Respiratory Failure — MCQs

10 questions

Which of the following laboratory findings is most consistent with hypoxia due to acute respiratory distress syndrome (ARDS)?

Which of the following is the common cause of respiratory failure type 2 ?

A patient with acute pulmonary embolism is found to have hypoxia. What is the most likely mechanism causing hypoxia in this condition?

Which of the following conditions is a common cause of hypoxia with a normal A-a gradient?

Blood gas measurements of a patient show the following values: pH 7.2, pCO2 80 mm Hg, and pO2 46 mm Hg. Which of the following could be the most probable diagnosis?

In conventional oxygen therapy, which device will deliver the highest FiO2?

Which of the following statements is true regarding the diagnostic criteria for Chronic Obstructive Pulmonary Disease (COPD)?

A known case of COPD with acute exacerbation of symptoms. On examination patient was conscious and alert, pulse was 110 beats/ min and bilateral wheeze present. All of the following are true in the management of the patient except:

A hyperventilating patient has the following ABG values: pH=7.53, pCO2=20 mmHg, HCO3= 26 mEq/L. What is the most likely diagnosis?

Q10

Oxygen therapy may not be useful in

Respiratory Failure Indian Medical PG Practice Questions and MCQs

Question 1: Which of the following laboratory findings is most consistent with hypoxia due to acute respiratory distress syndrome (ARDS)?

A. Increased PaCO2 with decreased pH
B. Increased A-a gradient (Correct Answer)
C. Decreased PaO2 with normal PaCO2
D. Normal A-a gradient

Explanation: ***Increased A-a gradient*** - In ARDS, the **lung pathology** (e.g., alveolar edema, collapse, or consolidation) impairs gas exchange, leading to a significant **mismatch between ventilation and perfusion**. - This mismatch results in a larger-than-normal difference between the alveolar oxygen partial pressure (PAO2) and the arterial oxygen partial pressure (PaO2), which is measured as an **increased A-a gradient**. *Increased PaCO2 with decreased pH* - This finding describes **respiratory acidosis**, which would typically occur in severe **hypoventilation** or end-stage ARDS with respiratory failure. - In initial or moderate ARDS, patients often compensate with **hyperventilation** due to hypoxia, leading to decreased or normal PaCO2. *Decreased PaO2 with normal PaCO2* - While a decreased PaO2 is characteristic of hypoxia in ARDS, a **normal PaCO2** in the presence of significant hypoxemia still implies an impairment in gas exchange that would manifest as an increased A-a gradient. - This specific combination (decreased PaO2, normal PaCO2) is not as specific as the A-a gradient for identifying the underlying cause of hypoxia due to shunt or V/Q mismatch. *Normal A-a gradient* - A normal A-a gradient suggests that **gas exchange in the lungs is efficient**, and any hypoxia is likely due to **hypoventilation** or **low inspired oxygen**. - This finding would rule out significant intrinsic lung disease, such as ARDS, as the primary cause of hypoxia.

Question 2: Which of the following is the common cause of respiratory failure type 2 ?

A. Chronic bronchitis exacerbation (Correct Answer)
B. Acute attack asthma
C. ARDS
D. Pneumonia

Explanation: ***Chronic bronchitis exacerbation*** - **Chronic bronchitis** is a common cause of **Type 2 respiratory failure**, characterized by **hypercapnia** (elevated CO2) due to impaired alveolar ventilation [1]. - An exacerbation worsens **airflow obstruction** and leads to increased work of breathing and CO2 retention [1]. *Acute attack asthma* - While severe asthma can cause respiratory failure, it typically presents initially as **Type 1 (hypoxemic)**, with severe bronchospasm and V/Q mismatch [2]. - **Hypercapnia** in asthma is a sign of **severe, impending respiratory collapse** rather than the primary cause of respiratory failure. *ARDS* - **Acute Respiratory Distress Syndrome (ARDS)** is a classic cause of **Type 1 (hypoxemic) respiratory failure**, characterized by widespread inflammation and fluid accumulation in the lungs [2]. - ARDS primarily involves impaired oxygenation rather than CO2 elimination issues, unless it progresses to severe stages with significant muscle fatigue. *Pneumonia* - **Pneumonia** predominantly causes **Type 1 (hypoxemic) respiratory failure** due to consolidation and V/Q mismatch in affected lung areas, leading to impaired oxygen diffusion [2]. - While severe, widespread pneumonia can eventually lead to ventilatory failure, its initial and primary impact is on oxygenation.

Question 3: A patient with acute pulmonary embolism is found to have hypoxia. What is the most likely mechanism causing hypoxia in this condition?

A. Hypoventilation
B. Diffusion impairment
C. Ventilation-perfusion mismatch (Correct Answer)
D. Shunt

Explanation: ***Ventilation-perfusion mismatch*** - A pulmonary embolism blocks blood flow to a portion of the lung, creating areas that are **ventilated but not perfused** (increased dead space with high V/Q ratio). - Blood is redirected to the remaining perfused lung areas, which then become relatively **overperfused** (low V/Q ratio), impairing efficient oxygen uptake. - This V/Q mismatch—with both high V/Q (dead space) and low V/Q (relative shunt) areas—leads to **hypoxemia**, making it the **most common mechanism** of hypoxia in acute PE. *Hypoventilation* - This condition involves a generalized decrease in alveolar ventilation, leading to **hypercapnia** (increased CO2) and hypoxemia. - While PE can cause shortness of breath and tachypnea, the primary mechanism of hypoxia is not due to overall reduced ventilation, but rather disrupted matching of ventilation to perfusion. *Diffusion impairment* - Diffusion impairment occurs when the alveolar-capillary membrane is compromised, preventing proper oxygen transfer, as seen in conditions like **pulmonary fibrosis** or **interstitial lung disease**. - Pulmonary embolism primarily affects **blood flow distribution**, not the structural integrity or diffusion capacity of the alveolar-capillary membrane. *Shunt* - A true shunt occurs when deoxygenated blood bypasses ventilated alveoli entirely and enters systemic circulation, as seen in **intracardiac defects** or severe **ARDS**. - While massive PE can rarely lead to right-to-left shunting through a patent foramen ovale (due to increased right heart pressure), the **primary and most common mechanism** of hypoxia in typical acute PE is V/Q mismatch, not shunt.

Question 4: Which of the following conditions is a common cause of hypoxia with a normal A-a gradient?

A. Pulmonary fibrosis
B. Pulmonary embolism
C. Pneumonia
D. Hypoventilation (Correct Answer)

Explanation: ***Hypoventilation*** - **Hypoventilation** reduces the partial pressure of oxygen in the alveoli (PAO2) due to inadequate ventilation, leading to decreased arterial oxygen tension (PaO2). - The **A-a gradient** remains normal because both PAO2 and PaO2 decrease proportionally, maintaining their normal difference. *Pulmonary fibrosis* - **Pulmonary fibrosis** causes hypoxia primarily due to impaired diffusion and V/Q mismatch. - This leads to a **widened A-a gradient** as oxygen transfer from alveoli to blood is compromised. *Pulmonary embolism* - A **pulmonary embolism** causes hypoxia due to V/Q mismatch, specifically creating dead space (ventilated but not perfused alveoli). - This results in an **increased A-a gradient** because the inefficiency of gas exchange elevates the difference between alveolar and arterial oxygen. *Pneumonia* - **Pneumonia** causes hypoxia due to accumulation of fluid and inflammatory cells in the alveoli, leading to V/Q mismatch and sometimes shunting. - This pathology results in a **widened A-a gradient** because the effective diffusion of oxygen from affected alveoli into the capillaries is impaired.

Question 5: Blood gas measurements of a patient show the following values: pH 7.2, pCO2 80 mm Hg, and pO2 46 mm Hg. Which of the following could be the most probable diagnosis?

A. Acute exacerbation of COPD (Correct Answer)
B. Acute bronchospasm
C. Pulmonary embolism
D. Chronic pneumonia

Explanation: ***Acute exacerbation of COPD*** - The patient presents with **respiratory acidosis** (pH 7.2, normal 7.35-7.45) and **hypercapnia** (pCO2 80 mm Hg, normal 35-45 mm Hg), combined with severe **hypoxemia** (pO2 46 mm Hg, normal 80-100 mm Hg) [2]. - This pattern is highly indicative of an acute exacerbation of **Chronic Obstructive Pulmonary Disease**, where worsening airflow obstruction leads to inadequate alveolar ventilation and impaired gas exchange; clinical evidence suggests long-term oxygen therapy can decrease mortality in these chronic patients [1]. *Acute bronchospasm* - While acute bronchospasm can cause hypoxemia and hypercapnia, the degree of hypercapnia (pCO2 80 mm Hg) seen here is typically more severe and prolonged than commonly observed in isolated bronchospasm. Indications for assisted ventilation in severe asthma include a rising PaCO2 above 45 mmHg [3]. - Acute bronchospasm would likely result in less pronounced acidosis and more rapid response to bronchodilator therapy, which isn't described. *Pulmonary embolism* - Pulmonary embolism typically causes **hypoxemia** and **hypocapnia** (low pCO2) due to reflex hyperventilation in response to V/Q mismatch, which contradicts the presented blood gas values [2]. - The primary defect in pulmonary embolism is an obstruction of blood flow, not a global ventilation impairment leading to severe hypercapnia. *Chronic pneumonia* - Chronic pneumonia can cause **hypoxemia** due to V/Q mismatch or shunting, but it generally leads to **hypocapnia** or normal pCO2 if the patient is able to compensate by increasing ventilation [2]. - Severe hypercapnia (pCO2 80 mm Hg) with acute acidosis is less typical for uncomplicated chronic pneumonia, unless it's a very advanced or acute severe presentation with respiratory muscle fatigue.

Question 6: In conventional oxygen therapy, which device will deliver the highest FiO2?

A. Hudson mask
B. Venturi mask
C. Non rebreathing mask (Correct Answer)
D. Nasal cannula

Explanation: **Non rebreathing mask** - This device features a **one-way valve** between the mask and the reservoir bag, preventing exhaled air from mixing with fresh oxygen. This allows for the delivery of the **highest possible FiO2** among conventional oxygen therapy devices, often up to 90-100%. - The **reservoir bag** ensures a continuous supply of high-concentration oxygen during inspiration, maximizing the amount of oxygen inhaled. *Hudson mask* - Also known as a **simple face mask**, it delivers a moderate FiO2 (40-60%) at flow rates of 5-10 L/min. - The open ports on the sides allow for mixing of room air with oxygen, making it less efficient for delivering very high oxygen concentrations. *Venturi mask* - This device uses the Venturi principle to deliver a **precise and consistent FiO2** by entraining room air with oxygen. - While it provides controlled oxygen delivery, its maximum FiO2 typically ranges from 24-60%, which is lower than a non-rebreathing mask. *Nasal cannula* - The nasal cannula delivers a relatively low FiO2 (24-44%) at flow rates of 1-6 L/min. - It is designed for **low-flow oxygen delivery** and is not suitable for patients requiring high concentrations of oxygen.

Question 7: Which of the following statements is true regarding the diagnostic criteria for Chronic Obstructive Pulmonary Disease (COPD)?

A. A post-bronchodilator FEV1/FVC ratio above the threshold indicates normal lung function.
B. A post-bronchodilator FEV1/FVC ratio below the threshold indicates airflow limitation. (Correct Answer)
C. Residual Volume (RV) is normal.
D. Total Lung Capacity (TLC) is decreased.

Explanation: ***A post-bronchodilator FEV1/FVC ratio below the threshold indicates airflow limitation.*** [1] - This is the **hallmark diagnostic criterion** for COPD, confirming persistent **airflow obstruction** that is not fully reversible. [1] - The threshold typically used is **< 0.70** or below the **fifth percentile** of the lower limit of normal (LLN). *A post-bronchodilator FEV1/FVC ratio above the threshold indicates normal lung function.* - An FEV1/FVC ratio **above the threshold** indicates the absence of significant **airflow obstruction**, but does not automatically guarantee normal lung function as other parameters like **FEV1** could be affected. - This measurement would suggest a **restrictive lung disease** or **normal lung function**, depending on other spirometry values. *Residual Volume (RV) is normal.* - In COPD, **air trapping** due to airflow obstruction leads to an **increased Residual Volume (RV)**, not a normal RV. - An elevated RV reflects **hyperinflation** of the lungs, a characteristic feature of emphysema and chronic bronchitis. *Total Lung Capacity (TLC) is decreased.* - COPD is characterized by **hyperinflation**, which typically results in an **increased Total Lung Capacity (TLC)** as the lungs become more distended. - A **decreased TLC** would be indicative of a **restrictive lung disease**, which is different from obstructive patterns seen in COPD.

Question 8: A known case of COPD with acute exacerbation of symptoms. On examination patient was conscious and alert, pulse was 110 beats/ min and bilateral wheeze present. All of the following are true in the management of the patient except:

A. Non invasive ventilation is contraindicated (Correct Answer)
B. Permissible hypercapnia allowed
C. Inhalation with salbutamol
D. I/V steroids

Explanation: ***Non invasive ventilation is contraindicated*** - This statement is **false**, therefore the correct exception. **Non-invasive ventilation (NIV)** is often indicated and beneficial in the management of acute exacerbations of COPD, especially in patients with **respiratory acidosis** or persistent dyspnea, as it can reduce the need for intubation and improve outcomes [2]. - The patient's presentation (conscious, alert, wheeze, tachycardia) suggests an acute exacerbation, for which NIV is a key intervention unless there are absolute contraindications like cardiac arrest or inability to protect the airway [3]. *Permissible hypercapnia allowed* - **Permissive hypercapnia** is a valid strategy in managing acute exacerbations of COPD, particularly during mechanical ventilation. The goal is to maintain an adequate pH (e.g., >7.20-7.25) rather than normalizing CO2, to avoid **barotrauma** and **volutrauma** from aggressive ventilation [3]. - This approach acknowledges that some CO2 retention is acceptable as long as acidosis is not severe, protecting the lungs from excessive pressure. *Inhalation with salbutamol* - **Inhaled bronchodilators**, such as **salbutamol (a short-acting beta-agonist)**, are a cornerstone of treatment for acute COPD exacerbations [1]. They act rapidly to relieve **bronchospasm** and improve airflow, addressing the wheeze observed in the patient. - Frequent administration of these agents is crucial in the initial management to open up the airways and reduce air trapping. *I/V steroids* - **Systemic corticosteroids**, such as intravenous methylprednisolone or oral prednisone, are essential in managing acute COPD exacerbations. They reduce **airway inflammation** and swelling, leading to improved lung function and reduced recovery time. - Steroids are typically given for a short course (e.g., 5-7 days) to minimize side effects while maximizing therapeutic benefits.

Question 9: A hyperventilating patient has the following ABG values: pH=7.53, pCO2=20 mmHg, HCO3= 26 mEq/L. What is the most likely diagnosis?

A. Metabolic alkalosis
B. Metabolic acidosis
C. Respiratory alkalosis (Correct Answer)
D. Respiratory acidosis

Explanation: ***Respiratory alkalosis*** - The pH of 7.53 indicates **alkalemia**, and the low pCO2 (20 mmHg) is the primary driver, signifying **respiratory alkalosis** - A hyperventilating patient exhales more CO2, leading to a decrease in its partial pressure in the blood and a subsequent rise in pH - The HCO3 is within normal range (26 mEq/L), indicating **uncompensated respiratory alkalosis** *Metabolic alkalosis* - This would be characterized by a high pH and an elevated **HCO3**, but the HCO3 is within the normal range (26 mEq/L) - While it causes alkalemia, the primary disturbance here is respiratory, not metabolic *Metabolic acidosis* - This would present with a **low pH** and a low **HCO3**, which is contrary to the given ABG values - The patient's pH is elevated, indicating an alkalotic state, not acidotic *Respiratory acidosis* - This would be defined by a **low pH** and an elevated **pCO2**, which is the exact opposite of the provided ABG results - The patient's high pH and low pCO2 rule out respiratory acidosis

Question 10: Oxygen therapy may not be useful in

A. Pneumonia
B. Subglottic stenosis
C. Asthma
D. Pulmonary fibrosis (Correct Answer)

Explanation: **Pulmonary fibrosis** - Oxygen therapy is beneficial in **pulmonary fibrosis**, especially with exercise or at night, as it can significantly improve **oxygen saturation** and relieve **dyspnea**. - While not a cure, it improves quality of life by combating the effects of **scarring** in the lungs. *Asthma* - Oxygen therapy is a critical component in the management of **acute severe asthma** to correct **hypoxemia**. - It is often administered along with **bronchodilators** and **corticosteroids** to stabilize the patient's respiratory status. *Pneumonia* - Oxygen therapy is commonly used in pneumonia patients who develop **hypoxemia** due to impaired gas exchange in affected lung areas. - Supplemental oxygen helps maintain adequate **tissue oxygenation** and can prevent complications from severe respiratory distress. *Subglottic stenosis* - While supplemental oxygen can be administered, the primary intervention for **subglottic stenosis** often involves addressing the **airway obstruction** directly. - The benefit of oxygen therapy alone is limited due to the mechanical restriction of airflow, which may require surgical or interventional procedures.

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