Table 2.
Variables Associated with the Propensity to Use Lower Positive End-Expiratory Pressure Relative to the ARDS Network Model
| Variable | Overall (N = 1,047) | High PEEP/On-Protocol PEEP (n = 745) | Low PEEP (n = 302) | P Value |
|---|---|---|---|---|
| Demographics | ||||
| Age, mo | 46.8 (13.2–141.0) | 49.2 (13.2–132.4) | 42.0 (11.9–154.0) | 0.99 |
| Sex, male | 574 (54.8) | 404 (54.2) | 170 (56.3) | 0.54 |
| Race (n = 979) | 0.002 | |||
| White | 284 (29.0) | 223 (31.7) | 61 (22.2) | |
| Hispanic | 299 (30.5) | 193 (27.4) | 106 (38.6) | |
| Black | 182 (18.6) | 135 (19.2) | 47 (17.1) | |
| Other race | 214 (21.9) | 153 (21.7) | 61 (22.2) | |
| ARDS trigger (n = 979) | ||||
| Pneumonia | 611 (58.4) | 443 (59.5) | 168 (55.6) | 0.25 |
| Sepsis | 303 (28.9) | 202 (27.1) | 101(33.4) | 0.04 |
| Drowning | 19 (1.9) | 14 (2.0) | 5 (1.8) | 0.86 |
| Aspiration | 70 (7.1) | 55 (7.8) | 15 (5.4) | 0.20 |
| Trauma | 62 (6.4) | 43 (6.1) | 20 (7.3) | 0.5 |
| Dataset | <0.001 | |||
| CHLA 2000–2007 | 306 (29.3) | 162 (52.9) | 144 (47.1) | |
| CHLA 2009–2013 | 246 (23.5) | 168 (68.3) | 78 (31.7) | |
| CHOP | 427 (40.8) | 374 (87.6) | 53 (12.4) | |
| CPCCRN | 68 (6.5) | 41 (60.3) | 27 (39.7) | |
| Comorbidities (n = 979) | ||||
| Immunodeficiency | 230 (23.5) | 170 (24.1) | 60 (21.9) | 0.44 |
| Cancer | 150 (15.3) | 115 (16.3) | 35 (12.7) | 0.15 |
| Stem cell transplant | 57 (5.8) | 45 (6.4) | 12 (4.3) | 0.22 |
| Solid organ transplant | 40 (4.1) | 31 (4.4) | 9 (3.3) | 0.42 |
| Neurologic disease | 237 (24.2) | 164 (23.3) | 73 (26.6) | 0.29 |
| Data at PARDS diagnosis | ||||
| PARDS severity | <0.001 | |||
| PF > 300 | 32 (2) | 24 (3.2) | 8 (2.7) | |
| PF 200–300 | 252 (24.1) | 211 (28.3) | 41 (13.6) | |
| PF 100–200 | 472 (45.1) | 357 (47.9) | 115 (38.15) | |
| P ≤ 100 | 291 (27.8) | 153 (20.5) | 138 (45.7) | |
| PRISM III raw score | 11 (6–17) | 11 (5–17) | 11 (6–19) | 0.05 |
| PF ratio | 147 (91–207) | 156 (109–217) | 109 (66–162) | <0.001 |
| OI | 10 (6.3–17.7) | 9.1 (6.0–14.3) | 12.2 (6.7–24.2) | <0.001 |
| FiO2 | 0.60 (0.44–0.90) | 0.50 (0.40–0.75) | 0.79 (0.50–1.00) | <0.001 |
| PEEP, cm H2O | 8.0 (6.0–10.0) | 8.0 (6.6–10.0) | 6.0 (5.0–10.0) | <0.001 |
| Data over first 24 h (n = 974) | ||||
| PARDS severity | <0.001 | |||
| PF > 300 | 113 (11) | 92 (12.5) | 21 (7.2) | |
| PF 200–300 | 400 (39) | 341 (46.5) | 59 (20.2) | |
| PF 100–200 | 405 (39.5) | 264 (40) | 141 (48.3) | |
| PF ≤ 100 | 108 (10.5) | 37 (5.1) | 71 (24.3) | |
| PF category improved | 387 (37.7) | 281 (38.2) | 106 (36.6) | 0.8 |
| PaO2, mm Hg (n = 862) | 89 (76–108) | 89 (78–106) | 89 (73–111) | 0.49 |
| Day 1 average PaO2 range | n = 862 | n = 624 | n = 238 | <0.001 |
| PaO2 ≤ 60 mm Hg | 40 (4.6) | 19 (3) | 21 (8.8) | |
| PaO2 60–80 mm Hg | 240 (27.8) | 167 (26.8) | 73 (30.7) | |
| PaO2 80–100 mm Hg | 300 (34.8) | 246 (39.4) | 54 (22.7) | |
| PaO2 > 100 mm Hg | 282 (32.7) | 192 (30.8) | 90 (37.8) | |
| OI | 7.6 (5.3–13.0) | 7.0 (5.2– 10.5) | 10.0 (5.4–19.3) | <0.001 |
| FiO2 | 0.47 (0.40–0.60) | 0.44 (0.38–0.52) | 0.61 (0.50–0.80) | <0.001 |
| PEEP, cm H2O | 8.8 (6.7–10.8) | 9.4 (8.0–10.9) | 7.0 (5.0–10.0) | <0.001 |
| Vt, ml/kg | 7.5 (6.5–8.6) | 7.7 (6.5–9.0) | 7.5 (6.5–8.6) | 0.50 |
| PIP, cm H2O | 28 (24.5–33) | 28 (24.6–32) | 29.5 (24–34) | 0.32 |
| Driving pressure, cm H2O | 19.5 (16–23) | 19 (15.6–22) | 20.1 (17.2–25.5) | <0.001 |
| Inotropes | 598 (61.0) | 446 (63.0) | 152 (55.2) | 0.02 |
| Nitric oxide | 195 (19.9) | 132 (18.8) | 63 (22.9) | 0.14 |
| Outcome | ||||
| Mortality | 191 (18.2) | 111 (14.9) | 80 (26.5) | <0.001 |
| 28-day ventilator-free days | 17.0 (0–22) | 17.4 (3.0–22.1) | 15.6 (0–21.2) | 0.02 |
For definition of abbreviations, see Table 1.
Data are presented as median (interquartile range) or n (%). When a PaO2 metric was not available, PF was calculated from ratio of oxygen saturation measured by pulse oximetry to FiO2, and OI was calculated from OSI using previously published formulae (19). A total of 1,047 patients had PEEP/FiO2 data available for analysis. Race, ARDS triggers, and comorbidities were not available in the CPCCRN data, so the total number is reduced to 979. Some patients did not have available data 24 hours after PARDS diagnosis (died, extubated, or no PF ratio, OI, or OSI available), so the number is reduced to 974. Twenty-eight–day ventilator-free days defined as the number of days in the first 28 days after ARDS diagnosis in which the patient was alive and not on invasive mechanical ventilation. The percentages refer to the percent overall patients, high/on-protocol PEEP, or low PEEP with a given variable. P values are comparing the difference between two PEEP groups, among variables or groupings of variables (i.e., P < 0.001 for PARDS severity implies difference in PARDS severity categories between high/on-protocol PEEP and low PEEP without post hoc comparison of which groups are different).