In Reply: In response to Drs Namendys-Silva and Hernández-Garay, the exact adjustment to the PaO2/FIO2 ratio for altitude is unknown. We proposed the adjustment used in the ARDS Network clinical trials.1 Some adjustment is needed because the PaO2 drops with altitude regardless of the FIO2. For example, a normal person breathing 100% oxygen on top of Mt Everest would have an uncorrected PaO2/FIO2 ratio of less than 250 mm Hg and would meet the oxygenation criterion for mild ARDS. In regard to their second point, the Berlin Definition for ARDS did not recommend noninvasive ventilation for mild ARDS; it allowed patients to meet criteria for mild ARDS while being ventilated noninvasively with 5 cm H2O or greater of PEEP or CPAP. The diagnosis of more severe forms of ARDS in patients without endotracheal delivery of oxygen are complicated by the unreliable assessment of FIO2.2
Rubenfeld GD, Slutsky AS, Thompson BT, ARDS Definition Task Force FT. Definition of Acute Respiratory Distress Syndrome—Reply. JAMA. 2012;308(13):1321. doi:10.1001/2012.jama.11901
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