COMSAE PHASE 1 ACID-BASE DISORDERS
PRACTICE EXAM WITH QUESTIONS AND
VERIFIED ANSWERS, PLUS DETAILED
RATIONALES/EXPERT VERIFIED FOR
GUARANTEED PASS 2026/LATEST
UPDATE/INSTANT DOWNLOAD PDF
Question 1
A 23-year-old woman with type 1 diabetes mellitus presents with
nausea, vomiting, abdominal pain, and progressively increasing lethargy.
She has been unable to obtain insulin for 2 days. Her respiratory rate is
30/min with deep respirations. Laboratory studies show:
Na⁺: 138 mEq/L
Cl⁻: 100 mEq/L
HCO₃⁻: 10 mEq/L
Glucose: 420 mg/dL
Arterial blood gas:
pH: 7.18
PaCO₂: 24 mm Hg
Which of the following best describes this patient's acid-base disorder?
A. Respiratory acidosis with metabolic compensation
B. Metabolic acidosis with appropriate respiratory compensation
C. Metabolic alkalosis with respiratory compensation
D. Respiratory alkalosis with metabolic compensation
E. Mixed metabolic and respiratory acidosis
1
,Answer: B. Metabolic acidosis with appropriate respiratory
compensation
Rationale: The pH of 7.18 indicates acidemia, while the markedly
decreased HCO₃⁻ of 10 mEq/L identifies a primary metabolic acidosis.
The low PaCO₂ reflects compensatory hyperventilation. Using Winter's
formula, expected PaCO₂ = 1.5(HCO₃⁻) + 8 ± 2 = 1.5(10) + 8 ± 2 = 23
± 2 mm Hg. The measured PaCO₂ of 24 mm Hg is appropriately
compensatory. In this clinical setting, insulin deficiency causes
diabetic ketoacidosis, producing an increased-anion-gap metabolic
acidosis.
Question 2
A 68-year-old man with severe chronic obstructive pulmonary disease
has progressive dyspnea. His arterial blood gas shows:
pH: 7.36
PaCO₂: 60 mm Hg
HCO₃⁻: 33 mEq/L
Which of the following is the most likely interpretation?
A. Acute respiratory acidosis
B. Chronic respiratory acidosis with renal compensation
C. Metabolic alkalosis with respiratory compensation
D. Mixed respiratory acidosis and metabolic acidosis
E. Chronic respiratory alkalosis
Answer: B. Chronic respiratory acidosis with renal compensation
Rationale: The elevated PaCO₂ demonstrates respiratory acidosis.
Because the pH is close to normal and HCO₃⁻ is substantially elevated,
the kidneys have retained bicarbonate to compensate for chronic CO₂
retention. In chronic respiratory acidosis, HCO₃⁻ rises approximately
2
,3.5–4 mEq/L for every 10-mm-Hg increase in PaCO₂ above 40 mm
Hg. A PaCO₂ of 60 would therefore predict an HCO₃⁻ around 31–32
mEq/L, making 33 mEq/L highly compatible with chronic
compensation.
Question 3
A 35-year-old woman is hyperventilating during a severe panic attack.
ABG analysis shows:
pH: 7.52
PaCO₂: 25 mm Hg
HCO₃⁻: 20 mEq/L
Which acid-base disturbance is present?
A. Acute respiratory alkalosis
B. Chronic respiratory alkalosis
C. Metabolic alkalosis
D. Metabolic acidosis
E. Mixed respiratory alkalosis and metabolic alkalosis
Answer: A. Acute respiratory alkalosis
Rationale: The elevated pH establishes alkalemia, and the markedly
reduced PaCO₂ identifies a primary respiratory alkalosis. In acute
respiratory alkalosis, HCO₃⁻ falls approximately 2 mEq/L for every 10-
mm-Hg decrease in PaCO₂. A PaCO₂ decrease from 40 to 25 mm Hg
should therefore decrease HCO₃⁻ by approximately 3 mEq/L,
producing a value near 21 mEq/L. The measured HCO₃⁻ of 20 is
consistent with acute respiratory alkalosis.
Question 4
3
, A 72-year-old woman presents with persistent vomiting for 5 days due
to gastric outlet obstruction. Laboratory studies show:
Na⁺: 140 mEq/L
Cl⁻: 88 mEq/L
HCO₃⁻: 38 mEq/L
K⁺: 2.7 mEq/L
Which acid-base disturbance is most likely present?
A. Increased-anion-gap metabolic acidosis
B. Normal-anion-gap metabolic acidosis
C. Metabolic alkalosis
D. Respiratory alkalosis
E. Respiratory acidosis
Answer: C. Metabolic alkalosis
Rationale: The elevated HCO₃⁻ and history of prolonged vomiting
indicate metabolic alkalosis caused by loss of gastric hydrochloric
acid. Volume depletion activates the renin-angiotensin-aldosterone
system, increasing distal sodium reabsorption and promoting
potassium and hydrogen ion secretion. Hypokalemia further maintains
the alkalosis. The low chloride concentration is characteristic of
chloride-responsive metabolic alkalosis associated with vomiting.
Question 5
A 55-year-old man presents with severe diarrhea for several days.
Laboratory studies demonstrate:
Na⁺: 140 mEq/L
Cl⁻: 115 mEq/L
HCO₃⁻: 15 mEq/L
4
PRACTICE EXAM WITH QUESTIONS AND
VERIFIED ANSWERS, PLUS DETAILED
RATIONALES/EXPERT VERIFIED FOR
GUARANTEED PASS 2026/LATEST
UPDATE/INSTANT DOWNLOAD PDF
Question 1
A 23-year-old woman with type 1 diabetes mellitus presents with
nausea, vomiting, abdominal pain, and progressively increasing lethargy.
She has been unable to obtain insulin for 2 days. Her respiratory rate is
30/min with deep respirations. Laboratory studies show:
Na⁺: 138 mEq/L
Cl⁻: 100 mEq/L
HCO₃⁻: 10 mEq/L
Glucose: 420 mg/dL
Arterial blood gas:
pH: 7.18
PaCO₂: 24 mm Hg
Which of the following best describes this patient's acid-base disorder?
A. Respiratory acidosis with metabolic compensation
B. Metabolic acidosis with appropriate respiratory compensation
C. Metabolic alkalosis with respiratory compensation
D. Respiratory alkalosis with metabolic compensation
E. Mixed metabolic and respiratory acidosis
1
,Answer: B. Metabolic acidosis with appropriate respiratory
compensation
Rationale: The pH of 7.18 indicates acidemia, while the markedly
decreased HCO₃⁻ of 10 mEq/L identifies a primary metabolic acidosis.
The low PaCO₂ reflects compensatory hyperventilation. Using Winter's
formula, expected PaCO₂ = 1.5(HCO₃⁻) + 8 ± 2 = 1.5(10) + 8 ± 2 = 23
± 2 mm Hg. The measured PaCO₂ of 24 mm Hg is appropriately
compensatory. In this clinical setting, insulin deficiency causes
diabetic ketoacidosis, producing an increased-anion-gap metabolic
acidosis.
Question 2
A 68-year-old man with severe chronic obstructive pulmonary disease
has progressive dyspnea. His arterial blood gas shows:
pH: 7.36
PaCO₂: 60 mm Hg
HCO₃⁻: 33 mEq/L
Which of the following is the most likely interpretation?
A. Acute respiratory acidosis
B. Chronic respiratory acidosis with renal compensation
C. Metabolic alkalosis with respiratory compensation
D. Mixed respiratory acidosis and metabolic acidosis
E. Chronic respiratory alkalosis
Answer: B. Chronic respiratory acidosis with renal compensation
Rationale: The elevated PaCO₂ demonstrates respiratory acidosis.
Because the pH is close to normal and HCO₃⁻ is substantially elevated,
the kidneys have retained bicarbonate to compensate for chronic CO₂
retention. In chronic respiratory acidosis, HCO₃⁻ rises approximately
2
,3.5–4 mEq/L for every 10-mm-Hg increase in PaCO₂ above 40 mm
Hg. A PaCO₂ of 60 would therefore predict an HCO₃⁻ around 31–32
mEq/L, making 33 mEq/L highly compatible with chronic
compensation.
Question 3
A 35-year-old woman is hyperventilating during a severe panic attack.
ABG analysis shows:
pH: 7.52
PaCO₂: 25 mm Hg
HCO₃⁻: 20 mEq/L
Which acid-base disturbance is present?
A. Acute respiratory alkalosis
B. Chronic respiratory alkalosis
C. Metabolic alkalosis
D. Metabolic acidosis
E. Mixed respiratory alkalosis and metabolic alkalosis
Answer: A. Acute respiratory alkalosis
Rationale: The elevated pH establishes alkalemia, and the markedly
reduced PaCO₂ identifies a primary respiratory alkalosis. In acute
respiratory alkalosis, HCO₃⁻ falls approximately 2 mEq/L for every 10-
mm-Hg decrease in PaCO₂. A PaCO₂ decrease from 40 to 25 mm Hg
should therefore decrease HCO₃⁻ by approximately 3 mEq/L,
producing a value near 21 mEq/L. The measured HCO₃⁻ of 20 is
consistent with acute respiratory alkalosis.
Question 4
3
, A 72-year-old woman presents with persistent vomiting for 5 days due
to gastric outlet obstruction. Laboratory studies show:
Na⁺: 140 mEq/L
Cl⁻: 88 mEq/L
HCO₃⁻: 38 mEq/L
K⁺: 2.7 mEq/L
Which acid-base disturbance is most likely present?
A. Increased-anion-gap metabolic acidosis
B. Normal-anion-gap metabolic acidosis
C. Metabolic alkalosis
D. Respiratory alkalosis
E. Respiratory acidosis
Answer: C. Metabolic alkalosis
Rationale: The elevated HCO₃⁻ and history of prolonged vomiting
indicate metabolic alkalosis caused by loss of gastric hydrochloric
acid. Volume depletion activates the renin-angiotensin-aldosterone
system, increasing distal sodium reabsorption and promoting
potassium and hydrogen ion secretion. Hypokalemia further maintains
the alkalosis. The low chloride concentration is characteristic of
chloride-responsive metabolic alkalosis associated with vomiting.
Question 5
A 55-year-old man presents with severe diarrhea for several days.
Laboratory studies demonstrate:
Na⁺: 140 mEq/L
Cl⁻: 115 mEq/L
HCO₃⁻: 15 mEq/L
4
