Physiologic Markers of Disease Severity in ARDS.

Despite its significant limitations, the ratio between the partial pressure of arterial oxygen and the fraction of inspired oxygen, the PaO2/FiO2 ratio, remains the standard tool to classify disease severity in ARDS. Treatment decisions and research enrollment have depended on this parameter for over fifty years. In addition, several variables have been studied over the past few decades, incorporating other physiologic considerations such as ventilation efficiency, lung mechanics, and right ventricular performance. This review describes the strengths and limitations of all relevant parameters, with the goal of helping us better understand disease severity and possible future treatment targets.