Respiratory Critical Care: ARDS, Ventilation, and Escalation
Respiratory critical care tests the recognition and ventilatory management of acute respiratory failure, ARDS, sepsis, and weaning. The emphasis is on physiology, ventilator settings, and avoiding harm.
Core rules
- ARDS (Berlin) requires acute onset within 1 week, bilateral opacities not fully explained by effusion, collapse, or nodule, respiratory failure not fully explained by cardiac failure, and P/F ratio ≤300 mmHg on PEEP ≥5 cmH2O.
- Use lung-protective ventilation: tidal volume 6 mL/kg predicted body weight (range 4–8), plateau pressure ≤30 cmH2O, and permissive hypercapnia unless contraindicated.
- Prone positioning improves survival in moderate-to-severe ARDS; use for 12–16 hours per day.
- NIV is first-line in hypercapnic exacerbations of COPD and cardiogenic pulmonary oedema; it is not routine in de novo hypoxaemic failure.
Worked example
A 48-year-old with pneumonia has PaO2/FiO2 120 on PEEP 10, bilateral infiltrates, and no cardiac cause. This is moderate ARDS. Set tidal volume 6 mL/kg predicted body weight, target plateau ≤30, apply PEEP, consider prone positioning, and treat the cause. If oxygenation remains poor, escalate to advanced therapies.
Traps
Using actual rather than predicted body weight; accepting high plateau pressures; overusing NIV in hypoxaemic ARDS; and missing a pneumothorax or pulmonary embolism as a cause of sudden deterioration.