Question 1

Which of the following best describes the physiologic relationship governing blood pH?

 

A. pH is proportional to PaCO₂/HCO₃⁻

B. pH is proportional to HCO₃⁻/PaCO₂

C. pH depends only on PaCO₂

D. pH depends only on HCO₃⁻

E. pH is proportional to HCO₃⁻ × PaCO₂

​

Question 2

Which statement regarding acid–base disorders is correct?

 

A. Normal pH excludes an acid–base disorder

B. Compensation often overshoots the primary disorder

C. Normal pH can occur in mixed acid–base disorders

D. Anion gap calculation is unnecessary in metabolic acidosis

E. Respiratory disorders compensate immediately

 

Question 3

Which of the following best describes the relationship between pH and bicarbonate in primary metabolic disorders?

 

A. pH and PaCO₂ move in the same direction

B. pH and HCO₃⁻ move in opposite directions

C. pH and HCO₃⁻ move in the same direction

D. pH is independent of bicarbonate

E. Bicarbonate remains unchanged

 

Question 4

Which of the following best defines the anion gap?

 

A. Na⁺ − Cl⁻

B. (Na⁺ + Ca⁺) − (Cl⁻ + HCO₃⁻)

C. Na⁺ − HCO₃⁻

D. Cl⁻ − HCO₃⁻

E. Na⁺ − (Cl⁻ + HCO₃⁻)

​

Question 5

Which of the following conditions can falsely decrease the measured anion gap?

 

A. Hyperkalemia

B. Hypophosphatemia

C. Hypoalbuminemia

D. Hypernatremia

E. Metabolic alkalosis

​

Question 6

Which formula is used to estimate expected respiratory compensation in metabolic acidosis?

 

A. PaCO₂ = HCO₃⁻ + 8

B. PaCO₂ = (1.5 × HCO₃⁻) + 8 ± 2

C. PaCO₂ = (2 × HCO₃⁻) + 10

D. PaCO₂ = (HCO₃⁻ ÷ 2) + 8

E. PaCO₂ = constant

 

Question 7

If the measured PaCO₂ in metabolic acidosis is higher than predicted by Winter’s formula, which of the following is present?

 

A. Appropriate compensation

B. Respiratory alkalosis

C. Respiratory acidosis

D. Metabolic alkalosis

E. Mixed metabolic acidosis

 

Question 8

Which of the following best describes the expected compensation in metabolic alkalosis?

 

A. PaCO₂ decreases by 1 mmHg for every 1 mEq/L rise in HCO₃⁻

B. PaCO₂ increases by ~0.6–0.7 mmHg for every 1 mEq/L rise in HCO₃⁻

C. PaCO₂ remains unchanged

D. PaCO₂ increases by 2 mmHg for each 1 mEq/L rise in HCO₃⁻

E. PaCO₂ doubles with alkalosis

 

Question 9

Delta–delta analysis is primarily used to detect which of the following?

 

A. Respiratory compensation

B. Additional metabolic disorders

C. Primary respiratory acidosis

D. Hyperkalemia

E. Chloride imbalance

 

Question 10

The “1–2–4–5 rule” is used to evaluate compensation in which type of disorder?

 

A. Metabolic acidosis

B. Metabolic alkalosis

C. Respiratory disorders

D. Mixed metabolic disorders

E. Lactic acidosis

 

Question 11

A patient has pH 7.25, PaCO₂ 20 mmHg, and HCO₃⁻ 12 mEq/L. Which of the following best explains these findings?

 

A. Pure metabolic acidosis

B. Pure respiratory alkalosis

C. Metabolic acidosis with respiratory compensation

D. Mixed metabolic acidosis and respiratory alkalosis

E. Mixed metabolic alkalosis and respiratory acidosis

 

Question 12

In a patient with high anion gap metabolic acidosis, the ΔAG is 14 and ΔHCO₃⁻ is 6. Which interpretation is correct?

 

A. Pure high anion gap metabolic acidosis

B. HAGMA with respiratory alkalosis

C. Pure metabolic alkalosis

D. HAGMA with non-gap metabolic acidosis

E. HAGMA with metabolic alkalosis

 

Question 13

A patient with metabolic acidosis has HCO₃⁻ of 10 mEq/L. Winter’s formula predicts PaCO₂ ≈ 23 mmHg, but the measured PaCO₂ is 40 mmHg. What does this indicate?

 

A. Appropriate respiratory compensation

B. Respiratory alkalosis

C. Respiratory acidosis

D. Concurrent metabolic alkalosis

E. Chronic respiratory compensation

 

Question 14

A 14-year-old boy presents with 3 days of vomiting due to viral gastroenteritis. Laboratory studies show pH 7.52, PaCO₂ 48 mmHg, and HCO₃⁻ 38 mEq/L. Which acid–base disorder is most likely present?

 

A. Metabolic alkalosis with appropriate respiratory compensation

B. Metabolic acidosis

C. Respiratory alkalosis

D. Respiratory acidosis

E. Mixed metabolic acidosis and respiratory alkalosis

 

Question 15

A 16-year-old girl with type 1 diabetes presents with abdominal pain and tachypnea. Labs show pH 7.18, PaCO₂ 22 mmHg, and HCO₃⁻ 8 mEq/L. Which primary disorder is most likely to be present?

 

A. Respiratory acidosis

B. Metabolic alkalosis

C. High anion gap metabolic acidosis

D. Respiratory alkalosis

E. Non–anion gap metabolic acidosis

 

Question 16

A 13-year-old boy with severe diarrhea has pH 7.30, PaCO₂ 32 mmHg, and HCO₃⁻ 16 mEq/L. What is the most likely acid–base disorder?

 

A. Respiratory alkalosis

B. Non–anion gap metabolic acidosis with respiratory compensation

C. High anion gap metabolic acidosis

D. Metabolic alkalosis

E. Respiratory acidosis

 

Question 17

A 15-year-old girl presents with anxiety and rapid breathing. Labs show pH 7.55, PaCO₂ 25 mmHg, and HCO₃⁻ 22 mEq/L. Which disorder is most likely?

 

A. Respiratory alkalosis

B. Metabolic alkalosis

C. Respiratory acidosis

D. Metabolic acidosis

E. Mixed metabolic alkalosis and respiratory acidosis

 

Question 18

A 17-year-old boy with chronic lung disease has pH 7.35, PaCO₂ 60 mmHg, and HCO₃⁻ 33 mEq/L. Which condition best explains these findings?

 

A. Acute respiratory alkalosis

B. Chronic respiratory acidosis with metabolic compensation

C. Acute metabolic acidosis

D. Metabolic alkalosis

E. Mixed respiratory alkalosis and metabolic acidosis

 

Question 19

A 12-year-old boy presents with confusion after ingesting antifreeze. Labs show pH 7.10, HCO₃⁻ 10 mEq/L, and an anion gap of 28. What is the most likely acid–base disorder?

 

A. Non–anion gap metabolic acidosis

B. High anion gap metabolic acidosis

C. Respiratory alkalosis

D. Metabolic alkalosis

E. Respiratory acidosis

 

Question 20

A 14-year-old girl presents with salicylate toxicity. Labs show pH 7.45, PaCO₂ 25 mmHg, and HCO₃⁻ 17 mEq/L. Which acid–base disorder is most consistent with these findings?

​

A. Pure respiratory alkalosis

B. Pure metabolic acidosis

C. Mixed respiratory alkalosis and metabolic acidosis

D. Metabolic alkalosis

E. Respiratory acidosis

 

Answer Key

Question 1: B

​

Question 2: C

​

Question 3: C

 

Question 4: E

 

Question 5: C

 

Question 6: B

 

Question 7: C

 

Question 8: B

 

Question 9: B

 

Question 10: C

 

Question 11: D

 

Question 12: E

 

Question 13: C

 

Question 14: A. Vomiting causes loss of gastric acid leading to metabolic alkalosis. Hypoventilation increases PaCO₂ as respiratory compensation.

 

Question 15: C : Diabetic ketoacidosis produces accumulation of ketone bodies, leading to high anion gap metabolic acidosis.

​

Question 16: B. Loss of bicarbonate in stool causes non–anion gap metabolic acidosis. Respiratory compensation lowers PaCO₂.

​

Question 17: A: Hyperventilation lowers PaCO₂, producing respiratory alkalosis.

​

Question 18: B: Chronic CO₂ retention leads to renal bicarbonate retention, producing metabolic compensation for respiratory acidosis.

​

Question 19: B: Ethylene glycol ingestion produces toxic metabolites that generate a high anion gap metabolic acidosis.

​

Question 20: C: Salicylates cause a mixed disorder: respiratory alkalosis from central respiratory stimulation and metabolic acidosis from organic acid accumulation.