TABLE 1.
Selected Baseline Characteristics Before and After Applying Inverse Probability Weighting
| Pre-IP Weighting |
Post-IP Weighting |
|||
|---|---|---|---|---|
| Covariates | Proned Early (n = 702) | Not Proned Early (n = 1,636) | Proned Early | Not Proned Early |
| Demographic characteristics | ||||
| Age, median (IQR) | 60 (51–69) | 63 (53–72) | 61.0 (52.0–70.0) | 62.0 (53.0–71.0) |
| Male sex, n (%) | 474 (67.5) | 1,053 (64.4) | 65.6 | 65.6 |
| White race, n (%) | 271 (38.6) | 620 (37.9) | 36.5 | 37.7 |
| Body mass index (kg/m2), median (IQR) | 31.5 (27.4–37.2) | 30.6 (26.7–35.9) | 31.1 (27.3–36.5) | 30.8 (26.9–36.2) |
| Coexisting conditions, n (%) | ||||
| Coronary artery disease | 73 (10.4) |
227 (13.9) |
12.2 |
12.7 |
| Congestive heart failure | 42 (6.0) | 163 (10.0) | 7.8 | 8.7 |
| Any lung disease | 135 (19.2) | |||
| Symptom onset to ICU admission ≤ 7 d, n (%) | 330 (47.0) | 924 (56.5) | 46.6 | 46.4 |
| Severity of illness on ICU admission, n (%) | ||||
| Pao2/Fio2, mm Hga, n (%) | ||||
| Ventilated and Pao2/Fio2 151–200 | 94 (13.4) | 330 (20.2) | 16.6 | 18.0 |
| Ventilated and Pao2/Fio2 100–150 | 208 (29.6) | 584 (35.7) | 33.4 | 33.7 |
| Ventilated and Pao2/Fio2 ≤ 100 | 400 (57.0) | 722 (44.1) | 50.1 | 48.3 |
| Shock (%), n (%) | 114 (16.2) | 208 (12.7) | 14.5 | 14.0 |
| WBC count (per mm3), n (%) | ||||
| < 4,000 | 31 (4.4) | 77 (4.7) |
5.2 |
4.8 |
| 4,000–11,900 | 448 (63.8) | 1,087 (66.4) | 65.4 | 65.7 |
| ≥ 12,000 | 193 (27.5) | 416 (25.4) | 25.5 | 25.9 |
| Inflammation presentb, n (%) | 551 (78.5) | 1,186 (72.5) | 74.3 | 74.3 |
| Therapies administered, n (%) | ||||
| Corticosteroids | 149 (21.2) | 217 (13.3) | 15.6 | 15.5 |
| Therapeutic anticoagulation | 107 (15.2) | 265 (16.2) | 15.6 | 15.8 |
| Neuromuscular blockade | 176 (25.0) | 218 (13.3) | 17.4 | 17.0 |
| Tocilizumab | 54 (7.7) | 94 (5.7) | 6.6 | 6.4 |
| Hospital characteristics | ||||
| ICU bed size, n (%) | ||||
| < 60 | 372 (53.0) | 605 (37.0) | 43.1 | 42.1 |
| 60–119 | 199 (28.3) | 686(41.9) | 36.4 | 37.7 |
| ≥ 120 | 131 (18.7) | 345 (21.1) | 20.5 | 20.2 |
| Regional density of coronavirus disease 2019, quartilec, n (%) | ||||
| 1 | 41 (5.8) | 147 (9.0) | 8.5 | 8.1 |
| 2 | 141 (20.1) | 308 (18.8) | 20.1 | 19.4 |
| 3 | 150 (21.4) | 447 (27.3) | 24.7 | 25.4 |
| 4 | 370 (52.7) | 734 (44.9) | 46.7 | 47.1 |
IP = inverse probability, IQR = interquartile range, Pao2/Fio2 = ratio of Pao2 over the corresponding Fio2.
Pao2/Fio2 was only assessed in patients receiving invasive mechanical ventilation.
Inflamed was defined as at least one of the following on ICU days 1 or 2: C-reactive protein > 100 mg/L or ferritin > 1,000 ng/mL. Noninflamed was defined as at least one value below the thresholds above. The thresholds above were selected based on prior studies (29–31).
Regional density of coronavirus disease 2019 (COVID-19) was assessed by categorizing hospitals into quartiles according to the regional (county) density of COVID-19 cases present on the median date of ICU admission for the patients who were contributed by that hospital.
Data regarding body mass index were missing for 23 proned patients (3.3%) and 73 nonproned patients (4.5%). Data regarding WBC count were missing for 30 proned patients (4.3%) and 56 nonproned patients (3.4%). Data regarding inflammation were missing for 70 proned patients (10.0%) and 232 nonproned patients (14.2%).