Given the arterial blood gas values pH 7.2, CO2 34, HCO3- 14, Na 135, Cl 95, calculate the base deficit from these data.

Given the arterial blood gas values pH 7.2, CO2 34, HCO3- 14, Na 135, Cl 95, calculate the base deficit from these data.

• A. -5
• B. -13
• C. -20
• D. -25

Answer: (B)

Base deficit is a way to quantify the metabolic component of an acid-base disturbance by looking at the anion gap. First, calculate the anion gap: Na − (Cl + HCO3) = 135 − (95 + 14) = 26 mEq/L. Normal anion gap is about 12; the excess is roughly 14. The base deficit (metabolic acid burden) roughly corresponds to this excess, so about 14 mEq/L, and since acidosis implies a deficit, it is negative: about −14. Among the given choices, −13 is the closest value. Note that the pCO2 is slightly higher than expected for a pure metabolic acidosis, suggesting a small concurrent respiratory acidosis, but the base deficit calculation here reflects the metabolic component.

Base deficit is a way to quantify the metabolic component of an acid-base disturbance by looking at the anion gap. First, calculate the anion gap: Na − (Cl + HCO3) = 135 − (95 + 14) = 26 mEq/L. Normal anion gap is about 12; the excess is roughly 14. The base deficit (metabolic acid burden) roughly corresponds to this excess, so about 14 mEq/L, and since acidosis implies a deficit, it is negative: about −14. Among the given choices, −13 is the closest value. Note that the pCO2 is slightly higher than expected for a pure metabolic acidosis, suggesting a small concurrent respiratory acidosis, but the base deficit calculation here reflects the metabolic component.