Table 1.
Interaction of CRS with the severity of ARDS, the presence of hypercarbia, and the value of PEEP
| Number of studies | Number of patients | Pooled estimate of CRS, mL/cm H2O (95% CI) | Heterogeneity and between-studies variance | |
|---|---|---|---|---|
| PaO2/FiO2 ratio (pinteraction<0·0001) | ||||
| >200 to 300 mm Hg | 3 | 154 | 39·3 (36·6–42·0) | I2=43·4%, τ2=2·4 |
| >100 to 200 mm Hg | 38 | 11 142 | 34·9 (32·8–36·9) | I2=97·0%, τ2=37·9 |
| ≤100 mm Hg | 6 | 471 | 27·3 (23·3–31·2) | I2=84·3%, τ2=17·7 |
| PaCO2 (pinteraction=0·052) | ||||
| >45 mm Hg | 16 | 2814 | 31·5 (27·7–35·4) | I2=98·2%, τ2=56·6 |
| ≤45 mm Hg | 13 | 7738 | 36·5 (33·3–39·6) | I2=97·8%, τ2=31·7 |
| PEEP (pinteraction=0·80) | ||||
| >15 cm H2O | 7 | 410 | 35·2 (27·6–42·8) | I2=92·3%, τ2=95·5 |
| ≤15 cm H2O | 41 | 11 685 | 34·2 (32·3–36·2) | I2=97·6%, τ2=37·9 |
Severity of ARDS was assessed using the PaO2/FiO2 ratio (mild, >200 to 300 mm Hg; moderate, >100 to 200 mm Hg; or severe, ≤100 mm Hg). The presence of hypercarbia was assessed using PaCO2 (>45 mm Hg vs ≤45 mm Hg). PEEP values were high or low (>15 cm H2O vs ≤15 cm H2O) compared with patients with mild ARDS (PaO2/FiO2 ratio >200 to 300 mm Hg). ARDS=acute respiratory distress syndrome. CRS=respiratory system static compliance. FiO2=fractional inspired oxygen. PaCO2=partial pressure of carbon dioxide in arterial blood. PaO2=partial pressure of oxygen in arterial blood. PEEP=positive end-expiratory pressure.