Respiratory System Practice Questions

Q: A 32-year-old woman develops acute respiratory distress syndrome (ARDS) following sepsis. She is mechanically ventilated with tidal volume 450 mL and plateau pressure 35 cm H2O (PEEP 10 cm H2O). Her static compliance is calculated as 18 mL/cm H2O. The team considers changing ventilator settings. Analyzing her respiratory mechanics, what change would most effectively improve compliance while minimizing ventilator-induced lung injury?

Increase PEEP to 15 cm H2O to prevent alveolar collapse. ***Increase PEEP to 15 cm H2O to prevent alveolar collapse*** - In **ARDS**, static compliance is low due to widespread **alveolar collapse**; increasing **PEEP** (Positive End-Expiratory Pressure) recruits collapsed alveoli and shifts the lung to a more compliant part of the **pressure-volume curve**. - Preventing cyclic collapse (atelectrauma) through adequate PEEP minimizes **Ventilator-Induced Lung Injury (VILI)** while effectively improving gas exchange area and lung mechanics. *Increase tidal volume to 600 mL to recruit more alveoli* - High tidal volumes increase the risk of **volutrauma** and **overdistension** of relatively healthy alveoli (the "baby lung" concept in ARDS). - This action would likely increase the **plateau pressure** further above the 30 cm H2O safety threshold, worsening lung injury. *Decrease PEEP to 5 cm H2O to reduce plateau pressure* - Reducing PEEP below the **lower inflection point** leads to **atelectrauma** via the repeated opening and closing of unstable alveoli. - While it might lower peak pressures, it would cause a drop in functional residual capacity and a significant decrease in **static compliance**. *Switch to pressure-control mode with same plateau pressure* - Simply switching to **pressure-control ventilation** does not inherently change the underlying **respiratory mechanics** or lung compliance if the plateau pressure remains constant. - Without addressing alveolar recruitment through PEEP, the **compliance** remains compromised by the disease process itself. *Increase respiratory rate while maintaining current tidal volume* - Increasing the **respiratory rate** may help manage hypercapnia but does not directly improve the **static compliance** of the lung tissue. - High rates can lead to **auto-PEEP** or intrinsic PEEP, which can complicate the assessment of plateau pressures and hemodynamics.

Question 1

A 68-year-old man with both severe COPD (emphysema) and newly diagnosed idiopathic pulmonary fibrosis presents with worsening dyspnea. His pressure-volume curve shows a complex pattern with features of both diseases. Static compliance measured at mid-lung volumes is 120 mL/cm H2O. His pulmonologist must decide on optimal management. Synthesizing the pathophysiology of both conditions, what represents the most significant clinical challenge in managing his combined disease?

Accepted Answer

The opposing effects on compliance create a pseudonormal total respiratory compliance masking disease severity

Answer

Emphysema treatment with bronchodilators will worsen fibrosis progression

Answer

Pulmonary rehabilitation cannot address the opposing mechanical derangements

Answer

The increased compliance from emphysema completely negates decreased compliance from fibrosis

Answer

Oxygen therapy beneficial for COPD will accelerate fibrotic changes

Question 2

A 42-year-old woman with systemic sclerosis develops both pulmonary fibrosis and chest wall restriction from skin thickening. Her measured total respiratory system compliance is 30 mL/cm H2O. Testing with complete paralysis and positive pressure ventilation shows isolated lung compliance of 50 mL/cm H2O. She is being considered for immunosuppressive therapy versus supportive care. Evaluate which intervention would provide the greatest improvement in her respiratory mechanics.

Accepted Answer

Combined therapy targeting lung disease with chest wall mobilization

Answer

Aggressive immunosuppression targeting both lung and skin disease

Answer

Lung-directed therapy only, as it contributes more to total compliance reduction

Answer

Supportive care only, as both components contribute equally and irreversibly

Answer

Chest wall-directed physical therapy, as it is the primary limiting factor

Question 3

A 58-year-old man with end-stage pulmonary fibrosis is being evaluated for lung transplantation. His current static compliance is 25 mL/cm H2O (normal: 200 mL/cm H2O). He also has mild obesity (BMI 32) and ankylosing spondylitis affecting chest wall mobility. Post-transplant, assuming successful bilateral lung transplant with normal donor lungs, what would be the expected change in his total respiratory system compliance?

Accepted Answer

Improved but still reduced compliance due to persistent chest wall restriction

Answer

Return to completely normal respiratory compliance matching healthy individuals

Answer

Improved lung compliance but worsened chest wall compliance from surgery

Answer

Worse compliance initially due to transplant rejection and denervation

Answer

No significant change because the primary problem is muscular weakness

Question 4

A research study compares two patients with different lung pathologies but identical functional residual capacity (FRC) of 3.0 L. Patient A has pulmonary fibrosis with FRC above the steep portion of the compliance curve. Patient B has emphysema with FRC on the flat upper portion of the curve. Both attempt to inhale the same tidal volume. Analyzing their work of breathing, which statement best characterizes the difference?

Accepted Answer

Patient B does more elastic work due to hyperinflation beyond optimal compliance

Answer

Patient A does more elastic work; Patient B does more resistive work

Answer

Patient B does less work because emphysematous lungs are more compliant

Answer

Patient A does less work because fibrotic lungs have increased elastic recoil assisting inspiration

Answer

Both do equal work because FRC and tidal volumes are identical

Question 5

A 32-year-old woman develops acute respiratory distress syndrome (ARDS) following sepsis. She is mechanically ventilated with tidal volume 450 mL and plateau pressure 35 cm H2O (PEEP 10 cm H2O). Her static compliance is calculated as 18 mL/cm H2O. The team considers changing ventilator settings. Analyzing her respiratory mechanics, what change would most effectively improve compliance while minimizing ventilator-induced lung injury?

Accepted Answer

Increase PEEP to 15 cm H2O to prevent alveolar collapse

Answer

Increase tidal volume to 600 mL to recruit more alveoli

Answer

Decrease PEEP to 5 cm H2O to reduce plateau pressure

Answer

Switch to pressure-control mode with same plateau pressure

Answer

Increase respiratory rate while maintaining current tidal volume

Respiratory System — MCQs

Respiratory System — MCQs

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