NBRC Critical Care and ABG Interpretation 1 — Questions and Answers
Question 1: A patient has ABG values: pH 7.28, PaCO2 55 mmHg, HCO3 24 mEq/L. This represents:
- Metabolic acidosis
- Respiratory acidosis (uncompensated) (Correct answer)
- Metabolic alkalosis
- Respiratory alkalosis
Correct answer: Respiratory acidosis (uncompensated)
pH below 7.35 (acidosis) with elevated PaCO2 and normal HCO3 indicates uncompensated acute respiratory acidosis.
Question 2: A patient has ABG: pH 7.52, PaCO2 28 mmHg, HCO3 22 mEq/L. This is consistent with:
- Metabolic alkalosis
- Respiratory alkalosis (uncompensated) (Correct answer)
- Compensated respiratory acidosis
- Normal values
Correct answer: Respiratory alkalosis (uncompensated)
pH above 7.45 (alkalosis) with low PaCO2 and near-normal HCO3 indicates uncompensated acute respiratory alkalosis from hyperventilation.
Question 3: Acute hypoxemic respiratory failure is defined by a PaO2/FiO2 (P/F) ratio below:
- 400
- 300 (Correct answer)
- 200
- 100
Correct answer: 300
A P/F ratio below 300 mmHg defines acute hypoxemic respiratory failure; values below 200 define ARDS and below 100 define severe ARDS (Berlin criteria).
Question 4: In diabetic ketoacidosis (DKA), the respiratory compensation (Kussmaul respirations) produces:
- Respiratory acidosis
- Respiratory alkalosis to compensate for metabolic acidosis (Correct answer)
- No change in PaCO2
- Metabolic alkalosis
Correct answer: Respiratory alkalosis to compensate for metabolic acidosis
Kussmaul respirations are deep, rapid breaths that blow off CO2, lowering PaCO2 to partially compensate for the metabolic acidosis of DKA.
Question 5: The anion gap is calculated as:
- Na+ – (Cl– + HCO3–) (Correct answer)
- Na+ + K+ – (Cl– + HCO3–)
- Cl– – HCO3–
- Na+ – K+
Correct answer: Na+ – (Cl– + HCO3–)
The anion gap = Na+ – (Cl– + HCO3–); a normal anion gap is 8–12 mEq/L, and an elevated gap indicates unmeasured anions from conditions like lactic acidosis or DKA.
Question 6: Which of the following causes a high anion gap metabolic acidosis?
- Diarrhea
- Renal tubular acidosis
- Lactic acidosis (Correct answer)
- Excessive chloride infusion
Correct answer: Lactic acidosis
Lactic acidosis increases unmeasured anions (lactate), elevating the anion gap, unlike hyperchloremic (normal anion gap) acidoses such as diarrhea or RTA.
NBRC Critical Care and ABG Interpretation 1
A patient has ABG values: pH 7.28, PaCO2 55 mmHg, HCO3 24 mEq/L.
This represents: