Table 3.
Clinical outcomes according to groups before and after matching
| Unmatched cohort, n=933 | Matched cohort, n=468 | |||||||
| High PEEP, n=259 | Low PEEP, n=674 | Effect estimate (95% CI) | P | High PEEP, n=234 | Low PEEP, n=234 | Effect estimate (95% CI) | P | |
| Primary outcome | ||||||||
| Ventilator-free days at day 28 (days) | 2.0 [0.0 to 15.0] | 0.0 [0.0 to 16.0] | 0.21 (−3.34 to 3.78)a | 0.905 | 0.0 [0.0 to 14.0] | 6.0 [0.0 to 17.0] | −4.65 (−8.92 to −0.39)a | 0.032 |
| Mean ± SD | 7.5 ± 8.7 | 7.6 ± 8.8 | 6.9 ± 8.5 | 8.5 ± 8.8 | ||||
| Secondary outcomes | ||||||||
| Duration of ventilation (days) | 14.5 [7.0 to 24.0] | 13.0 [8.0 to 22.3] | 1.03 (0.75 to 1.42)b | 0.850 | 15.0 [7.0 to 25.0] | 13.0 [9.0 to 22.0] | 0.79 (0.58 to 1.09)b | 0.150 |
| In survivors at day 28 (days) | 17.0 [9.0 to 27.8] | 15.0 [9.0 to 28.0] | 18.0 [10.0 to 29.0] | 14.0 [9.0 to 24.5] | ||||
| Tracheostomy | 42/257 (16.3) | 105 (15.6) | 0.95 (0.61 to 1.48)c | 0.830 | 39/233 (16.7) | 34 (14.5) | 0.80 (0.44 to 1.48)c | 0.486 |
| Reintubation | 29/256 (11.3) | 88/671 (13.1) | 0.90 (0.56 to 1.45)c | 0.673 | 26/232 (11.2) | 30/232 (12.9) | 0.87 (0.48 to 1.57)c | 0.646 |
| Pneumothorax | 4/252 (1.6) | 3/643 (0.5) | 3.97 (0.76 to 20.70)c | 0.102 | 4/228 (1.8) | 1/225 (0.4) | 4.02 (0.35 to 46.51)c | 0.265 |
| Thromboembolic complications | 72 (27.8) | 202 (30.0) | 0.80 (0.57 to 1.15)c | 0.227 | 68 (29.1) | 72 (30.8) | 0.87 (0.56 to 1.36)c | 0.544 |
| Pulmonary embolism | 55 (21.2) | 155 (23.0) | 0.81 (0.54 to 1.19)c | 0.281 | 53 (22.6) | 56 (23.9) | 0.89 (0.54 to 1.46)c | 0.643 |
| Deep vein thrombosis | 9 (3.5) | 41 (6.1) | 0.77 (0.32 to 1.84)c | 0.559 | 9 (3.8) | 19 (8.1) | 0.54 (0.21 to 1.39)c | 0.201 |
| Ischaemic stroke | 9 (3.5) | 21 (3.1) | 1.33 (0.56 to 3.17)c | 0.519 | 8 (3.4) | 3 (1.3) | 2.99 (0.73 to 12.26)c | 0.128 |
| Myocardial infarction | 3 (1.2) | 13 (1.9) | 0.61 (0.17 to 2.26)c | 0.460 | 2 (0.9) | 4 (1.7) | 0.50 (0.09 to 2.73)c | 0.420 |
| Systemic arterial embolism | 0 (0.0) | 4 (0.6) | – | – | 0 (0.0) | 1 (0.4) | – | – |
| Acute kidney injury | 134/257 (52.1) | 303/672 (45.1) | 1.36 (0.99 to 1.86)c | 0.056 | 129/232 (55.6) | 107/233 (45.9) | 1.49 (1.02 to 2.18)c | 0.039 |
| Need for RRT | 62 (23.9) | 113 (16.8) | 1.54 (1.05 to 2.27)c | 0.027 | 60 (25.6) | 42 (17.9) | 1.58 (1.01 to 2.46)c | 0.045 |
| Need of rescue therapyd | 188/258 (72.9) | 526/670 (78.5) | 0.86 (0.59 to 1.26)c | 0.444 | 175/233 (75.1) | 183/232 (78.9) | 0.83 (0.51 to 1.35)c | 0.450 |
| Prone positioning | 129/257 (50.2) | 426/670 (63.6) | 0.66 (0.46 to 0.94)c | 0.023 | 121/232 (52.2) | 141/233 (60.5) | 0.71 (0.44 to 1.12)c | 0.142 |
| Recruitment manoeuvre | 16/196 (8.2) | 40/575 (7.0) | 1.22 (0.60 to 2.5)c | 0.588 | 15/175 (8.6) | 13/202 (6.4) | 1.45 (0.59 to 3.61)c | 0.420 |
| Use of NMBA | 125 (48.3) | 337 (50.0) | 0.98 (0.70 to 1.39)c | 0.931 | 116 (49.6) | 124 (53.0) | 0.95 (0.61 to 1.48)c | 0.825 |
| ECMO | 1/258 (0.4) | 7 (1.1) | 0.37 (0.04 to 2.99)c | 0.348 | 1/233 (0.4) | 3/229 (1.3) | 0.32 (0.03 to 3.14)c | 0.332 |
| Use of continuous sedationd | 259 (100.0) | 669 (99.3) | – | – | 234 (100.0) | 233 (99.6) | – | – |
| Use of inotrope or vasopressord | 250 (96.5) | 640 (95.0) | 1.40 (0.64 to 3.07)c | 0.402 | 227 (97.0) | 222 (94.9) | 1.78 (0.67 to 4.74)c | 0.250 |
| Use of vasopressor | 250 (96.5) | 639 (94.8) | 1.46 (0.67 to 3.17)c | 0.342 | 227 (97.0) | 221 (94.4) | 1.91 (0.75 to 4.87)c | 0.177 |
| Use of inotrope | 12 (4.6) | 84 (12.5) | 0.59 (0.28 to 1.27)c | 0.177 | 11 (4.7) | 33 (14.1) | 0.65 (0.26 to 1.65)c | 0.369 |
| ICU length of stay (days) | 16.0 [9.0 to 27.0] | 15.0 [9.0 to 26.0] | 1.15 (0.95 to 1.40)e | 0.140 | 16.0 [9.0 to 28.0] | 15.0 [10.0 to 25.0] | 0.86 (0.68 to 1.09)e | 0.230 |
| In survivors (days) | 19.5 [11.8 to 30.3] | 18.0 [11.0 to 30.8] | 20.0 [12.0 to 31.8] | 16.0 [11.0 to 29.0] | ||||
| Hospital length of stay (days) | 24.0 [13.0 to 39.0] | 23.0 [15.0 to 37.0] | 1.14 (0.93 to 1.40)e | 0.190 | 23.5 [13.0 to 40.0] | 24.5 [17.0 to 36.0] | 0.88 (0.69 to 1.13)e | 0.310 |
| In survivors (days) | 31.0 [20.0 to 47.0] | 30.0 [21.0 to 45.0] | 32.0 [20.0 to 48.0] | 28.0 [21.0 to 41.3] | ||||
| ICU mortality | 77/254 (30.3) | 239/664 (36.0) | 0.75 (0.53 to 1.05)c | 0.097 | 77/231 (33.3) | 69/232 (29.7) | 1.24 (0.80 to 1.91)c | 0.332 |
| Hospital mortality | 79/242 (32.6) | 246/647 (38.0) | 0.76 (0.54 to 1.08)c | 0.124 | 79/223 (35.4) | 74/226 (32.7) | 1.18 (0.77 to 1.82)c | 0.451 |
| 28-Day mortality | 71/255 (27.8) | 216/668 (32.3) | 0.85 (0.63 to 1.14)e | 0.270 | 71/230 (30.9) | 63/233 (27.0) | 1.30 (0.90 to 1.88)e | 0.170 |
| 90-Day mortality | 79/242 (32.6) | 259/625 (41.4) | 0.77 (0.58 to 1.02)e | 0.067 | 79/220 (35.9) | 78/214 (36.4) | 1.15 (0.81 to 1.64)e | 0.430 |
Data are median [IQR], mean ± SD or number (%). Percentages may not total 100 because of rounding. CI, confidence interval; ECMO, extracorporeal membrane oxygenation; NMBA, neuromuscular blocking agent; PEEP, positive end-expiratory pressure; RRT, renal replacement therapy.
Median difference from a mixed-effect quantile model considering a Τ = 0.50 and an asymmetric Laplace distribution. P values were extracted after 1000 bootstrap samplings.
Subdistribution hazard ratio from a clustered Fine–Gray competing risk model, with death before extubation treated as competing risk.
Odds ratio from mixed-effect logistic regression models.
Assessed in the first 4 days of ventilation.
Hazard ratio from a (shared-frailty) Cox proportional hazard model. For the ICU and hospital length of stay analyses, all patients who died prior to discharge were assigned the maximum length of stay to account for death as a competing risk in this model. P value for Schoenfeld residuals: ICU length of stay (P = 0.420 in the unmatched cohort and P = 0.330 for the matched cohort); hospital length of stay (P = 0.830 in the unmatched cohort and P = 0.770 for the matched cohort); 7-day mortality (P = 0.380 in the unmatched cohort and P = 0.780 in the matched cohort); 28-day mortality (P = 0.260 in the unmatched cohort and P = 0.110 in the matched cohort); 90-day mortality (P = 0.100 in the unmatched cohort and P = 0.055 in the matched cohort).