A 20-year-old, 75-kg patient with diabetic ketoacidosis presents with ABG on room air: pH 6.95, PaCO2 30 mm Hg, PaO2 98 mm Hg, HCO3- 6 mEq/L. What is the total body deficit of HCO3-?

A 20-year-old, 75-kg patient with diabetic ketoacidosis presents with ABG on room air: pH 6.95, PaCO2 30 mm Hg, PaO2 98 mm Hg, HCO3- 6 mEq/L. What is the total body deficit of HCO3-?

• A. 500 mEq
• B. 400 mEq
• C. 300 mEq
• D. 200 mEq

Answer: (B)

In metabolic acidosis like diabetic ketoacidosis, the total body bicarbonate deficit is estimated from how much the HCO3- is lowered and the volume in which bicarbonate is distributed, mainly the extracellular fluid. Start with the deficit per liter: normal HCO3- is about 24 mEq/L, and the patient’s HCO3- is 6 mEq/L, so the deficit is 24 − 6 = 18 mEq/L. The extracellular fluid volume is roughly 0.3 L per kilogram, so for a 75‑kg person that’s 0.3 × 75 = 22.5 liters. Multiply the deficit per liter by the extracellular fluid volume: 18 mEq/L × 22.5 L ≈ 405 mEq. This is about 400 mEq of total body bicarbonate deficit, which matches the given answer.

In metabolic acidosis like diabetic ketoacidosis, the total body bicarbonate deficit is estimated from how much the HCO3- is lowered and the volume in which bicarbonate is distributed, mainly the extracellular fluid. Start with the deficit per liter: normal HCO3- is about 24 mEq/L, and the patient’s HCO3- is 6 mEq/L, so the deficit is 24 − 6 = 18 mEq/L. The extracellular fluid volume is roughly 0.3 L per kilogram, so for a 75‑kg person that’s 0.3 × 75 = 22.5 liters. Multiply the deficit per liter by the extracellular fluid volume: 18 mEq/L × 22.5 L ≈ 405 mEq. This is about 400 mEq of total body bicarbonate deficit, which matches the given answer.