i. PaO2/FiO2 < 150 with PEEP >/= 8 cm H2O OR, if ABG not available, SaO2/FiO2 ratio that is equivalent to a PaO2/FiO2 < 150 with PEEP >/= 8 cm H2O , and a confirmatory SaO2/FiO2 ratio that is again equivalent 1-6 hours later