ABGs

Question 1

What PaO₂ value is generally considered indicative of respiratory failure?

A. <10 kPa
B. <8 kPa
C. <12 kPa
D. <6 kPa

Answer 1

B

Question 2

Type I respiratory failure is characterised by:

A. Low PaO₂ with high PaCO₂
B. Low PaO₂ with normal or low PaCO₂
C. High PaO₂ and low PaCO₂
D. High PaO₂ with high PaCO₂

Answer 2

B

Question 3

Type II respiratory failure is characterised by:

A. Low PaO₂ and high PaCO₂
B. Low PaO₂ and low PaCO₂
C. Normal PaO₂ and low PaCO₂
D. High PaO₂ and normal PaCO₂

Answer 3

A

Question 4

Acute respiratory failure often presents with:

A. Fully compensated pH
B. Low pH due to lack of renal compensation
C. High bicarbonate levels
D. Low PaCO₂ with alkalosis

Answer 4

B

Question 5

Chronic respiratory failure may show:

A. High pH with no change in PaCO₂
B. Normal or slightly low pH due to renal compensation
C. Low bicarbonate and low pH
D. Rapid changes in oxygenation only

Answer 5

B

Question 6

The most accurate method to obtain ABG measurements is:

A. Capillary blood gas (CBG)
B. Venous blood gas (VBG)
C. Arterial stab or arterial line
D. Pulse oximetry

Answer 6

C

Question 7

Which of the following is NOT a primary purpose of ABG analysis?

A. Identify respiratory failure
B. Monitor deterioration or improvement
C. Diagnose diabetes
D. Guide oxygen therapy or ventilatory support

Answer 7

C

Question 8

Hypercapnia is defined as:

A. PaCO₂ <4.7 kPa
B. PaCO₂ >6 kPa
C. PaO₂ <8 kPa
D. HCO₃⁻ >28 mmol/L

Answer 8

B

Question 9

Hypocapnia is defined as:

A. PaCO₂ <4.7 kPa
B. PaCO₂ >6 kPa
C. PaO₂ <8 kPa
D. BE > +2

Answer 9

A

Question 10

Respiratory acidosis is characterised by:

A. Low PaCO₂ and high pH
B. High PaCO₂ and low pH
C. Low PaCO₂ and low HCO₃⁻
D. High HCO₃⁻ only

Answer 10

B

Question 11

Metabolic alkalosis is suggested by:

A. pH <7.35, HCO₃⁻ <22 mmol/L
B. pH >7.45, HCO₃⁻ >26 mmol/L
C. pH <7.35, PaCO₂ >6 kPa
D. pH >7.45, PaCO₂ <4.7 kPa

Answer 11

B

Question 12

Base excess (BE) is:

A. Direct measure of PaCO₂
B. A measure of bicarbonate deviation from normal
C. Same as PaO₂
D. Only important in hypoxaemia

Answer 12

B

Question 13

Full compensation in ABGs occurs when:

A. PaCO₂ and HCO₃⁻ are normal, pH is abnormal
B. PaCO₂ and HCO₃⁻ are out of normal range, pH within normal limits
C. Only pH is abnormal
D. Only PaO₂ is low

Answer 13

B

Question 14

Partial compensation occurs when:

A. pH is fully normal
B. PaCO₂ and HCO₃⁻ both abnormal, pH not fully normal
C. Only bicarbonate is abnormal
D. Oxygenation is reduced

Answer 14

B

Question 15

Oxygenation (PaO₂) is important to check because:

A. It directly affects pH
B. It indicates oxygen transfer efficiency from lungs to blood
C. It measures bicarbonate buffering
D. It determines PaCO₂

Answer 15

B

Question 16

When interpreting ABGs, the first step is:

A. Check PaO₂
B. Check HCO₃⁻
C. Check pH
D. Check base excess

Answer 16

C

Question 17

In a respiratory problem, pH and PaCO₂ typically:

A. Move in opposite directions
B. Move in the same direction
C. Remain unchanged
D. Only PaO₂ changes

Answer 17

A

Question 18

In a metabolic problem, pH and HCO₃⁻ typically:

A. Move in opposite directions
B. Move in the same direction
C. Only PaO₂ changes
D. Only PaCO₂ changes

Answer 18

B

Question 19

Renal compensation for acidosis:

A. Starts within 1–3 minutes
B. Retains HCO₃⁻ to increase pH
C. Excretes CO₂
D. Reduces oxygen delivery

Answer 19

B

Question 20

Henderson-Hasselbalch equation relates:

A. H⁺, HCO₃⁻, and PaO₂
B. H⁺, HCO₃⁻, and H₂CO₃
C. HCO₃⁻ and PaO₂ only
D. pH and SaO₂ only

Answer 20

B

Question 21

Acute respiratory failure is less likely to have:

A. Low pH
B. Compensatory raised HCO₃⁻
C. Low PaO₂
D. Hypercapnia (if type II)

Answer 21

B

Question 22

Converting ABG values from kPa to mmHg involves:

A. Multiply by 7.5
B. Divide by 7.5
C. Multiply by 10
D. Divide by 10

Answer 22

A

Question 23

Type II respiratory failure often requires:

A. No oxygen therapy
B. Controlled oxygen ± mechanical ventilation
C. Only physiotherapy
D. Diuretics

Answer 23

B

Question 24

A patient’s ABG shows low PaO₂ with normal PaCO₂. Ventilation appears to be compensating. Which best describes this pattern?
A. Type I respiratory failure with V/Q mismatch or diffusion limitation
B. Type II respiratory failure with ventilatory failure
C. Compensated metabolic acidosis
D. Acute respiratory alkalosis

Answer 24

A

Question 25

When converting a blood gas value from mmHg to kPa, which operation is correct? A. Multiply by 7.5 B. Divide by 7.5 C. Multiply by 0.75 D. Divide by 0.133

Answer 25

B

Question 26

A patient on 60% FiO₂ has a PaO₂ of 10.7 kPa. How should this result be interpreted? A. Normal — PaO₂ of 10.7 kPa is always acceptable B. Borderline — requires clinical correlation only C. Abnormal — PaO₂ should be much higher given the high FiO₂ being delivered D. Cannot be interpreted without the SaO₂ value

Answer 26

C

Question 27

In a respiratory acid-base disturbance, which relationship between pH and PaCO₂ is expected? A. Both rise together B. Both fall together C. They move in the same direction D. They move in opposite directions (seesaw)

Answer 27

D

Question 28

Which of the following is considered the most accurate method for obtaining measurements of arterial oxygen and carbon dioxide? A. Arterial stab (direct arterial puncture) B. Venous blood gas (VBG) C. Capillary blood gas (CBG) D. Pulse oximetry with end-tidal CO₂ monitoring

Answer 28

A

Question 29

A patient has pH 7.28, HCO₃⁻ 14 mmol/L, and BE −8. What is the primary disturbance? A. Respiratory acidosis B. Metabolic acidosis C. Compensated metabolic alkalosis D. Mixed respiratory and metabolic alkalosis

Answer 29

B

Question 30

Renal compensation for respiratory acidosis involves which mechanism? A. Increasing alveolar ventilation to blow off CO₂ B. Excreting more HCO₃⁻ in the urine C. Retaining HCO₃⁻ to raise blood alkalinity and restore pH D. Releasing H⁺ ions into the bloodstream

Answer 30

C

Question 31

What does 'full compensation' mean in ABG interpretation? A. Only pH is abnormal; both PaCO₂ and HCO₃⁻ are within normal range B. All ABG values including pH are within normal limits C. pH is within normal range but both PaCO₂ and HCO₃⁻ remain outside normal limits D. PaCO₂ is normal but HCO₃⁻ remains abnormal

Answer 31

C

Question 32

Type II respiratory failure is distinguished from Type I by which feature? A. PaO₂ is low and PaCO₂ is normal or low B. It only occurs in patients with chronic lung disease C. It requires no supplemental oxygen therapy D. PaO₂ is low AND PaCO₂ is elevated, indicating ventilatory failure

Answer 32

D

Question 33

How quickly does the respiratory buffer system begin to compensate for an acid-base imbalance? A. Within 1–3 minutes B. Within 1–3 hours C. Within 6–12 hours D. Within 1–3 days

Answer 33

A

Question 34

A patient has pH 7.5, HCO₃⁻ 30 mmol/L, and BE +8. What is the diagnosis? A. Respiratory alkalosis B. Metabolic alkalosis C. Partially compensated respiratory acidosis D. Fully compensated metabolic acidosis

Answer 34

B

Question 35

Which buffering system uses haemoglobin and plasma proteins to minimise pH changes? A. Carbonic acid-bicarbonate system B. Phosphate system C. Protein system D. Renal bicarbonate system

Answer 35

C

Question 36

What is the threshold for diagnosing hypercapnia on an ABG? A. PaCO₂ > 8 kPa B. PaCO₂ > 7 kPa C. PaCO₂ > 5.5 kPa D. PaCO₂ > 6 kPa

Answer 36

D

Question 37

In acute respiratory failure, why is the pH typically low despite the body's buffering systems? A. The kidneys immediately excrete HCO₃⁻, worsening acidosis B. Haemoglobin is saturated and cannot buffer further C. The carbonic acid-bicarbonate ratio is always disrupted in acute disease D. There is little to no HCO₃⁻ compensation as renal compensation takes days to develop

Answer 37

D

Question 38

Which statement correctly describes the role of PaO₂ in acid-base interpretation? A. PaO₂ directly determines blood pH through its effect on carbonic acid B. PaO₂ reflects dissolved oxygen and has no direct effect on pH or acid-base status C. A low PaO₂ always indicates metabolic acidosis D. PaO₂ and SaO₂ are interchangeable measures in acid-base assessment

Answer 38

B

Question 39

A patient with known COPD has raised HCO₃⁻ and a near-normal pH. What is the most likely explanation? A. The patient has an acute metabolic alkalosis unrelated to their lung disease B. Compensated respiratory acidosis — the kidneys have retained HCO₃⁻ over time to normalise pH C. The raised HCO₃⁻ indicates the patient is receiving excessive oxygen therapy D. The near-normal pH means there is no underlying acid-base disorder

Answer 39

B

Question 40

In metabolic acid-base problems, which relationship between pH and HCO₃⁻ applies? A. pH and HCO₃⁻ move in opposite directions B. pH falls while HCO₃⁻ remains unchanged C. pH and HCO₃⁻ move in the same direction D. HCO₃⁻ changes but pH is unaffected

Answer 40

C

Question 41

What does base excess (BE) indicate clinically? A. The amount of additional CO₂ the lungs must excrete B. The total oxygen-carrying capacity of haemoglobin C. How much HCO₃⁻ is above or below the average of 24 mmol/L — indicating what would theoretically correct pH D. The pH correction factor applied when the patient's temperature deviates from normal

Answer 41

C

Question 42

Why might it be impossible to distinguish compensated respiratory acidosis from compensated metabolic alkalosis on ABG values alone? A. Both conditions produce identical pH, PaCO₂, and PaO₂ values B. Compensation always restores all ABG values to normal, leaving no trace C. The two conditions require the same treatment so differentiation is unnecessary D. Both show elevated HCO₃⁻ with near-normal pH — clinical context or serial ABGs are needed to differentiate

Answer 42

D

Question 43

Which ABG pattern describes a respiratory alkalosis? A. pH 7.20, PaCO₂ 8.3 kPa, PaO₂ 8.4 kPa B. pH 7.49, PaCO₂ 4.2 kPa, PaO₂ 15 kPa C. pH 7.28, HCO₃⁻ 14 mmol/L, BE −8 D. pH 7.50, HCO₃⁻ 30 mmol/L, BE +8

Answer 43

B