Arterial Blood Gas (ABG) Practice Questions and Answers

Arterial blood gas (ABG) analysis is a critical diagnostic tool used to assess a patient’s oxygenation, ventilation, and acid-base balance. Understanding how to interpret ABG results is essential for healthcare professionals, especially respiratory therapists.

This article provides a comprehensive list of ABG practice questions and answers to help reinforce key concepts, including the causes and corrections of acid-base imbalances, oxygenation principles, and proper ABG sampling techniques.

What is an Arterial Blood Gas?

An arterial blood gas (ABG) is a test that measures the levels of oxygen (O₂), carbon dioxide (CO₂), and pH in arterial blood. It helps assess lung function, acid-base balance, and overall oxygenation in the body.

ABG results are crucial in diagnosing and managing respiratory conditions like COPD, asthma, and respiratory failure. The test involves drawing blood from an artery, usually the radial artery, and analyzing key parameters such as PaO₂, PaCO₂, pH, HCO₃⁻, and SaO₂.

ABGs are commonly used in critical care, emergency medicine, and mechanical ventilation management to guide treatment decisions.

ABG Practice Questions and Answers

1. What are the causes of respiratory acidosis?  
Respiratory acidosis occurs due to CO₂ retention in the blood, commonly caused by hypoventilation, increased dead space, airway obstruction, neuromuscular disorders, and lung diseases such as COPD.

2. How can respiratory acidosis be corrected?  
Increase the respiratory rate (breaths per minute), increase tidal volume, reduce dead space, and treat the underlying cause such as airway obstruction or neuromuscular impairment.

3. What are the causes of respiratory alkalosis?  
Respiratory alkalosis is caused by excessive CO₂ elimination due to hyperventilation, pain, anxiety, fever, hypoxemia, or stimulation of the respiratory center in the brain.

4. How can respiratory alkalosis be corrected?  
Reduce the respiratory rate, treat pain or fever, provide sedation for anxiety if necessary, and correct any underlying metabolic causes.

5. What are the causes of metabolic acidosis?  
Metabolic acidosis results from a decrease in HCO₃ levels, commonly caused by diarrhea, aspirin toxicity, diabetic ketoacidosis (DKA), renal failure, or lactic acidosis.

6. How can metabolic acidosis be corrected?  
Identify and treat the underlying cause, administer bicarbonate if necessary, provide insulin for diabetic ketoacidosis, and manage renal failure appropriately.

7. What are the causes of metabolic alkalosis?  
Metabolic alkalosis is caused by an excessive increase in HCO₃, which can result from vomiting, nasogastric (NG) suctioning, excessive ingestion of sodium bicarbonate (NaHCO₃), or diuretic use.

8. How can metabolic alkalosis be corrected?  
Treat the underlying cause by stopping vomiting, discontinuing NG suctioning, correcting electrolyte imbalances, and avoiding excessive bicarbonate administration.

9. What is oxygenation?  
Oxygenation refers to the level of oxygen dissolved in plasma, represented by the PaO₂, which is measured through arterial blood gas (ABG) analysis.

10. What should be done before performing an ABG?  
Check the patient’s medical chart to verify the physician’s order, review the indication for the procedure, and assess coagulation status.

11. What is the preferred site for an ABG in adults?  
The radial artery is the preferred site due to its accessibility and collateral circulation from the ulnar artery.

12. What is the maximum time an ABG sample can go without ice before analysis?  
An ABG sample should be analyzed within 15 minutes if not placed on ice.

13. What test is performed to confirm collateral circulation before an ABG puncture?  
The Modified Allen Test is performed to ensure adequate collateral circulation from the ulnar artery.

14. What is the adequate blood volume for an ABG sample?  
An ABG sample should contain 2-4 mL of arterial blood.

15. What are some additional causes of metabolic acidosis?  
Other causes include severe dehydration, sepsis, shock, kidney disease, and alcohol poisoning.

16. What are the three major risks of an arterial puncture?  
The primary risks include excessive bleeding, arterial obstruction, and infection.

17. What are the three main criteria for selecting an arterial puncture site?  
Collateral circulation, vessel accessibility, and the absence of sensitive nearby structures such as nerves.

18. What is collateral blood flow?  
Collateral circulation ensures that blood flow continues through an alternative artery in case the punctured artery becomes obstructed.

19. What is vessel accessibility?  
The ideal artery for puncture should be easily palpable, located superficially, and stable.

20. What are peripheral structures, and why are they important in ABG selection?  
Peripheral structures include nerves and veins near the artery. An ideal puncture site should avoid highly sensitive adjacent structures to minimize the risk of complications.

21. How is the Modified Allen Test performed?  
The patient raises their hand and makes a fist for 20 seconds. The examiner compresses both the radial and ulnar arteries. The patient then opens their hand, which should appear pale. The examiner releases pressure on the ulnar artery while maintaining pressure on the radial artery. If the hand flushes pink within 5-10 seconds, collateral circulation is adequate.

22. What are alternative methods for assessing collateral circulation?  
Doppler ultrasound and pulse oximetry can be used if the Modified Allen Test is inconclusive.

23. What blood gas parameter is most useful for assessing oxygenation status?  
PaO₂ is the best indicator of arterial oxygenation.

24. An increase in CO₂ causes pH levels to shift in which direction?  
An increase in CO₂ causes pH levels to decrease, leading to acidosis.

25. A patient presents with the following ABG results: pH 7.52, PaCO₂ 25 mmHg, HCO₃ 25 mEq/L, BE +1. What is the interpretation?  
The patient has respiratory alkalosis due to low PaCO₂ and an uncompensated pH imbalance.

26. A patient has a pH of 7.10, PaCO₂ of 20 mmHg, HCO₃ of 10 mEq/L, and BE of -20. What is your interpretation of this blood gas?  
Metabolic Acidosis

27. What value do you assess in an ABG to determine ventilation status?  
PaCO₂

28. Can a blood gas be considered normal if the base excess (BE) is not within normal limits?  
No; for an ABG to be considered normal, all parameters must fall within the normal range.

29. If an ABG shows a normal pH while PaCO₂ and HCO₃ are moving in the same direction, how would you classify the blood gas?  
Fully compensated

30. An ABG reads: pH 7.56, PaCO₂ 42 mmHg, HCO₃ 34 mEq/L, and BE +5. How would you interpret this blood gas?  
Acute/Uncompensated Metabolic Alkalosis

31. At what pH level is intubation generally indicated?  
A pH of 7.2 or below

32. Severe hypoxemia is classified as a PaO₂ below what level?  
Less than 40 mmHg

33. What is the normal PaO₂ range for a patient breathing room air?  
80-100 mmHg

34. What is the PaO₂ range for moderate hypoxemia?  
40-59 mmHg

35. An ABG reads: pH 7.42, PaCO₂ 43 mmHg, HCO₃ 25 mEq/L, and BE +2. How would you interpret this blood gas?  
Normal ABG

36. If the pH falls below 7.35, the blood is considered to be what?  
Acidic

37. If the pH rises above 7.45, the blood is considered to be what?  
Alkalotic

38. If a patient is hypoventilating, what happens to their PaCO₂?  
PaCO₂ will increase.

39. If a patient is hyperventilating, what happens to their PaCO₂?  
PaCO₂ will decrease.

40. Which drugs can cause a low pH (acidosis)?  
Narcotics, barbiturates, acetazolamide (Diamox), ammonium chloride, and paraldehyde.

41. Which drugs can cause an elevated pH (alkalosis)?  
Sodium bicarbonate, sodium oxalate, and potassium oxalate.

42. The primary goal of acid-base homeostasis is to maintain what?  
A normal pH.

43. What are common causes of respiratory alkalosis?  
Anxiety, hypoxemia, and pain.

44. Which organ system is responsible for maintaining normal HCO₃ levels at approximately 24 mEq/L?  
The renal system.

45. What is the limiting factor for H+ excretion in the renal tubules?  
Insufficient buffers.

46. What acts as the first-line defense against excessive accumulation of H+ ions in the blood?  
The blood buffer systems.

47. How do you determine if a blood gas imbalance is primarily a respiratory problem?  
If PaCO₂ is less than 35 mmHg (respiratory alkalosis) or greater than 45 mmHg (respiratory acidosis).

48. How do you determine if a blood gas imbalance is primarily a metabolic problem?  
If HCO₃ is less than 22 mEq/L (metabolic acidosis) or greater than 26 mEq/L (metabolic alkalosis).

49. If a patient has a pH of 7.49, how would this be classified?  
Alkalosis

50. What are the common sites for placing a transcutaneous blood gas electrode?  
Chest, abdomen, and lower back.

51. What are the common sites for arterial blood sampling via percutaneous needle puncture?  
Radial, femoral, and brachial arteries.

52. Before obtaining a capillary blood sample, what should be done to the puncture site?  
Warm the site to 42°C and clean it with an antiseptic solution.

53. A mechanically ventilated patient experiences a sudden drop in end-tidal CO₂ levels. What are possible causes?  
Massive pulmonary embolism, ventilator disconnection, and a sudden decrease in cardiac output.

54. What factors determine the volume needed for an arterial blood sample?  
The ABG analyzer’s requirements, the specific anticoagulant used, and any additional tests to be performed.

55. What steps should be taken after obtaining an arterial blood sample?  
Apply pressure to the site until bleeding stops, place the sample in a transport container with ice slush, and mix the sample by rolling and inverting the syringe.

56. When is transcutaneous blood gas monitoring indicated?  
To continuously monitor gas exchange in infants and children, assess real-time responses to bedside interventions, and detect hyperoxia in newborns.

57. What size needle is recommended for obtaining an ABG sample from an infant?  
25-gauge needle.

58. What are the indications for arterial blood sampling via percutaneous needle puncture?  
Monitoring disease severity, evaluating ventilation and acid-base status, and assessing a patient’s response to therapy.

59. After obtaining an arterial blood sample from an arterial line, what steps should you take?  
Flush the line and stopcock with heparinized intravenous solution, confirm the stopcock is open to the IV bag solution and catheter, and verify an undamped pulse pressure waveform on the monitor.

60. What patient parameters should be assessed before arterial blood sampling?  
Temperature, position and activity level, and overall clinical appearance.

61. What are the clinical signs of acute respiratory alkalosis?  
Convulsions, dizziness, and paresthesia.

62. A low PaCO₂ is characteristic of what condition?  
Respiratory alkalosis.

63. In partially compensated respiratory alkalosis, which blood gas abnormalities would you expect?  
Decreased HCO₃, decreased PaCO₂, and increased pH.

64. What are common causes of respiratory acidosis in patients with normal lungs?  
Neuromuscular disorders, spinal cord trauma, anesthesia, and central nervous system depression.

65. Before connecting the sample syringe to an adult arterial line stopcock, what precaution should be taken?  
Aspirate at least 5 mL of fluid or blood using a waste syringe.

66. What equipment is required for capillary blood sampling?  
Lancet, capillary tubes, and a warming pad.

67. When is capillary blood gas sampling indicated?  
When an ABG analysis is needed but arterial access is unavailable.

68. How does the body compensate for metabolic acidosis?  
By decreasing blood CO₂ levels through increased respiratory rate.

69. What are common causes of metabolic alkalosis?  
Diuretics, hypochloremia, and vomiting.

70. What blood gas findings would you expect in a fully compensated respiratory acidosis patient?  
An elevated HCO₃ and a pH between 7.35 and 7.39.

71. What is the normal pH range?  
7.35-7.45

72. What is the normal range for PaCO₂?  
35-45 mmHg

73. What is the normal range for HCO₃?  
22-26 mEq/L

74. What is the normal range for base excess?  
-2 to +2 mEq/L

75. What type of abnormalities are evaluated using HCO₃ and base excess values?  
Metabolic disorders.

76. What type of issues are assessed by evaluating PaCO₂ values?  
Ventilation status.

77. What does PaO₂ measure?  
Oxygenation status.

78. What is the normal range for PaO₂ on room air?  
80-100 mmHg.

79. Which ABG value is relevant for patients who currently smoke or have a history of heavy smoking?  
% MetHb (Methemoglobin).

80. Which ABG value is important for patients with carbon monoxide poisoning or those exposed to fire?  
% COHb (Carboxyhemoglobin).

81. In an ABG, if the pH and CO₂ values move in opposite directions, what does this indicate?  
A respiratory-related condition.

82. In an ABG, if the pH and HCO₃ values move in the same direction, what does this indicate?  
A metabolic-related condition.

83. When interpreting an ABG, what must be abnormal for the condition to be considered “partially compensated”?  
All three values (pH, CO₂, and HCO₃) must be abnormal.

84. When interpreting an ABG, what must be normal for the condition to be considered “uncompensated”?  
Either the CO₂ or HCO₃ must be within normal limits.

85. When interpreting an ABG, what must be normal for the condition to be considered “fully compensated”?  
The pH must be within normal limits.

86. How can pre-analytical errors in ABG samples be prevented?  
Ensure the sample is obtained anaerobically, properly anticoagulated, free of air bubbles, and analyzed within 10-30 minutes.

87. How is CO₂ transported in the blood?  
CO₂ is transported as ionized bicarbonate (HCO₃), dissolved in plasma, and bound to plasma proteins.

88. How much blood is required for an adequate ABG sample?  
0.5 mL, which is typically sufficient for two tests.

89. What are the key components of quality control for accurate ABG analysis?  
Recordkeeping, performance validation, preventive maintenance, function checks, automated calibration, internal statistical quality control, and external quality control.

90. What are common indications for drawing an ABG?  
Sudden dyspnea, tachypnea, abnormal breath sounds, cyanosis, increased accessory muscle use, changes in ventilator settings, CPR, abnormal chest X-ray findings, sudden cardiac arrhythmias, and acute hypotension.

91. What factors affect the accuracy of ABG analysis?  
Accurate barometric pressure measurement, proper calibration against known values, electrode maintenance, and adherence to quality control procedures.

92. How does inadequate warming and excessive squeezing of the puncture site affect an ABG sample?  
It can lead to venous and lymphatic contamination of the sample.

93. What are the secondary values calculated from ABG analysis?  
Bicarbonate (HCO₃), base excess (BE) or deficit, and hemoglobin saturation (HbO₂).

94. What are the benefits of using indwelling arterial catheters?  
They provide continuous access for blood sampling and allow for real-time monitoring of vascular pressures.

95. What are two common sites for indwelling arterial catheters?  
Peripheral arteries (radial, brachial, pedal) and central arteries (femoral, pulmonary artery).

96. What can a capillary blood gas sample estimate?  
It provides an approximation of arterial oxygenation and PCO₂ levels.

97. What can be used for frequent blood sampling in critically ill patients?  
Arterial cannulation.

98. What is hemoximetry?  
A laboratory procedure used to measure hemoglobin levels and oxygen saturation through invasive arterial blood sampling.

99. What ABG value determines a patient’s ventilation status?  
PaCO₂.

100. What is the general rule regarding the relationship between PaO₂ and FiO₂?  
PaO₂ should be approximately five times the FiO₂.

101. Does oxygenation decrease with age?  
Yes, oxygenation tends to decrease as a person ages due to physiological changes in lung function.

102. What happens when an ABG is partially compensated?  
The pH remains out of the normal range, while both CO₂ and HCO₃ levels move in the same direction as the body attempts to compensate.

103. What is the normal value for COHb (Carboxyhemoglobin)?  
Less than 3.0%.

104. What does an elevated COHb indicate?  
It suggests exposure to carbon monoxide, such as from smoke inhalation or house fires.

105. What is the normal value for MetHb (Methemoglobin)?  
Less than 2.0%.

106. What does an elevated MetHb indicate?  
It may indicate exposure to oxidizing agents, congenital methemoglobinemia, or chronic smoking.

107. Why is ABG analysis important?  
ABG analysis provides critical information for managing patients with respiratory and metabolic disorders by assessing oxygenation, ventilation, and acid-base status.

108. What does pH represent in an ABG?  
It reflects the overall acid-base balance of the blood, indicating hydrogen ion concentration.

109. What does PaCO₂ represent?  
It represents the level of arterial carbon dioxide and is used to evaluate a patient’s ventilatory status.

110. What does PaO₂ represent?  
It indicates the oxygen tension in arterial blood and helps assess oxygenation status.

111. What does HCO₃ represent?  
It represents the bicarbonate concentration in the blood, which plays a key role in maintaining acid-base balance.

112. What does BE (Base Excess) represent?  
It indicates the amount of excess or deficit of bicarbonate in the blood, helping to assess the metabolic component of acid-base balance.

113. What does SaO₂ represent?  
It measures the percentage of hemoglobin saturated with oxygen in arterial blood, reflecting overall oxygenation.

114. What is compensation in acid-base balance?  
It refers to the body’s adjustments via the respiratory or renal system to correct an acid-base imbalance.

115. What is hypoxemia?  
A condition characterized by abnormally low levels of oxygen in the blood.

116. How does minute ventilation affect ABG interpretation?  
An increase in minute ventilation lowers PaCO₂ and raises pH (leading to alkalosis), while a decrease in minute ventilation raises PaCO₂ and lowers pH (leading to acidosis).

117. What are the indications for obtaining an ABG?  
To monitor ABG values, assess response to therapeutic or diagnostic interventions, and evaluate disease progression or severity.

118. Why is the femoral artery considered risky for an ABG stick?  
It is near large veins and arteries, increasing the risk of accidental venous puncture, excessive bleeding, and infection. It is also contraindicated in patients receiving fibrinolytic therapy.

119. Why is the radial artery the preferred site for an ABG stick?  
It has good collateral circulation, is superficial and easy to palpate, is not near large veins, and has a lower risk of complications compared to other sites.

120. Why is the brachial artery a less desirable site for an ABG stick?  
It lacks collateral circulation, is located near nerves and large veins, and carries a higher risk of obtaining a venous sample.

121. What are the contraindications for performing an ABG stick?  
Bleeding disorders, local infection at the puncture site, anticoagulation therapy, thrombolytic agents, vascular disease, arteriovenous fistulas, or vascular grafts.

122. What are the indications for placing an arterial line?  
Continuous arterial blood pressure monitoring and frequent arterial blood gas sampling.

123. What is the capillary blood gas (CBG) an alternative for?  
It can sometimes serve as an alternative to an arterial blood gas (ABG) sample when arterial access is unavailable.

124. What does a capillary blood gas provide in comparison to an ABG?  
It offers a rough estimate of pH and PaCO₂ but does not provide an accurate assessment of oxygenation (PaO₂) due to the nature of venous blood flow.

126. How is the ABG procedure performed?  
Blood is collected in a heparinized syringe or glass capillary tube, and the site should be warmed beforehand to improve blood flow.

127. What are some potential hazards of an ABG?  
The risks include infection, bleeding, hematoma formation, arterial spasm, and obstruction of the vessel.

128. What are the common sites for a capillary blood gas sample?  
The preferred sites include the lateral heel (for infants), the fingertip, and the earlobe.

129. What information does an ABG sample provide?  
ABG analysis provides precise measurements of acid-base balance, oxygenation, and the lungs’ ability to remove CO₂.

130. What is required for an accurate interpretation of an ABG?  
A thorough understanding of the patient’s overall clinical condition, including their medical history, current treatments, and ventilatory support.

131. Where are mixed venous blood samples drawn from?  
They are typically drawn from the pulmonary artery via a Swan-Ganz catheter or from the right atrium.

132. What is the purpose of a mixed venous blood sample?  
It helps evaluate overall tissue oxygenation and assess the balance between oxygen delivery and consumption.

133. Before performing an ABG draw, what should the respiratory therapist review in the patient’s chart?  
Check for bleeding disorders, anticoagulation therapy, low platelet count, or increased clotting time.

134. What must be evaluated before performing a radial artery puncture?  
Collateral circulation must be assessed using the modified Allen’s test.

135. How is the modified Allen’s test performed?  
The patient clenches their fist while both the radial and ulnar arteries are compressed. The patient then opens their hand while the ulnar artery is released. If the hand turns pink within 10-15 seconds, collateral circulation is adequate.

136. What does a positive Modified Allen’s test indicate?  
A positive result means that the hand turns pink within 10-15 seconds after releasing the ulnar artery, confirming sufficient collateral circulation.

137. What should the respiratory therapist do if the Modified Allen’s test is negative?  
Try the other arm. If the result is still negative, consider using the brachial artery or another alternative site.

138. What should be recommended for a patient requiring frequent ABGs?  
Insertion of an indwelling arterial catheter to minimize repeated needle sticks.

139. How do air bubbles in an ABG sample affect results?  
They can lead to inaccurate oxygen readings by artificially increasing the PaO₂ and decreasing the PaCO₂.

140. How should the respiratory therapist handle an ABG sample after collection?  
Remove air bubbles, store the sample in ice water to slow metabolism, and analyze it as soon as possible.

141. How soon should a room temperature ABG sample be analyzed?  
Ideally within 10-15 minutes to ensure accuracy.

142. How long should pressure be applied to an arterial puncture site?  
At least 3-5 minutes, or longer if the patient has a bleeding disorder or is on anticoagulants.

143. What is the role of the kidneys in acid-base balance?  
The kidneys help maintain acid-base homeostasis by excreting hydrogen ions and reabsorbing bicarbonate (HCO₃).

144. How is base excess (BE) interpreted?  
A positive base excess indicates excess bicarbonate or a loss of acid, while a negative value suggests metabolic acidosis.

145. Why is base excess important?  
It provides insight into the metabolic component of acid-base balance, helping differentiate between respiratory and metabolic disorders.

146. Do changes in PaCO₂ affect base excess?  
No, base excess is influenced only by metabolic factors, not by changes in ventilation.

147. What are common causes of respiratory acidosis?  
Acute upper airway obstruction, severe airway obstruction (acute or chronic), and massive pulmonary edema.

148. What are some non-respiratory conditions that can lead to respiratory acidosis?  
Drug overdose, neuromuscular diseases, spinal cord injury, head trauma, and thoracic cage trauma.

149. How is fully compensated respiratory acidosis defined?  
It occurs when HCO₃ has increased enough to bring the pH back within the normal range, despite elevated PaCO₂.

150. If expected HCO₃ compensation is not occurring in respiratory acidosis, what should be suspected?  
A complicating metabolic disorder may also be present, requiring further investigation.

151. In acute respiratory acidosis, how high does the PaCO₂ need to be for the patient to become comatose?  
Around 70 mmHg or higher.

152. Because CO₂ causes systemic vasodilation, what cardiac manifestations should be expected?  
Warm, flushed skin, bounding pulse, and arrhythmias.

153. How can respiratory alkalosis be identified on an ABG?  
PaCO₂ will be below the normal range, indicating excessive ventilation (hyperventilation).

154. What are common causes of respiratory alkalosis?  
Hyperventilation due to pain, hypoxemia (PaO₂ between 55-60 mmHg), metabolic acidosis, and anxiety.

155. How do the kidneys compensate for respiratory alkalosis?  
By excreting excess bicarbonate (HCO₃).

156. What are the clinical signs and symptoms associated with respiratory alkalosis?  
Tachypnea, dizziness, sweating, tingling in fingers and toes, muscle weakness, and muscle spasms.

157. When should a respiratory therapist be cautious about inducing respiratory alkalosis?  
During intermittent positive pressure breathing (IPPB) therapy and mechanical ventilation.

158. How does the body compensate for metabolic acidosis?  
By hyperventilating to blow off CO₂ and raise the pH.

159. What is the most common and obvious sign of metabolic acidosis?  
Kussmaul’s breathing (deep, labored breathing).

160. What are the most common causes of metabolic alkalosis?  
Hypokalemia, hypochloremia, nasogastric (NG) suctioning, vomiting, post-hypercapnic disorder, diuretics, steroids, or excessive bicarbonate administration.

161. How does the body compensate for metabolic alkalosis?  
By hypoventilating to retain CO₂.

162. What do ABG results determine?  
They assess oxygenation and acid-base balance and play a critical role in managing mechanical ventilation.

163. What does the pH measure?  
It measures the acidity or alkalinity of the blood.

164. What does the PaCO₂ measure?  
It measures the partial pressure of carbon dioxide in the blood, which reflects ventilation status.

165. What does the PaO₂ measure?  
It measures the partial pressure of oxygen in the blood, which indicates oxygenation status.

166. What does HCO₃ measure?  
It measures the concentration of bicarbonate in the blood, which reflects metabolic function.

167. What are the three classifications of an ABG result?  
Normal, acidosis, or alkalosis.

168. What are the two primary classifications of an ABG problem?  
Respiratory-related or metabolic-related.

169. Which parameter represents the respiratory component of an ABG?  
PaCO₂.

170. Which parameter represents the metabolic component of an ABG?  
HCO₃.

171. What happens to pH when H+ ion concentration increases?  
The pH decreases, leading to acidosis (pH < 7.35).

172. What happens to pH when H+ ion concentration decreases?  
The pH increases, leading to alkalosis (pH > 7.45).

173. Below what pH level does a patient typically require intubation?  
A pH below 7.20 usually indicates the need for intubation.

174. If the pH and PaCO₂ move in opposite directions, what does this indicate?  
A respiratory problem.

175. If the pH and HCO₃ move in the same direction, what does this indicate?  
A metabolic problem.

176. What type of compensation is indicated when the pH, PaCO₂, and HCO₃ are all out of range?
Partially compensated.

177. What type of compensation is indicated when the pH is out of range but either the PaCO₂ or HCO₃ is still normal?  
Uncompensated.

178. What type of compensation is indicated when the pH is normal, but the PaCO₂ and HCO₃ are out of range?  
Fully compensated.

179. What does the SaO₂ measure?  
It measures the percentage of hemoglobin that is saturated with oxygen in arterial blood.

180. What two devices are used to accurately measure MetHb and COHb levels?  
An ABG analyzer and a co-oximeter.

181. What are the most important values to examine when analyzing an ABG?  
The patient’s ventilation status (PaCO₂) and oxygenation status (PaO₂).

182. How is ventilation assessed?  
By measuring the PaCO₂ level.

183. How is oxygenation assessed?  
By measuring the PaO₂ level.

184. What two electrochemical oxygen analyzers are commonly used for FiO₂ monitoring?  
The Clark electrode and the galvanic cell.

185. Where can blood gas samples be obtained from?  
Peripheral arteries, indwelling arterial catheters, or capillary sampling.

186. What is considered the gold standard for assessing gas exchange?  
Arterial Blood Gases (ABGs).

187. Why is the radial artery the preferred site for arterial blood sampling?  
It is near the surface, easy to palpate and stabilize, has good collateral circulation from the ulnar artery, is not close to large veins, and generally causes less pain (although patients may disagree!).

188. What are the primary indications for obtaining an ABG?  
To evaluate ventilation, acid-base balance, oxygenation status, and oxygen-carrying capacity of the blood; to assess a patient’s response to therapy or diagnostic tests; and to monitor the severity and progression of a documented disease.

189. What can cause errors in an ABG sample?  
Air bubbles in the sample, venous admixture, excess anticoagulant, and metabolic changes if the sample is not analyzed promptly.

190. How soon should an ABG sample be analyzed?  
Within 15 minutes to ensure accuracy.

191. What are some potential hazards and complications of ABG sampling?  
Bleeding, hematoma, infection, air or blood embolism, arterial spasm, vessel occlusion, ischemia or necrosis distal to the puncture site.

192. What test should be performed on a patient who survived a house fire?  
An ABG with co-oximetry to assess carbon monoxide levels (COHb).

193. What is a quick method to estimate whether a patient is well-oxygenated based on their PaO₂?  
Use the rule of thumb: PaO₂ ≈ 5 × FiO₂.

194. What are the four main values to assess when interpreting an ABG?  
pH, PaCO₂, HCO₃, and Base Excess (BE).

195. How would you describe an ABG in simple terms?  
It is a fundamental diagnostic tool used to assess oxygenation (PaO₂) and acid-base balance (pH and PaCO₂) in patients.

196. What are normal results for a positive Modified Allen test?  
The hand should flush pink within 5-7 seconds after releasing ulnar artery pressure.

197. What are some alternative methods for checking collateral blood flow?  
Doppler ultrasound and pulse oximetry.

198. What are the contraindications for obtaining an ABG?  
A negative Allen test, presence of a lesion or vascular graft at the site, or a site distal to a surgical shunt (e.g., dialysis patients); caution should be used with patients on anticoagulants.

199. Why is the radial artery preferred for ABG sampling?  
It is superficial, easy to palpate and stabilize, has collateral circulation, is not near large veins, and is generally well-tolerated (though not always pain-free!).

200. What parameters does a blood gas analyzer directly measure?  
pH (Sanz electrode), PaCO₂ (Severinghaus electrode), and PaO₂ (Clark electrode).

Final Thoughts

Mastering arterial blood gas (ABG) interpretation is essential for diagnosing and managing respiratory and metabolic disorders. By practicing these questions, healthcare professionals can strengthen their understanding of acid-base imbalances, oxygenation, and proper sampling techniques.

Whether you’re preparing for an exam or refining your clinical decision-making skills, a strong grasp of ABG analysis will enhance your ability to provide effective patient care. Keep reviewing and practicing to build confidence in interpreting ABG results accurately.