Table 1.
Characteristics of Trial Participants by APACHE-II
| Variable | Low APACHE-II* (n = 99) |
High APACHE-II* (n = 101) |
Difference (95% CI)† |
|---|---|---|---|
| Age | 57 (42 to 67) | 58 (47 to 67) | −2 (–7 to 3) |
| Sex, F, n (%) | 52 (52.5) | 40 (39.6) | 12.9 (–0.8 to 26.6) |
| Weight, kg | 85.4 (72.0 to 110.3) | 77.8 (69.0 to 96.5) | 7.6 (1.3 to 14.1) |
| Body mass index, kg/m2 | 31.1 (26.4 to 39.7) | 28.3 (24.8 to 33.4) | 2.7 (0.7 to 4.9) |
| Time intubated prior to enrollment, h | 21.5 (15 to 30) | 21 (13 to 33) | 0 (–4 to 4) |
| APACHE-II at enrollment | 21 (4) | 33 (4) | −12 (–14 to –11) |
| Acute physiology subscore | 18 (4) | 30 (4) | −12 (–13 to –11) |
| Chronic health subscore | 3 (2) | 3 (2) | −1 (–1 to 0) |
| SOFA at enrollment | 8.5 (6 to 10) | 13 (12 to 15) | −5 (–6 to –4) |
| ARDS risk factor, n (%) | |||
| Sepsis | 87 (87.9) | 84 (83.2) | 4.7 (–5.0 to 14.4) |
| Pneumonia | 78 (78.8) | 71 (70.3) | 8.5 (–3.5 to 20.5) |
| Aspiration | 17 (17.2) | 25 (24.8) | −7.6 (–18.8 to 3.7) |
| Multiple transfusions | 5 (5.1) | 14 (13.9) | −8.8 (–16.8 to –0.8) |
| Acute pancreatitis | 1 (1.0) | 6 (5.9) | −4.9 (–9.9 to 0.1) |
| Trauma | 3 (3.0) | 3 (3.0) | −0.1 (–5.7 to 4.8) |
| Any pulmonary risk factor | 87 (87.9) | 83 (82.2) | 5.7 (–4.2 to 15.6) |
| Respiratory characteristics at enrollment | |||
| pH | 7.36 (7.31 to 7.40) | 7.29 (7.23 to 7.35) | 0.06 (0.04 to 0.08) |
| PaCO2, mm Hg | 45 (37 to 52) | 43 (37 to 50) | 1 (–2 to 4) |
| PaO2:FiO2 | 95 (75 to 132) | 86 (69 to 119) | 7 (–4 to 16) |
| Vt, ml/kg PBW | 6.2 (5.9 to 6.8) | 6.1 (5.9 to 7.0) | 0.1 (–0.1 to 0.3) |
| Respiratory rate, breaths/min | 25 (22 to 29) | 26 (23 to 30) | −2 (–3 to 0) |
| e, L/min | 9.4 (8.4 to 11.2) | 10.2 (8.5 to 12.2) | −0.5 (–1.3 to 0.2) |
| Ventilatory ratio‡ | 1.9 (1.6 to 2.3) | 2.0 (1.6 to 2.3) | 0.0 (–0.2 to 0.1) |
| Set PEEP, cm H2O | 14 (10 to 16) | 14 (10 to 16) | 0 (–2 to 1) |
| Plateau airway pressure, cm H2O | 28 (24 to 31) | 27 (25 to 31) | 0 (–1 to 2) |
| Driving airway pressure, cm H2O | 13 (10 to 15) | 13 (10 to 14) | 0 (–1 to 1) |
| Pes, cm H2O | |||
| At end-expiration | 16 (12 to 19) | 16 (13 to 18) | −1 (–2 to 1) |
| At end-inspiration | 18 (15 to 21) | 19 (16 to 21) | −1 (–2 to 0) |
| Transpulmonary pressure, cm H2O | |||
| At end-expiration | −1 (–4 to 2) | −1 (–3 to 1) | 0 (–1 to 1) |
| At end-inspiration | 8 (5 to 12) | 8 (5 to 11) | 0 (–1 to 2) |
| Cointerventions at enrollment, n (%) | |||
| Vasopressors | 45 (45.5) | 69 (68.3) | −22.9 (–36.2 to –9.5) |
| Neuromuscular blockade | 28 (28.3) | 38 (37.6) | −9.3 (–22.3 to 3.6) |
| Systemic corticosteroids | 34 (34.3) | 35 (34.7) | −0.3 (–13.5 to 12.9) |
| Treatment assignment, n (%) | |||
| Pes-guided PEEP | 51 (51.5) | 51 (50.5) | 1.0 (–12.8 to 14.9) |
| Empirical PEEP | 48 (48.5) | 50 (49.5) | −1.0 (–14.9 to 12.8) |
| Outcomes | |||
| 28-d mortality, n (%) | 21 (21.2) | 42 (41.6) | −20.4 (–32.9 to –7.8) |
| 60-d mortality, n (%) | 29/98 (29.6) | 46/101 (45.5) | −15.9 (–29.2 to –2.7) |
| Ventilator-free days through Day 28 | 20 (0 to 24) | 9 (0 to 22) | 2 (0 to 6) |
| Shock-free days through Day 28 | 18 (7 to 22) | 9 (0 to 20) | 4 (1 to 7) |
Definition of abbreviations: APACHE-II = Acute Physiology and Chronic Health Evaluation II; ARDS = acute respiratory distress syndrome; CI = confidence interval; PBW = predicted body weight; PEEP = positive end-expiratory pressure; Pes = esophageal pressure; SOFA = sequential organ failure assessment.
Data are shown as median (interquartile range) unless otherwise indicated.
Low and high APACHE-II refer to patients with values less or greater than the median APACHE-II score, which was 27.5.
Hodges-Lehmann estimation was used to determine unbiased median differences and 95% CIs for variables reported as median (interquartile range). The result represents the median difference among all possible pairs formed by one patient from each group and thus does not necessarily equal the crude difference between group medians.
Ventilatory ratio is a surrogate for dead-space fraction calculated as [e (ml/min) × PaCO2 (mm Hg)]/(predicted body weight × 100 × 37.5).