Critical Care · Year 4 · from Critical Care
Case 2: ARDS Requiring Escalating Respiratory Support
Clinical Image
Source: Wikimedia Commons - ARDS X-Ray - Public Domain
Case Presentation
A 55-year-old man with no significant past medical history presents to the emergency department with 5 days of progressive cough, fever, and dyspnea. He initially had mild upper respiratory symptoms but has rapidly deteriorated over the past 48 hours. On examination, vital signs show temperature 38.8C (101.8F), heart rate 110 bpm, respiratory rate 32/min with accessory muscle use, blood pressure 138/78 mmHg, and oxygen saturation 82% on 15L non-rebreather mask. He appears in severe respiratory distress with diffuse crackles bilaterally on auscultation. Chest X-ray shows bilateral diffuse alveolar infiltrates without cardiomegaly. Initial ABG on high-flow oxygen shows pH 7.31, PaCO2 48 mmHg, PaO2 58 mmHg, with P/F ratio of 97. He is emergently intubated and placed on mechanical ventilation. Initial settings include tidal volume 6 mL/kg ideal body weight (420 mL for his 70 kg IBW), respiratory rate 22/min, FiO2 100%, and PEEP 12 cmH2O. Post-intubation ABG shows improved PaO2 of 85 mmHg. He is diagnosed with severe ARDS (P/F ratio less than 100) secondary to viral pneumonia. Following ICU admission, he receives lung-protective ventilation with close monitoring of plateau pressure (maintained below 30 cmH2O), driving pressure optimization, and consideration for prone positioning given his severe hypoxemia.
Key Learning Points
- ARDS is diagnosed using the Berlin criteria: acute onset (within 1 week), bilateral opacities on imaging not explained by effusions/collapse/nodules, respiratory failure not fully explained by cardiac failure, and P/F ratio classification (mild 200-300, moderate 100-200, severe less than 100)
- Lung-protective ventilation (6 mL/kg IBW, plateau pressure less than 30 cmH2O) reduces mortality in ARDS and should be applied to all mechanically ventilated patients
- The P/F ratio (PaO2/FiO2) is the key metric for classifying ARDS severity and guiding treatment escalation
- Severe ARDS (P/F less than 100-150) may benefit from prone positioning, which has been shown to reduce mortality