Table 1.
Characteristics of included studies
| Study characteristic | Number of studies* | ||
|---|---|---|---|
| Overall | ICU | OR | |
| Number of studies, N | 271 | 216 | 55 |
| Study design, n/total N (%) | |||
| Observational | 163/271 (60%) | 147/216 (68%) | 16/55 (29%) |
| RCT | 73/271 (27%) | 39/216 (18%) | 34/55 (62%) |
| Nonrandomized trial | 14/271 (5%) | 13/216 (6%) | 1/55 (2%) |
| Randomized crossover | 13/271 (5%) | 12/216 (6%) | 1/55 (2%) |
| Reanalysis | 8/271 (3%) | 5/216 (2%) | 3/55 (6%) |
| Continent of origin,† n/total N (%) | |||
| Europe | 139/271 (51%) | 114/216 (53%) | 25/55 (46%) |
| Asia | 67/271 (25%) | 46/216 (21%) | 21/55 (38%) |
| North America | 38/271 (14%) | 36/216 (17%) | 2/55 (4%) |
| South America | 19/271 (7%) | 15/216 (7%) | 4/55 (7%) |
| Africa | 10/271 (4%) | 8/216 (4%) | 2/55 (4%) |
| Australia/New Zealand | 9/271 (3%) | 8/216 (4%) | 1/55 (2%) |
| Time period, n/total N (%) | |||
| 1970s | 4/271 (2%) | 4/216 (2%) | 0/55 (0%) |
| 1980s | 12/271 (4%) | 12/216 (6%) | 0/55 (0%) |
| 1990s | 10/271 (4%) | 10/216 (5%) | 0/55 (0%) |
| 2000s | 34/271 (13%) | 32/216 (15%) | 2/55 (4%) |
| 2010s | 100/271 (37%) | 85/216 (39%) | 15/55 (27%) |
| 2020s | 111/271 (41%) | 73/216 (34%) | 38/55 (69%) |
| Patient population,† n/total N (%) | |||
| ARDS | 162/271 (60%) | 162/216 (75%) | 0/55 (0%) |
| Normal | 46/271 (17%) | 0/216 (0%) | 46/55 (84%) |
| Laparoscopic | 30/271 (11%) | 0/216 (0%) | 30/55 (55%) |
| COVID-19 | 27/271 (10%) | 27/216 (13%) | 0/55 (0%) |
| Obese | 25/271 (9%) | 16/216 (7%) | 9/55 (16%) |
| Mixed | 22/271 (8%) | 22/216 (10%) | 0/55 (0%) |
| AHRF | 12/271 (4%) | 12/216 (6%) | 0/55 (0%) |
| COPD | 10/271 (4%) | 10/216 (5%) | 0/55 (0%) |
| Postoperative | 10/271 (4%) | 10/216 (5%) | 0/55 (0%) |
| ECMO | 10/271 (4%) | 10/216 (5%) | 0/55 (0%) |
| Proned | 6/271 (2%) | 4/216 (2%) | 2/55 (4%) |
Included studies are stratified by overall and study setting
*Percentages are for total studies within given column
†Sum of columns is greater than total as some articles fit more than one category
AHRF = acute hypoxemic respiratory failure; ARDS = acute respiratory distress syndrome; COPD = chronic obstructive pulmonary disease; ECMO = extracorporeal membrane oxygenation; ICU = intensive care unit; OR = operating room; RCT = randomized controlled trial