Acid-base balance NCLEX-RN Practice Questions

Acid-base balance NCLEX-RN Practice Questions

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Acid-Base Balance NCLEX-RN Practice Questions help you master high-yield physiology and clinical reasoning needed for safe, effective nursing care. This topic from Physiological Adaptation emphasizes interpreting arterial blood gases (ABGs), identifying primary versus compensatory processes, and selecting correct interventions. You’ll evaluate ventilator settings, understand how conditions like COPD, DKA, sepsis, vomiting, and diarrhea affect pH, and anticipate electrolyte shifts—especially potassium. These 30 NCLEX-style questions focus on realistic clinical vignettes, priority actions, and lab interpretation you’ll encounter in acute care. Use them to sharpen your ability to analyze patterns (pH, PaCO2, HCO3−), differentiate respiratory from metabolic disorders, and implement evidence-based nursing interventions, including oxygenation, ventilation, fluids, and medication therapy.

Q1. A client’s ABG results are: pH 7.30, PaCO2 50 mm Hg, HCO3− 24 mEq/L. Which interpretation is most accurate?

  • Metabolic acidosis
  • Uncompensated respiratory acidosis
  • Partially compensated metabolic alkalosis
  • Fully compensated respiratory acidosis

Correct Answer: Uncompensated respiratory acidosis

Q2. A post-op client is anxious, breathing at 32/min, lightheaded, and has perioral tingling. ABG: pH 7.52, PaCO2 28 mm Hg, HCO3− 24 mEq/L. Priority intervention?

  • Encourage slow, guided breathing and reduce environmental stimuli
  • Administer IV sodium bicarbonate
  • Increase oxygen to non-rebreather 15 L/min
  • Prepare for intubation and mechanical ventilation

Correct Answer: Encourage slow, guided breathing and reduce environmental stimuli

Q3. A patient with DKA presents with Kussmaul respirations. Expected ABG pattern?

  • pH low, PaCO2 high, HCO3− normal
  • pH high, PaCO2 low, HCO3− low
  • pH low, PaCO2 low, HCO3− low
  • pH high, PaCO2 high, HCO3− high

Correct Answer: pH low, PaCO2 low, HCO3− low

Q4. Which finding is most consistent with metabolic alkalosis?

  • Chronic diarrhea with serum K+ 5.8 mEq/L
  • Prolonged vomiting with serum K+ 3.0 mEq/L
  • Sepsis with lactate 6 mmol/L
  • Salicylate overdose presenting late with confusion and PaCO2 55 mm Hg

Correct Answer: Prolonged vomiting with serum K+ 3.0 mEq/L

Q5. A COPD patient on 2 L/min nasal cannula: ABG pH 7.36, PaCO2 55 mm Hg, HCO3− 30 mEq/L. Which is the best interpretation?

  • Uncompensated respiratory acidosis
  • Partially compensated metabolic alkalosis
  • Fully compensated respiratory acidosis
  • Mixed metabolic acidosis and respiratory alkalosis

Correct Answer: Fully compensated respiratory acidosis

Q6. A client with severe diarrhea has pH 7.28, PaCO2 37 mm Hg, HCO3− 17 mEq/L. Priority nursing action?

  • Administer antiemetic and stop NG suction
  • Start isotonic fluids and monitor potassium levels
  • Increase ventilator rate
  • Administer naloxone

Correct Answer: Start isotonic fluids and monitor potassium levels

Q7. For a patient on mechanical ventilation with respiratory alkalosis, which ventilator adjustment is most appropriate?

  • Increase tidal volume
  • Increase respiratory rate
  • Decrease respiratory rate
  • Increase FiO2

Correct Answer: Decrease respiratory rate

Q8. A client with salicylate overdose arrives early after ingestion. Which acid-base disorder is most likely initially?

  • Respiratory alkalosis
  • Respiratory acidosis
  • Metabolic alkalosis
  • Metabolic acidosis with high anion gap

Correct Answer: Respiratory alkalosis

Q9. Which arterial blood gas is consistent with metabolic alkalosis with partial respiratory compensation?

  • pH 7.48, PaCO2 48 mm Hg, HCO3− 34 mEq/L
  • pH 7.30, PaCO2 50 mm Hg, HCO3− 24 mEq/L
  • pH 7.36, PaCO2 60 mm Hg, HCO3− 33 mEq/L
  • pH 7.25, PaCO2 25 mm Hg, HCO3− 11 mEq/L

Correct Answer: pH 7.48, PaCO2 48 mm Hg, HCO3− 34 mEq/L

Q10. A patient with oliguric acute kidney injury has ABG: pH 7.22, PaCO2 30 mm Hg, HCO3− 12 mEq/L. Which mechanism explains the PaCO2?

  • Primary respiratory alkalosis
  • Compensatory hyperventilation for metabolic acidosis
  • Compensatory hypoventilation for metabolic acidosis
  • Primary respiratory acidosis

Correct Answer: Compensatory hyperventilation for metabolic acidosis

Q11. Which client is at greatest risk for developing contraction metabolic alkalosis?

  • Client with prolonged loop diuretic therapy and low urine chloride
  • Client on metformin with lactic acidosis
  • Client with severe COPD exacerbation
  • Client with profuse diarrhea

Correct Answer: Client with prolonged loop diuretic therapy and low urine chloride

Q12. A patient receiving morphine PCA becomes somnolent, RR 6/min, pinpoint pupils. ABG: pH 7.26, PaCO2 60 mm Hg, HCO3− 24 mEq/L. Priority action?

  • Administer naloxone per protocol
  • Administer sodium bicarbonate IV push
  • Encourage pursed-lip breathing
  • Start hypotonic fluids

Correct Answer: Administer naloxone per protocol

Q13. A client with severe vomiting and NG suction has: pH 7.49, PaCO2 46 mm Hg, HCO3− 34 mEq/L. Best nursing action?

  • Increase suction pressure
  • Administer 0.9% saline with potassium chloride as prescribed
  • Restrict fluids and start loop diuretics
  • Prepare to administer sodium bicarbonate

Correct Answer: Administer 0.9% saline with potassium chloride as prescribed

Q14. Which ABG indicates a mixed acid-base disorder rather than full compensation?

  • pH 7.40, PaCO2 60 mm Hg, HCO3− 36 mEq/L
  • pH 7.35, PaCO2 55 mm Hg, HCO3− 30 mEq/L
  • pH 7.50, PaCO2 30 mm Hg, HCO3− 24 mEq/L
  • pH 7.32, PaCO2 60 mm Hg, HCO3− 30 mEq/L

Correct Answer: pH 7.32, PaCO2 60 mm Hg, HCO3− 30 mEq/L

Q15. A septic patient on vasopressors has lactate 6 mmol/L. Which ABG is most consistent?

  • pH 7.55, PaCO2 28 mm Hg, HCO3− 24 mEq/L
  • pH 7.28, PaCO2 30 mm Hg, HCO3− 14 mEq/L
  • pH 7.36, PaCO2 55 mm Hg, HCO3− 30 mEq/L
  • pH 7.48, PaCO2 48 mm Hg, HCO3− 34 mEq/L

Correct Answer: pH 7.28, PaCO2 30 mm Hg, HCO3− 14 mEq/L

Q16. A patient with panic attack is hyperventilating. What electrolyte change is most likely?

  • Hyperkalemia due to extracellular shift
  • Hypokalemia due to intracellular shift
  • Hypercalcemia due to albumin binding changes
  • Hypermagnesemia from renal retention

Correct Answer: Hypokalemia due to intracellular shift

Q17. Which assessment finding supports metabolic acidosis due to diarrhea rather than DKA?

  • Elevated anion gap with fruity breath
  • Normal anion gap with hyperchloremia
  • Marked ketonuria and hyperglycemia
  • Kussmaul respirations with serum ketones positive

Correct Answer: Normal anion gap with hyperchloremia

Q18. ABG: pH 7.44, PaCO2 30 mm Hg, HCO3− 20 mEq/L. Interpretation?

  • Metabolic acidosis fully compensated by respiratory alkalosis
  • Primary respiratory alkalosis with metabolic compensation
  • Uncompensated metabolic acidosis
  • Mixed metabolic acidosis and respiratory alkalosis with alkalemia

Correct Answer: Primary respiratory alkalosis with metabolic compensation

Q19. A malnourished alcoholic with starvation ketoacidosis is started on dextrose-containing fluids and insulin. Which electrolyte change requires the most vigilant monitoring?

  • Hypernatremia
  • Hypokalemia
  • Hyperchloremia
  • Hypercalcemia

Correct Answer: Hypokalemia

Q20. For a patient with metabolic alkalosis from NG suction, which order would the nurse question?

  • Acetazolamide IV for persistent alkalosis
  • Decrease suction and use intermittent low wall suction
  • 0.45% saline at 150 mL/hr
  • Potassium chloride supplementation

Correct Answer: 0.45% saline at 150 mL/hr

Q21. A patient with status asthmaticus is tiring: RR falls from 34 to 16, accessory muscle use decreases, but mental status worsens. ABG now shows rising PaCO2 and falling pH. Priority action?

  • Continue current therapy and observe
  • Administer sodium bicarbonate
  • Prepare for intubation and mechanical ventilation
  • Restrict fluids and start diuretics

Correct Answer: Prepare for intubation and mechanical ventilation

Q22. Which intervention most directly corrects respiratory acidosis from hypoventilation?

  • Administer IV bicarbonate
  • Improve ventilation by addressing airway and respiratory drive
  • Restrict chloride intake
  • Administer lactated Ringer’s bolus

Correct Answer: Improve ventilation by addressing airway and respiratory drive

Q23. A client with advanced COPD has chronic CO2 retention. Which oxygen strategy minimizes risk of CO2 narcosis while maintaining adequate oxygenation?

  • High-flow non-rebreather at 15 L/min to achieve SpO2 100%
  • Titrate oxygen to maintain SpO2 88–92%
  • Keep patient on room air unless PaO2 < 50 mm Hg
  • Use 100% FiO2 via Venturi mask continuously

Correct Answer: Titrate oxygen to maintain SpO2 88–92%

Q24. Which ABG pattern suggests a mixed metabolic acidosis and respiratory alkalosis (e.g., sepsis with hyperventilation)?

  • pH 7.20, PaCO2 60 mm Hg, HCO3− 23 mEq/L
  • pH 7.50, PaCO2 50 mm Hg, HCO3− 36 mEq/L
  • pH 7.38, PaCO2 40 mm Hg, HCO3− 24 mEq/L
  • pH 7.36, PaCO2 28 mm Hg, HCO3− 15 mEq/L

Correct Answer: pH 7.36, PaCO2 28 mm Hg, HCO3− 15 mEq/L

Q25. A patient with severe metabolic acidosis (pH 7.10) is being considered for bicarbonate therapy. Which condition most supports cautious bicarbonate use?

  • DKA with responsive perfusion
  • Lactic acidosis from sepsis with ongoing hypoperfusion
  • Life-threatening hyperkalemia with EKG changes
  • Chronic respiratory acidosis

Correct Answer: Life-threatening hyperkalemia with EKG changes

Q26. After a large transfusion with citrated blood, a patient develops tetany and perioral numbness. Which acid-base/electrolyte association is most likely?

  • Alkalosis increasing protein-bound calcium, causing symptoms
  • Acidosis increasing ionized calcium, causing tetany
  • Hyperkalemia causing neuromuscular irritability
  • Hypermagnesemia causing paresthesias

Correct Answer: Alkalosis increasing protein-bound calcium, causing symptoms

Q27. A patient has: Na+ 140 mEq/L, Cl− 110 mEq/L, HCO3− 14 mEq/L. What is the anion gap and likely etiology?

  • Anion gap 16; lactic acidosis
  • Anion gap 12; normal gap acidosis from diarrhea
  • Anion gap 6; normal gap acidosis from diarrhea
  • Anion gap 20; ketoacidosis

Correct Answer: Anion gap 16; lactic acidosis

Q28. A cirrhotic patient is hyperventilating because of hepatic encephalopathy. ABG: pH 7.50, PaCO2 30 mm Hg, HCO3− 23 mEq/L. Which nursing intervention addresses the cause?

  • Prepare lactulose administration to reduce ammonia
  • Administer sodium bicarbonate
  • Start diuretics to reduce ascites immediately
  • Increase dietary protein

Correct Answer: Prepare lactulose administration to reduce ammonia

Q29. A client with severe metabolic alkalosis (pH 7.56) from diuretics is hypotensive and hypokalemic. Best initial fluid choice?

  • 0.9% normal saline with potassium chloride
  • 0.45% saline without potassium
  • D5W alone
  • 3% hypertonic saline

Correct Answer: 0.9% normal saline with potassium chloride

Q30. A patient with myasthenia gravis develops impending respiratory failure: ABG shows rising PaCO2 and decreasing pH with normal HCO3−. What is the primary disorder and priority?

  • Metabolic acidosis; administer bicarbonate
  • Respiratory acidosis; support ventilation
  • Metabolic alkalosis; stop NG suction
  • Respiratory alkalosis; provide paper bag breathing

Correct Answer: Respiratory acidosis; support ventilation

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