, her BUN and Cr have increased to 35 mg/dL and 1.4 mg/dL, respectively (baseline of 10 mg/dL and 0.7 mg/dL), and her blood pressure has decreased to 100/60 mm Hg. This morning, her ABG shows the following: pH 7.50, PaCO2 48 mm Hg, and HCO3 37 mEq/L.

Has the patient appropriately compensated for the primary disorder?

a. Yes, the PaCO2 is elevated, indicating appropriate compensation.

b. Yes, the HCO3 is elevated, indicating appropriate compensation.

c. No, the HCO3 is low, indicating the patient has not yet been compensated.

d. No, the PaCO2 is low, indicating the patient has not yet been compensated.

Answer a is correct. In metabolic alkalosis we would expect the PaCO2 to be elevated as compensation to hold on to acid.

Answers b and c are incorrect. The patient does ...

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