Q:1
A 4-year-old with severe pneumonia is intubated. Despite FiO₂ 1.0 and adequate ventilation (PaCO₂ 40 mmHg), PaO₂ remains 55 mmHg. Chest X-ray shows bilateral consolidation. What is the primary mechanism of hypoxemia?
A. Alveolar hypoventilation
B. Diffusion limitation
C. Intrapulmonary shunt
D. Increased dead space
E. Low inspired oxygen fraction
Answer:
C
Explanation:
Refractory hypoxemia despite high FiO₂ indicates shunt physiology, blood passing through non-ventilated alveoli. Oxygen therapy has limited effect in true shunt states.
Q:2
A ventilated child with severe asthma has rising PaCO₂ despite high minute ventilation. Capnography shows low end-tidal CO₂ compared with PaCO₂. What explains this gradient?
A. Increased shunt
B. Increased physiological dead space
C. Hypoventilation
D. Diffusion defect
E. Decreased CO₂ production
Answer:
B
Explanation:
Increased PaCO₂–ETCO₂ gradient reflects increased dead space. In asthma, airflow obstruction and uneven ventilation increase physiologic dead space.
Q:3
A 6-year-old with ARDS is ventilated in volume control mode. Plateau pressure is 32 cmH₂O, PEEP 12 cmH₂O, tidal volume 6 mL/kg. What does this indicate?
A. High airway resistance
B. Low lung compliance
C. Auto-PEEP
D. Air leak
E. Hyperinflation
Answer:
B
Explanation
Driving pressure = Plateau − PEEP = 20 cmH₂O (elevated), indicating reduced respiratory system compliance consistent with ARDS.
Q:4
A child with status asthmaticus has a peak inspiratory pressure (PIP) of 40 cmH₂O and a plateau pressure of 18 cmH₂O. What is the dominant abnormality?
A. Decreased compliance
B. Increased airway resistance
C. Low tidal volume
D. High PEEP
E. Pulmonary oedema
Answer:
B
Explanation:
A large difference between PIP and plateau pressure indicates elevated airway resistance. Compliance is reflected by plateau pressure, which is normal here.
Q:5
A 5-year-old with ARDS has PaCO₂ 60 mmHg and pH 7.28 while on lung-protective ventilation (VT 6 mL/kg). What is the rationale for tolerating this?
A. Prevent oxygen toxicity
B. Avoid barotrauma and volutrauma
C. Improve CO₂ clearance
D. Reduce sedation needs
E. Increase pulmonary blood flow
Answer:
B
Explanation:
Permissive hypercapnia allows low tidal volumes to minimise ventilator-induced lung injury. Mild acidosis is tolerated to protect the lung parenchyma.
Q:6
A ventilated asthmatic child becomes hypotensive. The flow-time waveform shows that expiratory flow does not return to baseline before the next breath. What is the most likely mechanism?
A. Hypovolemia
B. Increased intrathoracic pressure from auto-PEEP
C. Tension pneumothorax
D. Myocardial depression
E. Anaphylaxis
Answer:
B
Explanation:
Incomplete exhalation causes dynamic hyperinflation (auto-PEEP), increasing intrathoracic pressure, reducing venous return, and causing hypotension.
Q:7
A child with severe ARDS has: FiO₂ 0.9, Mean airway pressure 22 cmH₂O, PaO₂ 60 mmHg. What is the oxygenation index?
A. 15
B. 22
C. 30
D. 33
E. 45
Answer:
D
Explanation:
OI = (FiO₂ × MAP × 100) / PaO₂ = (0.9 × 22 × 100) / 60 = 33
OI >16–25 indicates severe disease; >40 is often considered for ECMO.
Q:8
A child with ARDS is transitioned to APRV. Oxygenation improves without increasing FiO₂. What is the primary mechanism?
A. Increased dead space
B. Reduced cardiac output
C. Increased mean airway pressure and alveolar recruitment
D. Decreased CO₂ production
E. Increased airway resistance
Answer:
C
Explanation:
APRV maintains prolonged high airway pressure, increasing mean airway pressure and promoting alveolar recruitment, improving oxygenation.
Q:9
A ventilated child develops sudden hypoxemia. Breath sounds are equal, CXR is normal, and ETCO₂ decreases abruptly. Most likely diagnosis?
A. Pneumonia progression
B. Pulmonary embolism
C. Atelectasis
D. ARDS worsening
E. Bronchospasm
Answer:
B
Explanation:
Sudden hypoxemia with a drop in ETCO₂ and a normal CXR suggests an acute increase in dead space, as seen in pulmonary embolism.
Q:10
In ARDS management, which parameter is most associated with mortality?
A. FiO₂ level
B. Peak inspiratory pressure
C. Driving pressure (Plateau − PEEP)
D. Respiratory rate
E. ETCO₂
Answer:
C
Explanation:
Driving pressure correlates strongly with mortality in ARDS. It reflects dynamic strain on the lung and is a key target in lung-protective ventilation.
