• PaO2:FiO2 <80 mmHg for >6 hrs
  • PaO2:FiO2 <50 mmHg for >3 hrs
  • pH <7.25 with PaCO2 ≤60 mmHg for >6 hrs*
*With respiratory rate increased to 35 breaths per minute and mechanical ventilation settings adjusted to keep a plateau airway pressure of ≤32 cm H2O.