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ABG Interpretation NCLEX practice questions
Arterial blood gas questions come down to three numbers (pH, PaCO2, HCO3) and the pattern they make. Practice naming the imbalance, then the cause and the nursing action, which is how the NCLEX asks it.
Question 1 · Physiological Adaptation
A client who received an opioid overdose has the following ABG: pH 7.28, PaCO2 58 mmHg, HCO3 24 mEq/L. Which acid-base imbalance is present?
Show answer and rationale
Answer: B. Opioids depress the respiratory drive, causing hypoventilation, CO2 retention, and a resulting respiratory acidosis, shown here by the low pH and elevated CO2 with a normal HCO3. Metabolic acidosis would show a low HCO3, which is not present. Respiratory alkalosis and metabolic alkalosis both require a high pH, which contradicts this ABG. This pattern is the classic ABG picture for opioid-induced hypoventilation.
Checked against: OpenStax Medical-Surgical Nursing, 10.4
Question 2 · Reduction of Risk Potential
A nurse is reviewing the history of a client diagnosed with metabolic alkalosis. Which conditions are consistent with this diagnosis? Select all that apply.
Select all that apply.
Show answer and rationale
Answer: B, C, F. Prolonged vomiting, nasogastric suctioning, and excessive antacid use all cause loss of gastric acid or excess intake of base, raising the pH and HCO3 to produce metabolic alkalosis. Diarrhea causes loss of bicarbonate-rich intestinal fluid, which leads to metabolic acidosis, not alkalosis. Diabetic ketoacidosis produces metabolic acidosis from ketone accumulation, and opioid overdose produces respiratory acidosis from hypoventilation, so neither is associated with metabolic alkalosis.
Checked against: OpenStax Medical-Surgical Nursing, 10.4
Question 3 · Physiological Adaptation
An ABG shows pH 7.48, PaCO2 30 mmHg, HCO3 20 mEq/L. What does this indicate?
Show answer and rationale
Answer: D. The elevated pH of 7.48 indicates alkalosis, and the low PaCO2 of 30 mmHg (opposite direction) points to a respiratory cause. The HCO3 of 20 mEq/L is now below normal, showing the kidneys are excreting bicarbonate to try to bring the pH down, but since the pH remains above 7.45, compensation is only partial. Uncompensated is incorrect because HCO3 has already shifted, and fully compensated is wrong because the pH is still outside normal limits. Metabolic acidosis is incorrect since the primary problem, based on the CO2 direction, is respiratory.
Checked against: OpenStax Medical-Surgical Nursing, 10.4
Question 4 · Physiological Adaptation
A client's ABG results are pH 7.36, PaCO2 50 mmHg, HCO3 29 mEq/L. Which interpretation is correct?
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Answer: C. The pH of 7.36 is within normal limits but on the acidic side (below 7.40), suggesting the original problem was an acidosis. Both the PaCO2 (50 mmHg, high) and HCO3 (29 mEq/L, high) are abnormal, showing the kidneys have compensated for the respiratory problem by retaining bicarbonate until the pH normalized. This makes it fully, not partially, compensated because the pH is back in the normal range. Uncompensated is wrong because compensation clearly occurred, and metabolic alkalosis is incorrect since the primary disturbance direction (CO2 opposite pH) is respiratory.
Checked against: OpenStax Fundamentals of Nursing, 20.3; OpenStax Medical-Surgical Nursing, 10.4
Question 5 · Physiological Adaptation
An ABG shows pH 7.52, PaCO2 40 mmHg, HCO3 30 mEq/L. How should the nurse classify this result?
Show answer and rationale
Answer: A. The elevated pH of 7.52 indicates alkalosis, and the HCO3 of 30 mEq/L is high in the same direction, per ROME's 'Metabolic Equal' rule, pointing to a metabolic cause. The PaCO2 of 40 mmHg is normal, showing the lungs have not compensated, so this is uncompensated. Respiratory alkalosis is incorrect since PaCO2 is not low. Compensated classifications require an abnormal PaCO2, which is absent in this result.
Checked against: OpenStax Medical-Surgical Nursing, 10.4
Question 6 · Physiological Adaptation
Which client situations would place a client at risk for metabolic alkalosis? Select all that apply.
Select all that apply.
Show answer and rationale
Answer: A, C, D, E. Metabolic alkalosis results from loss of acid or gain of base, such as prolonged vomiting, NG suction (both remove stomach acid), excessive antacid intake, and diuretic-induced electrolyte losses. Severe diarrhea causes loss of bicarbonate and leads to metabolic acidosis instead, so it does not belong on this list. Opioid overdose causes hypoventilation and respiratory acidosis, which is unrelated to the metabolic alkalosis mechanism described here.
Checked against: OpenStax Medical-Surgical Nursing, 10.4
Question 7 · Physiological Adaptation
An ABG shows pH 7.36, PaCO2 50 mmHg, and HCO3 29 mEq/L. How should the nurse interpret this result?
Show answer and rationale
Answer: B. The pH is within normal limits but on the acidic side of 7.40, while both CO2 and HCO3 are abnormal (elevated), indicating the kidneys have compensated for a primary respiratory acidosis by retaining bicarbonate. It is not uncompensated because the pH has returned to a near-normal value. It is not metabolic alkalosis because the pH sits on the acid side of 7.40, identifying the original problem as acidosis, not alkalosis, despite the elevated HCO3.
Checked against: OpenStax Medical-Surgical Nursing, 10.4
Question 8 · Pharmacological and Parenteral Therapies
A nurse is caring for a client who received a large dose of intravenous morphine and now has shallow respirations at a rate of 6 breaths/min. Which acid-base imbalance should the nurse expect on ABG analysis?
Show answer and rationale
Answer: D. Opioids depress the respiratory drive, causing hypoventilation and CO2 retention, which leads to respiratory acidosis. Respiratory alkalosis would occur with hyperventilation, which is the opposite problem. Metabolic acidosis and metabolic alkalosis involve primary changes in bicarbonate from renal, gastrointestinal, or metabolic causes, not from a change in ventilation. The priority nursing actions are to administer naloxone as prescribed and support the client's airway and breathing.
Checked against: OpenStax Fundamentals of Nursing, 20.3; OpenStax Medical-Surgical Nursing, 10.4
Question 9 · Physiological Adaptation
A client's ABG results are pH 7.33, PaCO2 28 mmHg, HCO3 15 mEq/L. How should the nurse interpret this?
Show answer and rationale
Answer: A. The low pH of 7.33 indicates acidosis, and the low HCO3 of 15 mEq/L moves in the same direction, per ROME's metabolic rule, showing a metabolic cause. The PaCO2 of 28 mmHg is low, showing the lungs are compensating by hyperventilating to blow off CO2, but the pH has not yet normalized, so compensation is partial. Uncompensated is wrong because the PaCO2 has already changed in response, and fully compensated is wrong because the pH remains outside the normal range. Respiratory acidosis is incorrect since the direction of the primary abnormality (HCO3 matching pH) points to a metabolic problem.
Checked against: OpenStax Medical-Surgical Nursing, 10.4
Question 10 · Physiological Adaptation
A client's ABG results are pH 7.30, PaCO2 40 mmHg, HCO3 18 mEq/L. Which interpretation is correct?
Show answer and rationale
Answer: A. The pH of 7.30 shows acidosis, and per ROME (Metabolic Equal), the HCO3 of 18 mEq/L is low in the same direction as the low pH, identifying a metabolic cause. The PaCO2 of 40 mmHg is exactly normal, meaning the lungs have not begun to compensate by blowing off CO2, so this is uncompensated. Respiratory acidosis is wrong because PaCO2 is normal, not elevated. Partial or full compensation would require an abnormal PaCO2, which is not present here.
Checked against: OpenStax Medical-Surgical Nursing, 10.4; OpenStax Fundamentals of Nursing, 20.3
Question 11 · Physiological Adaptation
The nurse enters the room of a client with COPD and notes the client has become increasingly drowsy over the past hour. What should the nurse suspect first?
Show answer and rationale
Answer: D. In a client with COPD, increasing drowsiness or somnolence is a hallmark sign of CO2 narcosis from worsening respiratory acidosis, and the nurse should obtain an ABG promptly before administering any sedating medications. Hypoglycemia can cause altered mental status but is not the priority suspicion in a COPD client with a known risk for CO2 retention. Hyperventilation would cause increased alertness or anxiety, not drowsiness, and would not fit this pattern. Metabolic alkalosis from diuretics does not typically present with progressive somnolence in this context.
Checked against: OpenStax Medical-Surgical Nursing, 10.4
Question 12 · Physiological Adaptation
A nurse reviews an ABG result showing a pH of 7.31. According to the stepwise approach to acid-base analysis, what should the nurse determine first, before looking at the CO2 or HCO3 values?
Show answer and rationale
Answer: D. The first step in acid-base analysis is always to look at the pH alone: below 7.35 means acidosis, above 7.45 means alkalosis. Only after naming the general problem does the nurse compare CO2 and HCO3 to determine whether the cause is respiratory or metabolic. Naming it as respiratory or metabolic acidosis at this point is premature because those values have not yet been reviewed. Assuming compensation is also premature since compensation status requires comparing all three values.
Checked against: OpenStax Medical-Surgical Nursing, 10.4
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Frequently asked questions
How do you interpret an ABG for the NCLEX?
Check the pH first (acidosis or alkalosis), then see whether PaCO2 (respiratory) or HCO3 (metabolic) explains it, then check whether the other value is compensating. The ABG cheat sheet and video below walk through it.
Review first
About these questions
Every question on this page was approved by a licensed RN, and its answer was checked against open nursing references (mostly OpenStax nursing textbooks) before publishing. They are NCLEX-style practice, not real NCLEX items. NurseLingo is not affiliated with NCSBN. Spot a problem? Tell us.