Table 1.

Patient characteristics, ventilator settings, arterial blood gas results, and outcomes

	All patients (N = 3442)
Demographics
Age, median (IQR), years	51 (39 – 63)
Gender, male (%)	1888 (54.9)
Cause of ARDS, N (%)
Pneumonia	1699 (49.4)
Sepsis	748 (21.7)
Aspiration	429 (12.5)
Trauma	239 (6.9)
Transfusion	71 (2.1)
Others	256 (7.4)

Severity	Severe (≤ 100)			Moderate (101–200)			Mild (201–300)
Categorization	P/F	P/FP	P Value	P/F	P/FP	P Value	P/F	P/FP	P Value
N (%)	640 (19)	794 (30)	< 0.001	1928 (57)	1252 (47)	< 0.001	839 (25)	640 (24)	0.368
Ventilator settings, mean ± SD
FiO2	0.82 ± 0.14	0.79 ± 0.16	< 0.001	0.55 ± 0.14	0.56 ± 0.14	0.049	0.43 ± 0.12	0.49 ± 0.13	< 0.001
PEEP, cmH2O	12.6 ± 4.4	14.2 ± 3.6	< 0.001	9.32 ± 3.5	10.2 ± 2.6	< 0.001	8.0 ± 3.6	8.1 ± 2.4	0.544
PaO2, mmHg
Arterial blood gases	65.0 ± 11.4	71.7 ± 19.7	< 0.001	80.0 ± 19.8	81.9 ± 24.9	0.017	104.5 ± 31.2	96.1 ± 38.2	< 0.001
SaO2, %	91.2 ± 5.7	92.2 ± 5.4	< 0.001	94.6 ± 3.2	94.5 ± 3.7	0.419	96.9 ± 2.3	95.8 ± 3.0	< 0.001
PaCO2, mmHg	43.7 ± 12.9	44.4 ± 13.0	0.309	40.1 ± 9.9	40.3 ± 9.3	0.569	37.8 ± 8.5	38.5 ± 9.0	0.126
pH	7.33 ± 0.10	7.33 ± 0.10	1.000	7.38 ± 0.08	7.38 ± 0.07	1.000	7.39 ± 0.07	7.38 ± 0.07	0.006

P values refer to comparisons between patients classified according to the P/F ratio versus patients classified according to the P/FP ratio in each severity category. Definition of abbreviations: ARDS  acute respiratory distress syndrome, FiO₂  fraction of inspired oxygen, IQR  interquartile range PaCO₂  partial pressure of arterial carbon dioxide, PaO₂  partial pressure of arterial oxygen, PEEP positive end-expiratory pressure, P/F =ratio of the PaO₂ to FiO₂; P/FP = (PaO₂ * 10)/(FiO₂ * PEEP); SaO₂  arterial oxygen saturation; SD standard deviation