Arterial Blood Gas Interpretation for NCLEX Practice Quiz

Arterial Blood Gas Interpretation for NCLEX Practice Quiz

 

Basics of ABG Interpretation

 

1. Q: What is the normal range for pH in an arterial blood gas?
   A: 7.35 – 7.45
2. Q: What is the normal range for PaCO₂?
   A: 35 – 45 mmHg
3. Q: What is the normal range for HCO₃⁻ (bicarbonate)?
   A: 22 – 26 mEq/L
4. Q: What is the normal range for PaO₂?
   A: 80 – 100 mmHg
5. Q: What is the normal range for oxygen saturation (SaO₂)?
   A: 95 – 100%
6. Q: What is the term for a pH below 7.35?
   A: Acidosis
7. Q: What is the term for a pH above 7.45?
   A: Alkalosis
8. Q: What does PaCO₂ primarily reflect?
   A: Respiratory function
9. Q: What does HCO₃⁻ primarily reflect?
   A: Metabolic function
10. Q: Which organ regulates bicarbonate levels?
    A: Kidneys

 

Acidosis and Alkalosis Types

 

11. Q: What condition is indicated by pH < 7.35 and PaCO₂ > 45 mmHg?
    A: Respiratory acidosis
12. Q: What condition is indicated by pH > 7.45 and PaCO₂ < 35 mmHg?
    A: Respiratory alkalosis
13. Q: What condition is indicated by pH < 7.35 and HCO₃⁻ < 22 mEq/L?
    A: Metabolic acidosis
14. Q: What condition is indicated by pH > 7.45 and HCO₃⁻ > 26 mEq/L?
    A: Metabolic alkalosis
15. Q: Which acid-base disturbance is most likely in a patient with severe diarrhea?
    A: Metabolic acidosis
16. Q: Which acid-base disturbance is most likely in a patient with prolonged vomiting?
    A: Metabolic alkalosis
17. Q: What is the primary compensatory mechanism for metabolic acidosis?
    A: Increased respiratory rate to decrease PaCO₂
18. Q: What is the primary compensatory mechanism for respiratory acidosis?
    A: Increased renal retention of bicarbonate
19. Q: What does a normal pH with abnormal PaCO₂ and HCO₃⁻ indicate?
    A: Full compensation
20. Q: Which acid-base disturbance is common in hyperventilation due to anxiety?
    A: Respiratory alkalosis

Advanced ABG Scenarios

 

21. Q: A patient has pH 7.32, PaCO₂ 50 mmHg, and HCO₃⁻ 24 mEq/L. What is the interpretation?
    A: Respiratory acidosis
22. Q: A patient has pH 7.48, PaCO₂ 30 mmHg, and HCO₃⁻ 23 mEq/L. What is the interpretation?
    A: Respiratory alkalosis
23. Q: A patient has pH 7.28, PaCO₂ 38 mmHg, and HCO₃⁻ 18 mEq/L. What is the interpretation?
    A: Metabolic acidosis
24. Q: A patient has pH 7.50, PaCO₂ 40 mmHg, and HCO₃⁻ 30 mEq/L. What is the interpretation?
    A: Metabolic alkalosis
25. 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

 

26. 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.
27. Q: What is indicated by pH 7.45, PaCO₂ 25 mmHg, and HCO₃⁻ 18 mEq/L?
    A: Mixed respiratory alkalosis and metabolic acidosis.
28. Q: Can full compensation occur in a mixed acid-base disorder?
    A: No, full compensation is not possible in mixed disorders.

Common Clinical Scenarios

 

29. 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.
30. Q: What acid-base disturbance is associated with diabetic ketoacidosis?
    A: Metabolic acidosis.
31. Q: What acid-base disturbance is common in patients with renal failure?
    A: Metabolic acidosis.
32. 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.
33. 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.
34. Q: What acid-base disturbance is common in aspirin overdose?
    A: Mixed respiratory alkalosis and metabolic acidosis.
35. Q: What acid-base disturbance is common in sepsis?
    A: Metabolic acidosis due to lactic acidosis.
36. Q: What acid-base disturbance is expected in a patient with hypoventilation?
    A: Respiratory acidosis.

Oxygenation Questions

 

37. Q: What does a PaO₂ of less than 60 mmHg indicate?
    A: Hypoxemia.
38. Q: What does a PaO₂ of more than 100 mmHg indicate?
    A: Hyperoxemia.
39. Q: What is the normal alveolar-arterial (A-a) gradient for a healthy young adult?
    A: Less than 15 mmHg.
40. Q: What oxygenation parameter is most affected in carbon monoxide poisoning?
    A: SaO₂ (oxygen saturation).
41. Q: What oxygen delivery device is used for a PaO₂ below 60 mmHg on room air?
    A: Non-rebreather mask or mechanical ventilation.
42. Q: What does a high A-a gradient suggest?
    A: Impaired oxygen diffusion, ventilation-perfusion mismatch, or shunt.

Compensation Mechanisms

 

43. Q: How long does renal compensation for respiratory acidosis take?
    A: 24-48 hours.
44. Q: How does the body compensate for metabolic alkalosis?
    A: Hypoventilation to retain CO₂.
45. Q: What indicates partial compensation in ABG results?
    A: Abnormal pH, with one parameter compensating.
46. Q: What indicates no compensation in ABG results?
    A: Abnormal pH with no change in the compensating parameter.

Advanced ABG Calculations

 

47. Q: How do you calculate anion gap?
    A: Na⁺ – (Cl⁻ + HCO₃⁻).
48. Q: What is the normal anion gap range?
    A: 8-12 mEq/L.
49. Q: What conditions cause a high anion gap metabolic acidosis?
    A: Ketoacidosis, lactic acidosis, renal failure, or toxin ingestion (MUDPILES mnemonic).
50. Q: What conditions cause a normal anion gap metabolic acidosis?
    A: Diarrhea, renal tubular acidosis, or saline infusion.
51. Q: How do you calculate expected PaCO₂ in metabolic acidosis (using Winter’s formula)?
    A: Expected PaCO₂ = (1.5 × HCO₃⁻) + 8 ± 2.
52. 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.
53. Q: What does a higher-than-expected PaCO₂ in metabolic acidosis indicate?
    A: Co-existing respiratory acidosis.
54. Q: What does a lower-than-expected PaCO₂ in metabolic acidosis indicate?
    A: Co-existing respiratory alkalosis.

Clinical Practice Scenarios

 

55. Q: A patient has pH 7.40, PaCO₂ 28 mmHg, and HCO₃⁻ 18 mEq/L. What is the interpretation?
    A: Fully compensated respiratory alkalosis.
56. 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.
57. 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.
58. Q: What acid-base disorder is suggested by low pH, high PaCO₂, and high HCO₃⁻?
    A: Partially compensated respiratory acidosis.
59. Q: What acid-base disorder is suggested by high pH, low PaCO₂, and low HCO₃⁻?
    A: Partially compensated respiratory alkalosis.
60. 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

 

61. 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.
62. 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.
63. 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.
64. 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.
65. 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

 

66. 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.
67. 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)

 

68. 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.
69. Q: What lab test can confirm the underlying cause?
    A: Serum ketone levels.
70. Q: What is the primary treatment for the above case?
    A: IV insulin and fluid replacement to correct acidosis.

Case 3: Panic Attack

 

71. 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.
72. Q: What is the recommended management?
    A: Reassurance and coaching in breathing techniques (e.g., breathing into a paper bag).

Case 4: Renal Failure

 

73. 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.
74. Q: What is the priority treatment?
    A: Correct metabolic acidosis with sodium bicarbonate and manage underlying kidney disease.

Case 5: Mixed Disorder

 

75. 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.
76. 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

 

77. Q: What acid-base disturbance is common during a blood transfusion reaction?
    A: Metabolic acidosis.
78. Q: What acid-base disturbance is seen in pregnancy?
    A: Mild respiratory alkalosis due to increased minute ventilation.
79. Q: What acid-base imbalance is likely with overdose of opioids?
    A: Respiratory acidosis.
80. Q: What is the typical ABG in a patient with ARDS on high ventilator settings?
    A: Mixed respiratory acidosis and hypoxemia.

Compensation Review Questions

 

81. Q: What compensates first: lungs or kidneys?
    A: Lungs, as respiratory compensation is faster.
82. Q: Why does metabolic compensation take longer?
    A: Renal processes, like bicarbonate retention, require 24-48 hours.
83. Q: How can you confirm that compensation is appropriate?
    A: By checking if PaCO₂ or HCO₃⁻ matches the expected compensation formula.

True/False Practice

 

84. Q: In respiratory acidosis, renal compensation begins immediately.
    A: False (it takes 24-48 hours).
85. Q: In metabolic alkalosis, hypoventilation fully normalizes the pH.
    A: False (hypoventilation is limited due to hypoxia risk).
86. Q: A normal PaCO₂ excludes a respiratory component in mixed disorders.
    A: False.
87. Q: Hypoxia can occur with a normal PaO₂ if hemoglobin is low.
    A: True.

Case 6: High-Altitude Sickness

 

88. Q: A mountaineer has pH 7.48, PaCO₂ 28 mmHg, and HCO₃⁻ 20 mEq/L. What is the interpretation?
    A: Partially compensated respiratory alkalosis.
89. Q: What treatment is recommended?
    A: Supplemental oxygen and descent to a lower altitude.

Case 7: Shock

 

90. 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.
91. Q: What is the primary cause of acidosis in this case?
    A: Lactic acidosis from tissue hypoperfusion.

Rapid-Fire Scenarios

 

92. Q: pH 7.50, PaCO₂ 40 mmHg, HCO₃⁻ 30 mEq/L.
    A: Metabolic alkalosis.
93. Q: pH 7.28, PaCO₂ 60 mmHg, HCO₃⁻ 26 mEq/L.
    A: Respiratory acidosis with no compensation.
94. Q: pH 7.35, PaCO₂ 55 mmHg, HCO₃⁻ 30 mEq/L.
    A: Fully compensated respiratory acidosis.
95. Q: pH 7.41, PaCO₂ 30 mmHg, HCO₃⁻ 18 mEq/L.
    A: Fully compensated respiratory alkalosis.

 

Critical Care Scenarios

 

96. 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.
97. 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.
98. 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.
99. Q: What is the typical acid-base disturbance in septic shock?
    A: Metabolic acidosis due to lactic acidosis.
100. 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

 

101. Q: What acid-base disturbance is seen in newborns with respiratory distress syndrome (RDS)?
     A: Respiratory acidosis.
102. 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.
103. 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.
104. 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”

 

105. Q: What does the “M” in MUDPILES stand for?
     A: Methanol poisoning.
106. Q: What does the “U” in MUDPILES stand for?
     A: Uremia (renal failure).
107. Q: What does the “D” in MUDPILES stand for?
     A: Diabetic ketoacidosis.
108. Q: What does the “P” in MUDPILES stand for?
     A: Propylene glycol or Paraldehyde.
109. Q: What does the “I” in MUDPILES stand for?
     A: Isoniazid or Iron overdose.
110. Q: What does the “L” in MUDPILES stand for?
     A: Lactic acidosis.
111. Q: What does the “E” in MUDPILES stand for?
     A: Ethylene glycol poisoning.
112. Q: What does the “S” in MUDPILES stand for?
     A: Salicylates (aspirin overdose).

Causes of Respiratory Acidosis: “CNS DEPRESS”

 

113. Q: What does “C” in CNS DEPRESS stand for?
     A: CNS depression (e.g., head injury, sedatives).
114. Q: What does “N” in CNS DEPRESS stand for?
     A: Neuromuscular diseases (e.g., myasthenia gravis).
115. Q: What does “S” in CNS DEPRESS stand for?
     A: Severe airway obstruction (e.g., asthma, COPD).

Interpreting Compensatory Responses

Acidosis and Compensation

 

116. Q: What is the compensatory response in metabolic acidosis?
     A: Hyperventilation to decrease PaCO₂.
117. Q: What is the compensatory response in respiratory acidosis?
     A: Increased renal retention of HCO₃⁻.
118. Q: How long does it take for full renal compensation to occur in chronic respiratory acidosis?
     A: 3-5 days.
119. 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

 

120. 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.
121. Q: Why does salicylate poisoning cause respiratory alkalosis?
     A: Salicylates stimulate the respiratory center, causing hyperventilation.

Case 9: Hyperkalemia

 

122. Q: How does hyperkalemia affect acid-base balance?
     A: It can cause metabolic acidosis by shifting H⁺ ions out of cells.
123. Q: How is metabolic acidosis treated in hyperkalemia?
     A: IV bicarbonate and insulin/glucose to shift potassium into cells.

Case 10: Drug Overdose

 

124. 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.
125. Q: What is the immediate treatment?
     A: Administer naloxone and support ventilation.

More Interpretation Practice

 

126. Q: pH 7.50, PaCO₂ 35 mmHg, HCO₃⁻ 29 mEq/L.
     A: Metabolic alkalosis with no respiratory compensation.
127. Q: pH 7.29, PaCO₂ 60 mmHg, HCO₃⁻ 28 mEq/L.
     A: Respiratory acidosis with partial compensation.
128. Q: pH 7.48, PaCO₂ 52 mmHg, HCO₃⁻ 35 mEq/L.
     A: Metabolic alkalosis with partial respiratory compensation.
129. Q: pH 7.20, PaCO₂ 40 mmHg, HCO₃⁻ 14 mEq/L.
     A: Metabolic acidosis with no respiratory compensation.
130. Q: pH 7.44, PaCO₂ 28 mmHg, HCO₃⁻ 18 mEq/L.
     A: Fully compensated respiratory alkalosis.

Rare Acid-Base Disorders

 

131. Q: What is “renal tubular acidosis”?
     A: A condition causing metabolic acidosis due to impaired renal bicarbonate reabsorption or H⁺ secretion.
132. Q: What acid-base imbalance is common in Addison’s disease?
     A: Metabolic acidosis due to reduced aldosterone levels.
133. Q: What acid-base disorder occurs in Conn’s syndrome (hyperaldosteronism)?
     A: Metabolic alkalosis.

 

134. Q: Respiratory alkalosis is characterized by __________ PaCO₂ and __________ pH.
     A: Decreased; increased.
135. Q: Metabolic acidosis is compensated by __________ to __________ PaCO₂.
     A: Hyperventilation; decrease.