Table 1.
General characteristics and respiratory mechanics of patients
| General characteristics | Overall | Survivors | Non-survivors | P value* |
|---|---|---|---|---|
| (n = 377) | (n = 235) | (n = 142) | ||
| Males—no. (%) | 266 (70.6) | 169 (71.9) | 97 (68.3) | 0.530 |
| Age—years | 60 [46, 69] | 56 [43, 66] | 65 [53, 76] | < 0.001 |
| Height—cm | 171 [164, 178] | 171 [164, 178] | 170 [163, 178] | 0.980 |
| Body Mass Index—kg/m2 | 28 [24, 34] | 28 [24, 33] | 28 [24, 35] | 0.674 |
| APACHE II at ICU admission | 24 [16, 30] | 23 [16, 28] | 27 [17, 32] | 0.016 |
| ICU stay prior to enrollment—days | 2 [1, 5] | 2 [1, 6] | 2 [1, 4] | 0.963 |
| IMV days prior to enrollment—days | 2 [1, 4] | 2 [1, 5] | 2 [1, 4] | 0.350 |
| SOFA at enrollment | 11 [8, 14] | 10 [7, 13] | 12 [9, 16] | < 0.001 |
| Clinical PEEP at enrollment—cmH2O | 12 [10, 14] | 12 [10, 14] | 12 [10, 14] | 0.615 |
| PaO2/FiO2 at enrollment—mmHg | 128 [100, 162] | 138 [103, 168] | 115 [88, 150] | 0.001 |
| VE,corr—L/min | 12.3 [10.4, 14.5] | 12.3 [10.3, 14.2] | 12.3 [10.5, 14.8] | 0.630 |
| Severity of ARDS—no. (%) | 0.024 | |||
| Mild | 38 (11.1) | 28 (13.2) | 10 (7.6) | |
| Moderate | 232 (67.6) | 148 (69.8) | 84 (64.1) | |
| Severe | 73 (21.3) | 36 (17) | 37 (28.2) | |
| Pulmonary ARDS—no. (%) | 262 (69.5) | 169 (72) | 93 (65.2) | 0.197 |
| 60-day mortality—no. (%) | 142 (37.7) | |||
| Global mechanics | (n = 377) | (n = 235) | (n = 142) | |
| PEEP—cmH2O | 12 [10, 15] | 12 [10, 15] | 12 [10, 15] | 0.153 |
| VT/PBW—ml/kg | 6.2 [5.9, 6.5] | 6.1 [5.9, 6.5] | 6.3 [5.9, 6.5] | 0.542 |
| Auto-PEEP—cmH2O | 1 [0, 1] | 1 [0, 1] | 1 [0, 1] | 0.522 |
| Pplat—cmH2O | 25 [23, 28] | 25 [22, 28] | 26 [24, 30] | < 0.001 |
| DPaw—cmH2O | 12 [10, 14] | 11 [9, 13] | 13 [10, 15] | 0.001 |
| RR—cmH2O | 28 [24, 30] | 27 [24, 30] | 28 [25, 30] | 0.061 |
| Crs—ml/cmH2O | 35 [27, 43] | 36 [29, 44] | 32 [25, 41] | 0.003 |
| Rrs—cmH2O/L/s | 12 [9, 14] | 12 [9, 14] | 12 [9, 14] | 0.337 |
| Oxygenation stretch index†—mmHg/cmH2O | 11.7 [8.1, 16.2] | 12.3 [9.1, 16.9] | 10.8 [6.8, 14.9] | 0.005 |
| Partitioned mechanics | (n = 302) | (n = 195) | (n = 107) | |
| DPL—cmH2O | 8.3 [6.3, 11] | 8 [6.1, 10.6] | 9.3 [6.9, 12.1] | 0.010 |
| DPcw—cmH2O | 3 [2.7 4.1] | 2.7 [2.7, 4.1] | 3 [2.7, 4.1] | 0.111 |
| CL– ml/cmH2O | 48 [35, 62] | 50 [38, 62] | 44 [30, 61] | 0.009 |
| Ccw—ml/cmH2O | 127 [92, 163] | 130 [98, 165] | 120 [85, 155] | 0.180 |
| EL/Ers ratio | 0.73 [0.63, 0.8] | 0.73 [0.64, 0.79] | 0.73 [0.63, 0.81] | 0.638 |
| Elastance-derived plateau PL—cmH2O | 18.1 [14.5, 21.6] | 17.5 [14.2, 20.8] | 19.1 [15.4, 22.9] | 0.012 |
| Directly-measured end-expiratory PL—cmH2O | − 2.3 ± 5 | − 1.9 ± 4.7 | − 3 ± 5.5 | 0.077 |
| Response to higher PEEP†† | (n = 311) | (n = 194) | (n = 117) | |
| Higher PEEP—cmH2O | 15 [14, 17] | 15 [14, 17] | 15 [14, 17] | 0.660 |
| Lower PEEP—cmH2O | 10 [9, 12] | 10 [9, 12] | 10 [9, 12] | 0.307 |
| ΔPaO2/FiO2—mmHg | 14 [− 3, 36] | 16 [− 4, 36] | 14 [− 2, 34] | 0.696 |
| ΔMAP—mmHg | − 2 [− 5, 2] | − 1 [− 5, 2] | − 2 [− 5, 1] | 0.735 |
| ΔDPaw—cmH2O | 1 [0, 2] | 1 [0, 2] | 1 [0, 2] | 0.503 |
| ΔDPL—cmH2O | 1 [0, 2] | 1 [0, 2] | 1.4 [0, 3] | 0.110 |
| ΔEnd-expiratory PL—cmH2O | 3.6 [2.6, 5] | 3.6 [2.6, 5] | 3.6 [2.3, 4.4] | 0.276 |
Categorical variables are described in numbers (percentage); continuous variables are described as mean ± standard derivation or median [interquartile ranges], as appropriate
*Comparing survivors with non-survivors using t-test or Mann–Whitney U-test or chi-square, as appropriate. P values were not corrected for multiple comparisons
†Oxygenation stretch index was measured in total 318 patients, of which 194 survivors and 124 non-survivors
††Measured variables at higher PEEP minus those at lower PEEP. For example, PaO2/FiO2 at high PEEP minus PaO2/FiO2 at lower PEEP
APACHE II Acute Physiology and Chronic Health Evaluation II score, IMV invasive mechanical ventilation, SOFA Sequential Organ Failure Assessment score, PEEP positive end-expiratory pressure, PaO2/FiO2 the ratio of partial pressure of arterial oxygen and fraction of inspired oxygen, VE,corr expired volume per minute corrected by arterial carbon dioxide, PEEP positive end-expiratory pressure, VT/PBW tidal volume per predicted body weight, Pplat airway plateau pressure, DPaw airway driving pressure which is the difference between Pplat and total PEEP, RR respiratory rate, Crs respiratory system compliance, Rrs respiratory system resistance, oxygenation-stretch index PaO2/FiO2 divided by DPaw, DPL transpulmonary driving pressure which is the tidal change in transpulmonary pressure, DPcw chest wall driving pressure which is the tidal change in esophageal pressure, CL lung compliance, Ccw chest wall compliance, EL/Ers ratio lung elastance to respiratory system elastance ratio, PL transpulmonary pressure, PaO2/FiO2 the ratio of partial pressure of arterial oxygen and fraction of inspired oxygen, MAP mean arterial pressure