🎯 High-Yield Points
- pH <7.35 = acidosis; pH >7.45 = alkalosis
- CO2 is respiratory: high CO2 = respiratory acidosis; low CO2 = respiratory alkalosis
- HCO3 is metabolic: low HCO3 = metabolic acidosis; high HCO3 = metabolic alkalosis
- ROME: Respiratory Opposite, Metabolic Equal (pH and CO2/HCO3 direction)
- DKA causes metabolic acidosis; hyperventilation causes respiratory alkalosis
[Concept Map: Acid-Base Balance NCLEX Questions — Clinical Manifestations, Nursing Interventions, Priority Actions]
Practice Questions
Question 1
A client's ABG results show: pH 7.28, PaCO2 58 mmHg, HCO3 24 mEq/L. Which interpretation is correct?
✓ Correct: Respiratory acidosis, uncompensated
Interpretation: pH 7.28 = acidosis. CO2 58 = elevated = respiratory problem (causes acidosis). HCO3 24 = normal (no compensation has occurred). Conclusion: Respiratory acidosis, uncompensated. The respiratory system is the cause; the metabolic system has not yet compensated by retaining HCO3. Causes: COPD exacerbation, respiratory depression, pneumonia. Treatment: improve ventilation, possibly mechanical ventilation.
Interpretation: pH 7.28 = acidosis. CO2 58 = elevated = respiratory problem (causes acidosis). HCO3 24 = normal (no compensation has occurred). Conclusion: Respiratory acidosis, uncompensated. The respiratory system is the cause; the metabolic system has not yet compensated by retaining HCO3. Causes: COPD exacerbation, respiratory depression, pneumonia. Treatment: improve ventilation, possibly mechanical ventilation.
Question 2
A client experiencing severe anxiety hyperventilates. Which ABG change is expected?
✓ Correct: Increased pH, decreased CO2
Hyperventilation blows off CO2 (decreases PaCO2), which reduces carbonic acid in the blood, raising pH. Result: Respiratory alkalosis — elevated pH, low CO2. Symptoms include tingling, dizziness, carpopedal spasm. Treatment: help client breathe into a paper bag to rebreathe CO2, or coach slow deep breathing. Teaching: breathe slowly and deeply, not rapidly and shallowly.
Hyperventilation blows off CO2 (decreases PaCO2), which reduces carbonic acid in the blood, raising pH. Result: Respiratory alkalosis — elevated pH, low CO2. Symptoms include tingling, dizziness, carpopedal spasm. Treatment: help client breathe into a paper bag to rebreathe CO2, or coach slow deep breathing. Teaching: breathe slowly and deeply, not rapidly and shallowly.
Question 3
A client with chronic diarrhoea has: pH 7.31, PaCO2 36 mmHg, HCO3 16 mEq/L. Which interpretation is correct?
✓ Correct: Metabolic acidosis, uncompensated
pH 7.31 = acidosis. CO2 36 = normal (respiratory is not the cause). HCO3 16 = low = metabolic problem causing acidosis. No compensation (CO2 is still normal). Conclusion: Metabolic acidosis, uncompensated. Causes: severe diarrhoea (loss of HCO3 in stool), DKA, renal failure, lactic acidosis. The respiratory system will compensate by increasing ventilation (lowering CO2) — this is called Kussmaul breathing when severe.
pH 7.31 = acidosis. CO2 36 = normal (respiratory is not the cause). HCO3 16 = low = metabolic problem causing acidosis. No compensation (CO2 is still normal). Conclusion: Metabolic acidosis, uncompensated. Causes: severe diarrhoea (loss of HCO3 in stool), DKA, renal failure, lactic acidosis. The respiratory system will compensate by increasing ventilation (lowering CO2) — this is called Kussmaul breathing when severe.
Question 4
A client post-nasogastric suctioning has: pH 7.51, PaCO2 42 mmHg, HCO3 32 mEq/L. Which interpretation is correct?
✓ Correct: Metabolic alkalosis, uncompensated
pH 7.51 = alkalosis. CO2 42 = normal (respiratory is not the cause). HCO3 32 = elevated = metabolic problem causing alkalosis. No compensation. Conclusion: Metabolic alkalosis, uncompensated. Causes: prolonged NG suctioning removes HCl (hydrochloric acid), loss of vomiting, excessive antacid use, or diuresis causing HCO3 retention. Treatment: replace electrolytes (especially potassium and chloride), address the cause.
pH 7.51 = alkalosis. CO2 42 = normal (respiratory is not the cause). HCO3 32 = elevated = metabolic problem causing alkalosis. No compensation. Conclusion: Metabolic alkalosis, uncompensated. Causes: prolonged NG suctioning removes HCl (hydrochloric acid), loss of vomiting, excessive antacid use, or diuresis causing HCO3 retention. Treatment: replace electrolytes (especially potassium and chloride), address the cause.
Question 5
A nurse is caring for a client on a ventilator. The ventilator rate is decreased. Which ABG change does the nurse anticipate?
✓ Correct: Increased CO2 and decreased pH
Decreasing the ventilator respiratory rate reduces the frequency of breaths, causing CO2 to accumulate (less CO2 being blown off). Increased CO2 creates carbonic acid, lowering pH. Result: Respiratory acidosis (CO2 increases, pH decreases). The nurse must monitor ABGs after ventilator adjustments and communicate findings to the respiratory therapist and provider. This is why ventilator settings require careful titration.
Decreasing the ventilator respiratory rate reduces the frequency of breaths, causing CO2 to accumulate (less CO2 being blown off). Increased CO2 creates carbonic acid, lowering pH. Result: Respiratory acidosis (CO2 increases, pH decreases). The nurse must monitor ABGs after ventilator adjustments and communicate findings to the respiratory therapist and provider. This is why ventilator settings require careful titration.
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