A patient on mechanical ventilation has the following settings:

• FiO₂: 70%
• PEEP: 10 cm H₂O
• Tidal volume (Vt): 350 mL

These parameters are most consistent with which type of ARDS?

1. A

   Mild ARDS

2. B

   Moderate ARDS

3. C

   Severe ARDS

4. D

   Normal lung function

Appeared in: NORCET 10 Mains

Explanation

Listen in Hindi

• The Berlin Definition classifies ARDS severity by the PaO2/FiO2 ratio; Severe ARDS is defined by a ratio less than or equal to 100 mmHg.
• The provided ventilator settings, specifically a high FiO2 of 70% and a PEEP of 10 cm H2O, indicate a severe impairment in gas exchange, characteristic of severe ARDS.
• Such high support is necessary to maintain adequate oxygenation in the face of a significant intrapulmonary shunt.
• To achieve a target PaO2 of just 60 mmHg with an FiO2 of 70%, the PaO2/FiO2 ratio is approximately 86, which falls into the severe category.
• The low tidal volume (350 mL) is consistent with a lung-protective ventilation strategy used in all forms of ARDS, but it does not differentiate the severity.

Why Other Options Were Wrong

• Option A: Mild ARDS is characterized by a PaO2/FiO2 ratio between 201-300 mmHg. A patient with this level of lung injury would require much lower ventilatory support, such as a lower FiO2 (e.g., less than 50%) and lower PEEP.
• Option B: Although these settings could be seen in a deteriorating patient with moderate ARDS, the high FiO2 requirement of 70% is more indicative of a severe oxygenation defect. Typically, the need for FiO2 greater than 60% to maintain oxygenation pushes the classification towards severe ARDS.
• Option D: A person with normal lung function has no impairment in gas exchange and would not require mechanical ventilation, especially with such aggressive settings.

Related Visual

Clinical Relevance

• Nursing practice connection: Use the key finding related to Classification of Acute Respiratory Distress Syndrome (ARDS) severity based on ventilator settings to guide bedside assessment, documentation, and the next nursing action.
• Accurate ARDS classification is crucial for prognosis and guiding treatment strategies. Severe ARDS has a hospital mortality rate of approximately 46% and may require advanced therapies like prone positioning, neuromuscular blockade, or Extracorporeal Membrane Oxygenation (ECMO).
• Nurses at the bedside are responsible for implementing lung-protective ventilation strategies, monitoring for complications like barotrauma and hemodynamic instability, and assessing the patient's response to changes in FiO2 and PEEP.
• What if? If the patient's FiO2 was 40% and PEEP was 6 cm H2O, the condition would be more consistent with Mild ARDS, assuming the resulting PaO2/FiO2 ratio was between 201-300 mmHg.

How to Approach the Question

• First, identify the key clinical data provided: the patient is on mechanical ventilation for ARDS with specific settings (FiO2 70%, PEEP 10 cm H2O).
• Recall the classification system for ARDS, which is the Berlin Definition based on the PaO2/FiO2 ratio.
• Recognize that a direct calculation of the PaO2/FiO2 ratio is not possible without a PaO2 value. Therefore, the question requires you to infer the severity from the level of ventilatory support.
• Analyze the support levels. An FiO2 of 70% and a PEEP of 10 cm H2O are high levels of support, indicating a significant failure of the lungs to oxygenate the blood.
• Correlate the high level of support with the severity of the disease. A high FiO2 requirement (greater than 60%) is a strong indicator that the underlying PaO2/FiO2 ratio is likely in the severe range (less than or equal to 100 mmHg).
• Based on this inference, select 'Severe ARDS' and eliminate the other options. Mild ARDS would need less support, and Moderate ARDS is less likely given the very high FiO2.

Concept Tested & Keywords

• Concept Tested: Classification of Acute Respiratory Distress Syndrome (ARDS) severity based on ventilator settings.
• Stem keywords: mechanical ventilation, FiO2: 70%, PEEP: 10 cm H2O, ARDS
• Lead-in keywords: most consistent with
• Clinical cues: High FiO2 requirement (70%) is a key indicator of severe oxygenation failure.
• Clinical cues: High PEEP (10 cm H2O) suggests significant alveolar collapse and the need for recruitment.

Question ID

Qxf_F3ScvEeMMzKQ5uNoVl

Copy ID

Reference Book

E6 Medicine Harrison 22e Part 2 pp. 204-206, 206-208