Arterial Blood Gas Interpretation for NCLEX Practice Quiz
Basics of ABG Interpretation
- Q: What is the normal range for pH in an arterial blood gas?
A: 7.35 – 7.45 - Q: What is the normal range for PaCO₂?
A: 35 – 45 mmHg - Q: What is the normal range for HCO₃⁻ (bicarbonate)?
A: 22 – 26 mEq/L - Q: What is the normal range for PaO₂?
A: 80 – 100 mmHg - Q: What is the normal range for oxygen saturation (SaO₂)?
A: 95 – 100% - Q: What is the term for a pH below 7.35?
A: Acidosis - Q: What is the term for a pH above 7.45?
A: Alkalosis - Q: What does PaCO₂ primarily reflect?
A: Respiratory function - Q: What does HCO₃⁻ primarily reflect?
A: Metabolic function - Q: Which organ regulates bicarbonate levels?
A: Kidneys
Acidosis and Alkalosis Types
- Q: What condition is indicated by pH < 7.35 and PaCO₂ > 45 mmHg?
A: Respiratory acidosis - Q: What condition is indicated by pH > 7.45 and PaCO₂ < 35 mmHg?
A: Respiratory alkalosis - Q: What condition is indicated by pH < 7.35 and HCO₃⁻ < 22 mEq/L?
A: Metabolic acidosis - Q: What condition is indicated by pH > 7.45 and HCO₃⁻ > 26 mEq/L?
A: Metabolic alkalosis - Q: Which acid-base disturbance is most likely in a patient with severe diarrhea?
A: Metabolic acidosis - Q: Which acid-base disturbance is most likely in a patient with prolonged vomiting?
A: Metabolic alkalosis - Q: What is the primary compensatory mechanism for metabolic acidosis?
A: Increased respiratory rate to decrease PaCO₂ - Q: What is the primary compensatory mechanism for respiratory acidosis?
A: Increased renal retention of bicarbonate - Q: What does a normal pH with abnormal PaCO₂ and HCO₃⁻ indicate?
A: Full compensation - Q: Which acid-base disturbance is common in hyperventilation due to anxiety?
A: Respiratory alkalosis
Advanced ABG Scenarios
- Q: A patient has pH 7.32, PaCO₂ 50 mmHg, and HCO₃⁻ 24 mEq/L. What is the interpretation?
A: Respiratory acidosis - Q: A patient has pH 7.48, PaCO₂ 30 mmHg, and HCO₃⁻ 23 mEq/L. What is the interpretation?
A: Respiratory alkalosis - Q: A patient has pH 7.28, PaCO₂ 38 mmHg, and HCO₃⁻ 18 mEq/L. What is the interpretation?
A: Metabolic acidosis - Q: A patient has pH 7.50, PaCO₂ 40 mmHg, and HCO₃⁻ 30 mEq/L. What is the interpretation?
A: Metabolic alkalosis - Q: A patient has pH 7.35, PaCO₂ 50 mmHg, and HCO₃⁻ 30 mEq/L. What is the interpretation?
A: Fully compensated respiratory acidosis
Mixed Acid-Base Disorders
- Q: A patient has pH 7.20, PaCO₂ 50 mmHg, and HCO₃⁻ 18 mEq/L. What is the interpretation?
A: Mixed respiratory and metabolic acidosis. - Q: What is indicated by pH 7.45, PaCO₂ 25 mmHg, and HCO₃⁻ 18 mEq/L?
A: Mixed respiratory alkalosis and metabolic acidosis. - Q: Can full compensation occur in a mixed acid-base disorder?
A: No, full compensation is not possible in mixed disorders.
Common Clinical Scenarios
- Q: A patient with COPD presents with pH 7.36, PaCO₂ 55 mmHg, and HCO₃⁻ 30 mEq/L. What is the likely diagnosis?
A: Compensated respiratory acidosis. - Q: What acid-base disturbance is associated with diabetic ketoacidosis?
A: Metabolic acidosis. - Q: What acid-base disturbance is common in patients with renal failure?
A: Metabolic acidosis. - Q: A patient on mechanical ventilation has pH 7.52, PaCO₂ 25 mmHg, and HCO₃⁻ 24 mEq/L. What is the interpretation?
A: Respiratory alkalosis. - Q: A postoperative patient receiving excessive sodium bicarbonate develops pH 7.60, PaCO₂ 40 mmHg, and HCO₃⁻ 40 mEq/L. What is the interpretation?
A: Metabolic alkalosis. - Q: What acid-base disturbance is common in aspirin overdose?
A: Mixed respiratory alkalosis and metabolic acidosis. - Q: What acid-base disturbance is common in sepsis?
A: Metabolic acidosis due to lactic acidosis. - Q: What acid-base disturbance is expected in a patient with hypoventilation?
A: Respiratory acidosis.
Oxygenation Questions
- Q: What does a PaO₂ of less than 60 mmHg indicate?
A: Hypoxemia. - Q: What does a PaO₂ of more than 100 mmHg indicate?
A: Hyperoxemia. - Q: What is the normal alveolar-arterial (A-a) gradient for a healthy young adult?
A: Less than 15 mmHg. - Q: What oxygenation parameter is most affected in carbon monoxide poisoning?
A: SaO₂ (oxygen saturation). - Q: What oxygen delivery device is used for a PaO₂ below 60 mmHg on room air?
A: Non-rebreather mask or mechanical ventilation. - Q: What does a high A-a gradient suggest?
A: Impaired oxygen diffusion, ventilation-perfusion mismatch, or shunt.
Compensation Mechanisms
- Q: How long does renal compensation for respiratory acidosis take?
A: 24-48 hours. - Q: How does the body compensate for metabolic alkalosis?
A: Hypoventilation to retain CO₂. - Q: What indicates partial compensation in ABG results?
A: Abnormal pH, with one parameter compensating. - Q: What indicates no compensation in ABG results?
A: Abnormal pH with no change in the compensating parameter.
Advanced ABG Calculations
- Q: How do you calculate anion gap?
A: Na⁺ – (Cl⁻ + HCO₃⁻). - Q: What is the normal anion gap range?
A: 8-12 mEq/L. - Q: What conditions cause a high anion gap metabolic acidosis?
A: Ketoacidosis, lactic acidosis, renal failure, or toxin ingestion (MUDPILES mnemonic). - Q: What conditions cause a normal anion gap metabolic acidosis?
A: Diarrhea, renal tubular acidosis, or saline infusion. - Q: How do you calculate expected PaCO₂ in metabolic acidosis (using Winter’s formula)?
A: Expected PaCO₂ = (1.5 × HCO₃⁻) + 8 ± 2. - Q: How do you calculate expected HCO₃⁻ in chronic respiratory acidosis?
A: HCO₃⁻ increases by 4 mEq/L for every 10 mmHg rise in PaCO₂ above 40 mmHg. - Q: What does a higher-than-expected PaCO₂ in metabolic acidosis indicate?
A: Co-existing respiratory acidosis. - Q: What does a lower-than-expected PaCO₂ in metabolic acidosis indicate?
A: Co-existing respiratory alkalosis.
Clinical Practice Scenarios
- Q: A patient has pH 7.40, PaCO₂ 28 mmHg, and HCO₃⁻ 18 mEq/L. What is the interpretation?
A: Fully compensated respiratory alkalosis. - Q: A trauma patient has pH 7.20, PaCO₂ 25 mmHg, and HCO₃⁻ 18 mEq/L. What is the interpretation?
A: Mixed metabolic and respiratory acidosis. - Q: In what scenario might you see pH 7.60, PaCO₂ 48 mmHg, and HCO₃⁻ 44 mEq/L?
A: Metabolic alkalosis with partial respiratory compensation. - Q: What acid-base disorder is suggested by low pH, high PaCO₂, and high HCO₃⁻?
A: Partially compensated respiratory acidosis. - Q: What acid-base disorder is suggested by high pH, low PaCO₂, and low HCO₃⁻?
A: Partially compensated respiratory alkalosis. - Q: A patient with ARDS has pH 7.28, PaCO₂ 48 mmHg, and PaO₂ 55 mmHg on 50% FiO₂. What is the diagnosis?
A: Respiratory acidosis with hypoxemia.
Advanced Compensation and ABG Analysis
- Q: A patient with metabolic acidosis has HCO₃⁻ 14 mEq/L. Using Winter’s formula, calculate the expected PaCO₂.
A: Expected PaCO₂ = (1.5 × 14) + 8 ± 2 = 29 ± 2 mmHg. - Q: A patient has chronic respiratory acidosis with PaCO₂ 60 mmHg. What is the expected HCO₃⁻ if fully compensated?
A: For every 10 mmHg increase in PaCO₂, HCO₃⁻ increases by 4 mEq/L.
Expected HCO₃⁻ = 24 + (4 × 2) = 32 mEq/L. - Q: A patient has pH 7.25, PaCO₂ 50 mmHg, and HCO₃⁻ 22 mEq/L. What is the likely compensation status?
A: Partially compensated respiratory acidosis, as pH is still abnormal. - Q: A patient has metabolic alkalosis with HCO₃⁻ 36 mEq/L. What is the expected PaCO₂ if compensation occurs?
A: Expected PaCO₂ = (0.7 × 36) + 20 ± 5 = 45.2 ± 5 mmHg. - Q: A patient with acute respiratory alkalosis has PaCO₂ 25 mmHg. What is the expected HCO₃⁻?
A: HCO₃⁻ decreases by 2 mEq/L for every 10 mmHg drop in PaCO₂ below 40 mmHg.
Expected HCO₃⁻ = 24 – 3 = 21 mEq/L.
Clinical Case Studies
Case 1: Postoperative Hypoventilation
- Q: A patient post-surgery presents with pH 7.28, PaCO₂ 55 mmHg, and HCO₃⁻ 26 mEq/L. What is the interpretation?
A: Respiratory acidosis with no compensation. - Q: What is the treatment priority in the above case?
A: Address hypoventilation by optimizing respiratory support (e.g., CPAP or mechanical ventilation).
Case 2: Diabetic Ketoacidosis (DKA)
- Q: A patient in DKA has pH 7.10, PaCO₂ 20 mmHg, and HCO₃⁻ 8 mEq/L. What is the interpretation?
A: Metabolic acidosis with partial respiratory compensation. - Q: What lab test can confirm the underlying cause?
A: Serum ketone levels. - Q: What is the primary treatment for the above case?
A: IV insulin and fluid replacement to correct acidosis.
Case 3: Panic Attack
- Q: A patient has pH 7.55, PaCO₂ 28 mmHg, and HCO₃⁻ 23 mEq/L after a panic attack. What is the interpretation?
A: Respiratory alkalosis with no compensation. - Q: What is the recommended management?
A: Reassurance and coaching in breathing techniques (e.g., breathing into a paper bag).
Case 4: Renal Failure
- Q: A patient with chronic kidney disease has pH 7.30, PaCO₂ 40 mmHg, and HCO₃⁻ 18 mEq/L. What is the interpretation?
A: Metabolic acidosis with no compensation. - Q: What is the priority treatment?
A: Correct metabolic acidosis with sodium bicarbonate and manage underlying kidney disease.
Case 5: Mixed Disorder
- Q: A trauma patient has pH 7.15, PaCO₂ 55 mmHg, and HCO₃⁻ 16 mEq/L. What is the interpretation?
A: Mixed respiratory and metabolic acidosis. - Q: What interventions are necessary?
A: Address hypoventilation (e.g., intubation) and manage the metabolic component (e.g., fluid resuscitation or treating sepsis).
Special Clinical Scenarios
- Q: What acid-base disturbance is common during a blood transfusion reaction?
A: Metabolic acidosis. - Q: What acid-base disturbance is seen in pregnancy?
A: Mild respiratory alkalosis due to increased minute ventilation. - Q: What acid-base imbalance is likely with overdose of opioids?
A: Respiratory acidosis. - Q: What is the typical ABG in a patient with ARDS on high ventilator settings?
A: Mixed respiratory acidosis and hypoxemia.
Compensation Review Questions
- Q: What compensates first: lungs or kidneys?
A: Lungs, as respiratory compensation is faster. - Q: Why does metabolic compensation take longer?
A: Renal processes, like bicarbonate retention, require 24-48 hours. - Q: How can you confirm that compensation is appropriate?
A: By checking if PaCO₂ or HCO₃⁻ matches the expected compensation formula.
True/False Practice
- Q: In respiratory acidosis, renal compensation begins immediately.
A: False (it takes 24-48 hours). - Q: In metabolic alkalosis, hypoventilation fully normalizes the pH.
A: False (hypoventilation is limited due to hypoxia risk). - Q: A normal PaCO₂ excludes a respiratory component in mixed disorders.
A: False. - Q: Hypoxia can occur with a normal PaO₂ if hemoglobin is low.
A: True.
Case 6: High-Altitude Sickness
- Q: A mountaineer has pH 7.48, PaCO₂ 28 mmHg, and HCO₃⁻ 20 mEq/L. What is the interpretation?
A: Partially compensated respiratory alkalosis. - Q: What treatment is recommended?
A: Supplemental oxygen and descent to a lower altitude.
Case 7: Shock
- Q: A patient in septic shock has pH 7.20, PaCO₂ 35 mmHg, and HCO₃⁻ 14 mEq/L. What is the interpretation?
A: Metabolic acidosis with no respiratory compensation. - Q: What is the primary cause of acidosis in this case?
A: Lactic acidosis from tissue hypoperfusion.
Rapid-Fire Scenarios
- Q: pH 7.50, PaCO₂ 40 mmHg, HCO₃⁻ 30 mEq/L.
A: Metabolic alkalosis. - Q: pH 7.28, PaCO₂ 60 mmHg, HCO₃⁻ 26 mEq/L.
A: Respiratory acidosis with no compensation. - Q: pH 7.35, PaCO₂ 55 mmHg, HCO₃⁻ 30 mEq/L.
A: Fully compensated respiratory acidosis. - Q: pH 7.41, PaCO₂ 30 mmHg, HCO₃⁻ 18 mEq/L.
A: Fully compensated respiratory alkalosis.
Critical Care Scenarios
- Q: A patient with a head injury has pH 7.22, PaCO₂ 55 mmHg, and HCO₃⁻ 24 mEq/L. What is the likely cause?
A: Respiratory acidosis due to hypoventilation from CNS depression. - Q: A patient with ARDS on mechanical ventilation has pH 7.30, PaCO₂ 50 mmHg, and HCO₃⁻ 24 mEq/L. What does this indicate?
A: Respiratory acidosis with no compensation. - Q: A burn patient develops pH 7.18, PaCO₂ 30 mmHg, and HCO₃⁻ 12 mEq/L. What is the interpretation?
A: Metabolic acidosis with partial respiratory compensation. - Q: What is the typical acid-base disturbance in septic shock?
A: Metabolic acidosis due to lactic acidosis. - Q: A patient with massive blood loss has pH 7.20, PaCO₂ 38 mmHg, and HCO₃⁻ 14 mEq/L. What is the diagnosis?
A: Metabolic acidosis due to hypoperfusion and lactic acidosis.
Special Populations
- Q: What acid-base disturbance is seen in newborns with respiratory distress syndrome (RDS)?
A: Respiratory acidosis. - Q: A patient with Cushing’s syndrome has pH 7.48, PaCO₂ 48 mmHg, and HCO₃⁻ 36 mEq/L. What is the interpretation?
A: Metabolic alkalosis with partial respiratory compensation. - Q: A patient with an acute asthma attack has pH 7.28, PaCO₂ 60 mmHg, and HCO₃⁻ 24 mEq/L. What is the diagnosis?
A: Respiratory acidosis. - Q: What acid-base disturbance is common in pregnancy?
A: Mild respiratory alkalosis due to increased minute ventilation.
Mnemonic Practice
High Anion Gap Metabolic Acidosis: “MUDPILES”
- Q: What does the “M” in MUDPILES stand for?
A: Methanol poisoning. - Q: What does the “U” in MUDPILES stand for?
A: Uremia (renal failure). - Q: What does the “D” in MUDPILES stand for?
A: Diabetic ketoacidosis. - Q: What does the “P” in MUDPILES stand for?
A: Propylene glycol or Paraldehyde. - Q: What does the “I” in MUDPILES stand for?
A: Isoniazid or Iron overdose. - Q: What does the “L” in MUDPILES stand for?
A: Lactic acidosis. - Q: What does the “E” in MUDPILES stand for?
A: Ethylene glycol poisoning. - Q: What does the “S” in MUDPILES stand for?
A: Salicylates (aspirin overdose).
Causes of Respiratory Acidosis: “CNS DEPRESS”
- Q: What does “C” in CNS DEPRESS stand for?
A: CNS depression (e.g., head injury, sedatives). - Q: What does “N” in CNS DEPRESS stand for?
A: Neuromuscular diseases (e.g., myasthenia gravis). - Q: What does “S” in CNS DEPRESS stand for?
A: Severe airway obstruction (e.g., asthma, COPD).
Interpreting Compensatory Responses
Acidosis and Compensation
- Q: What is the compensatory response in metabolic acidosis?
A: Hyperventilation to decrease PaCO₂. - Q: What is the compensatory response in respiratory acidosis?
A: Increased renal retention of HCO₃⁻. - Q: How long does it take for full renal compensation to occur in chronic respiratory acidosis?
A: 3-5 days. - Q: A patient with chronic respiratory acidosis and PaCO₂ 70 mmHg has HCO₃⁻ 38 mEq/L. Is this compensation appropriate?
A: Yes, expected HCO₃⁻ = 24 + 4 × 3 = 36 mEq/L.
Case 8: Aspirin Overdose
- Q: A patient with salicylate poisoning has pH 7.38, PaCO₂ 20 mmHg, and HCO₃⁻ 12 mEq/L. What is the diagnosis?
A: Mixed metabolic acidosis and respiratory alkalosis. - Q: Why does salicylate poisoning cause respiratory alkalosis?
A: Salicylates stimulate the respiratory center, causing hyperventilation.
Case 9: Hyperkalemia
- Q: How does hyperkalemia affect acid-base balance?
A: It can cause metabolic acidosis by shifting H⁺ ions out of cells. - Q: How is metabolic acidosis treated in hyperkalemia?
A: IV bicarbonate and insulin/glucose to shift potassium into cells.
Case 10: Drug Overdose
- Q: A patient with opioid overdose has pH 7.25, PaCO₂ 60 mmHg, and HCO₃⁻ 26 mEq/L. What is the interpretation?
A: Respiratory acidosis with no compensation. - Q: What is the immediate treatment?
A: Administer naloxone and support ventilation.
More Interpretation Practice
- Q: pH 7.50, PaCO₂ 35 mmHg, HCO₃⁻ 29 mEq/L.
A: Metabolic alkalosis with no respiratory compensation. - Q: pH 7.29, PaCO₂ 60 mmHg, HCO₃⁻ 28 mEq/L.
A: Respiratory acidosis with partial compensation. - Q: pH 7.48, PaCO₂ 52 mmHg, HCO₃⁻ 35 mEq/L.
A: Metabolic alkalosis with partial respiratory compensation. - Q: pH 7.20, PaCO₂ 40 mmHg, HCO₃⁻ 14 mEq/L.
A: Metabolic acidosis with no respiratory compensation. - Q: pH 7.44, PaCO₂ 28 mmHg, HCO₃⁻ 18 mEq/L.
A: Fully compensated respiratory alkalosis.
Rare Acid-Base Disorders
- Q: What is “renal tubular acidosis”?
A: A condition causing metabolic acidosis due to impaired renal bicarbonate reabsorption or H⁺ secretion. - Q: What acid-base imbalance is common in Addison’s disease?
A: Metabolic acidosis due to reduced aldosterone levels. - Q: What acid-base disorder occurs in Conn’s syndrome (hyperaldosteronism)?
A: Metabolic alkalosis.
- Q: Respiratory alkalosis is characterized by __________ PaCO₂ and __________ pH.
A: Decreased; increased. - Q: Metabolic acidosis is compensated by __________ to __________ PaCO₂.
A: Hyperventilation; decrease.
GIPHY App Key not set. Please check settings