MCQs on ABG Analysis

MCQs on ABG Analysis Model Questions

Here’s a comprehensive set of multiple-choice questions (MCQs) covering Arterial Blood Gas (ABG) analysis from basic to super-hard levels, with the answer key at the end.

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MCQs on ABG Analysis

Basic Level

1. What is the normal pH range of arterial blood?
   a) 7.0 – 7.2
   b) 7.35 – 7.45
   c) 7.5 – 7.8
   d) 6.8 – 7.0

2. The primary buffer system used to maintain blood pH is:
   a) Phosphate buffer system
   b) Protein buffer system
   c) Bicarbonate-carbonic acid buffer system
   d) Hemoglobin buffer system

3. In respiratory acidosis, which of the following is typically increased?
   a) pH
   b) PaCO₂
   c) HCO₃⁻
   d) Oxygen saturation

4. Which of the following ABG values is most consistent with metabolic acidosis?
   a) pH = 7.50, PaCO₂ = 30 mmHg, HCO₃⁻ = 24 mEq/L
   b) pH = 7.20, PaCO₂ = 40 mmHg, HCO₃⁻ = 15 mEq/L
   c) pH = 7.38, PaCO₂ = 42 mmHg, HCO₃⁻ = 26 mEq/L
   d) pH = 7.28, PaCO₂ = 55 mmHg, HCO₃⁻ = 24 mEq/L

5. Respiratory alkalosis occurs due to:
   a) Hyperventilation
   b) Hypoventilation
   c) Increased bicarbonate loss
   d) Excess acid production

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Intermediate Level

6. A compensatory mechanism for metabolic acidosis is:
   a) Decreased respiratory rate
   b) Increased bicarbonate reabsorption
   c) Increased respiratory rate
   d) Decreased bicarbonate reabsorption

7. Which of the following ABG values is most consistent with fully compensated metabolic acidosis?
   a) pH = 7.40, PaCO₂ = 30 mmHg, HCO₃⁻ = 18 mEq/L
   b) pH = 7.32, PaCO₂ = 48 mmHg, HCO₃⁻ = 24 mEq/L
   c) pH = 7.28, PaCO₂ = 50 mmHg, HCO₃⁻ = 26 mEq/L
   d) pH = 7.50, PaCO₂ = 28 mmHg, HCO₃⁻ = 26 mEq/L

8. In chronic respiratory acidosis, which compensatory mechanism occurs?
   a) Decreased bicarbonate excretion by kidneys
   b) Increased bicarbonate reabsorption by kidneys
   c) Increased ventilation
   d) Decreased ventilation

9. Which of the following conditions is a cause of anion gap metabolic acidosis?
   a) Diabetic ketoacidosis
   b) Vomiting
   c) Renal tubular acidosis
   d) Hypoaldosteronism

10. What is the normal anion gap range in arterial blood gas analysis?
    a) 6 – 12 mEq/L
    b) 12 – 18 mEq/L
    c) 18 – 24 mEq/L
    d) 24 – 30 mEq/L

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Advanced Level

11. Which formula is used to calculate the anion gap?
    a) (Na⁺ + K⁺) – (Cl⁻ + HCO₃⁻)
    b) (Na⁺) – (Cl⁻ + HCO₃⁻)
    c) (Na⁺ + Cl⁻) – (K⁺ + HCO₃⁻)
    d) (K⁺ + Cl⁻) – (Na⁺ + HCO₃⁻)

12. A pH of 7.30, PaCO₂ of 28 mmHg, and HCO₃⁻ of 12 mEq/L suggests which condition?
    a) Uncompensated metabolic acidosis
    b) Partially compensated metabolic acidosis
    c) Fully compensated metabolic alkalosis
    d) Uncompensated respiratory acidosis

13. The Winter’s formula is used to determine:
    a) Expected PaCO₂ in metabolic acidosis
    b) Expected HCO₃⁻ in metabolic alkalosis
    c) Anion gap correction in hypoalbuminemia
    d) Mixed acid-base disorders

14. If a patient has metabolic acidosis with a normal anion gap, which is the most likely cause?
    a) Lactic acidosis
    b) Diabetic ketoacidosis
    c) Hyperchloremia
    d) Methanol poisoning

15. Which of the following values is typically found in acute respiratory acidosis?
    a) pH = 7.55, PaCO₂ = 25 mmHg, HCO₃⁻ = 22 mEq/L
    b) pH = 7.32, PaCO₂ = 55 mmHg, HCO₃⁻ = 24 mEq/L
    c) pH = 7.40, PaCO₂ = 40 mmHg, HCO₃⁻ = 24 mEq/L
    d) pH = 7.50, PaCO₂ = 30 mmHg, HCO₃⁻ = 24 mEq/L

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Super-Hard Level

16. A patient has pH = 7.20, PaCO₂ = 40 mmHg, HCO₃⁻ = 12 mEq/L, and an anion gap of 25 mEq/L. What additional parameter is crucial to check?
    a) Delta gap to assess mixed disorders
    b) Serum potassium level
    c) Lactate level
    d) Serum sodium level

17. Which of the following indicates a mixed acid-base disorder?
    a) pH = 7.35, PaCO₂ = 50 mmHg, HCO₃⁻ = 32 mEq/L
    b) pH = 7.28, PaCO₂ = 60 mmHg, HCO₃⁻ = 26 mEq/L
    c) pH = 7.40, PaCO₂ = 40 mmHg, HCO₃⁻ = 24 mEq/L
    d) pH = 7.50, PaCO₂ = 30 mmHg, HCO₃⁻ = 26 mEq/L

18. In high anion gap metabolic acidosis, which correction must be made if albumin is low?
    a) Corrected anion gap = Observed anion gap + (2.5 × [4 – albumin])
    b) Corrected anion gap = Observed anion gap – (2 × albumin)
    c) Corrected anion gap = Observed anion gap × (albumin / 4)
    d) No correction is needed

19. A patient with COPD has pH = 7.35, PaCO₂ = 60 mmHg, HCO₃⁻ = 32 mEq/L. What does this indicate?
    a) Acute respiratory acidosis
    b) Chronic respiratory acidosis with compensation
    c) Metabolic alkalosis with compensation
    d) Respiratory alkalosis

20. The expected PaCO₂ in metabolic acidosis can be calculated using:
    a) (1.5 × HCO₃⁻) + 8 ± 2
    b) (HCO₃⁻ × 2) + 10 ± 5
    c) (PaO₂ / HCO₃⁻) + 5
    d) (PaCO₂ / HCO₃⁻) × 0.7

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Answer Key

1. b
2. c
3. b
4. b
5. a
6. c
7. a
8. b
9. a
10. a
11. b
12. b
13. a
14. c
15. b
16. a
17. b
18. a
19. b
20. a