Chapter 36: Acid–Base Disorders

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 blood urea nitrogen (BUN) and creatinine (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 arterial blood gas (ABG) shows the following: pH 7.50, P_aCO₂ 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 is 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 P_aCO₂ is above 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 blood urea nitrogen (BUN) and creatinine (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 arterial blood gas (ABG) shows the following: pH 7.50, P_aCO₂ 48 mm Hg, and HCO₃ 37 mEq/L.

Has the patient appropriately compensated for the primary disorder?

a. Yes, the P_aCO₂ 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 P_aCO₂ is low, indicating the patient has not yet been compensated.

Answer a is correct. In metabolic alkalosis we would expect the P_aCO₂ to be elevated as compensation to hold on ...