Table 1.
Characteristics of the patients included in the cohort at admission and outcomes, considering the whole population and according to different subgroups of carbon dioxide ranges
| Total n = 1476 (100) | Forced hypocapnia (PaCO2 < 26 mmHg) n = 40 (2.7%) | Severe hypocapnia (PaCO2 26 to < 32 mmHg) n = 173 (11.7%) | Mild hypocapnia (PaCO2 32 to 35 mmHg) n = 334 (22.6%) | Normocapnia (PaCO2 > 35 to 45 mmHg) n = 804 (54.5%) | Hypercapnia (PaCO2 > 45 mmHg) n = 125 (8.5%) | P value | |
|---|---|---|---|---|---|---|---|
| Demographics at ICU admission | |||||||
| Age, years, mean (SD) | 52 (18) | 50 (18) | 52 (19) | 51 (18) | 51 (18) | 52 (19) | 0.965 |
| Gender (male), n (%) | 973 (65.9) | 22 (55) | 98 (56.6) | 206 (61.7) | 553 (68.8) | 94 (75.2) | 0.001 |
| BMI, kg/m2, mean (SD) | 26.3 (5.1) | 25.8 (5.4) | 25.9 (4.3) | 26.0 (4.7) | 26.4 (5.4) | 27.1 (5.2) | 0.198 |
| Study country, n (%) | 0.001 | ||||||
| The Netherlands | 52 (3.5) | 5 (12.5) | 5 (2.9) | 12 (3.6) | 27 (3.4) | 3 (2.4) | |
| France | 646 (43.8) | 8 (20) | 62 (35.8) | 152 (45.5) | 373 (46.4) | 51 (40.8) | |
| United Kingdom | 50 (3.4) | 0 (0) | 2 (1.2) | 10 (3) | 33 (4.1) | 5 (4) | |
| India | 78 (5.3) | 6 (15) | 17 (9.8) | 19 (5.7) | 32 (4) | 4 (3.2) | |
| Mexico | 202 (13.7) | 15 (37.5) | 41 (23.7) | 50 (15) | 82 (10.2) | 14 (11.2) | |
| Argentina | 45 (3) | 0 (0) | 1 (0.6) | 12 (3.6) | 32 (4) | 0 (0) | |
| Belgium | 20 (1.4) | 0 (0) | 1 (0.6) | 1 (0.3) | 13 (1.6) | 5 (4) | |
| Italy | 131 (8.9) | 2 (5) | 12 (6.9) | 29 (8.7) | 67 (8.3) | 21 (16.8) | |
| Uruguay | 33 (2.2) | 0 (0) | 4 (2.3) | 6 (1.8) | 21 (2.6) | 2 (1.6) | |
| Canada | 11 (0.7) | 0 (0) | 6 (3.5) | 2 (0.6) | 3 (0.4) | 0 (0) | |
| Spain | 27 (1.8) | 0 (0) | 3 (1.7) | 7 (2.1) | 15 (1.9) | 2 (1.6) | |
| Switzerland | 77 (5.2) | 3 (7.5) | 8 (4.6) | 14 (4.2) | 46 (5.7) | 6 (4.8) | |
| Greece | 33 (2.2) | 0 (0) | 1 (0.6) | 7 (2.1) | 21 (2.6) | 4 (3.2) | |
| Japan | 30 (2) | 1 (2.5) | 4 (2.3) | 5 (1.5) | 17 (2.1) | 3 (2.4) | |
| United States | 7 (0.5) | 0 (0) | 0 (0) | 2 (0.6) | 5 (0.6) | 0 (0) | |
| Other | 34 (2.3) | 0 (0) | 6 (3.5) | 6 (1.8) | 17 (2.1) | 5 (4) | |
| Medical history, n (%) | |||||||
| Pulmonary disease | 49 (3.3) | 0 (0) | 4 (2.3) | 9 (2.7) | 23 (2.9) | 13 (10.4) | < 0.001 |
| Heart failure | 43 (2.9) | 2 (5) | 4 (2.3) | 9 (2.7) | 24 (3) | 4 (3.2) | 0.919 |
| Hypertension | 436 (29.6) | 11 (27.5) | 58 (33.5) | 99 (29.7) | 232 (28.9) | 36 (28.8) | 0.805 |
| Active smoking | 324 (22.1) | 3 (7.5) | 33 (19.2) | 62 (18.7) | 194 (24.2) | 32 (25.8) | 0.025 |
| Diabetes | 179 (12.1) | 3 (7.5) | 25 (14.5) | 40 (12) | 94 (11.7) | 17 (13.6) | 0.721 |
| Malignancy | 65 (4.4) | 6 (15) | 7 (4) | 14 (4.2) | 35 (4.4) | 3 (2.4) | 0.018 |
| Neurological status at ICU admission | |||||||
| Lowest GCS motor, median (IQR) | 4 (2; 5) | 4 (3; 5) | 4 (2; 5) | 4 (2; 5) | 4 (2; 5) | 4 (2; 5) | 0.827 |
| Lowest GCS, median (IQR) | 7 (5; 9) | 7 (6; 8) | 7 (4; 8) | 7 (5; 9) | 7 (5; 9) | 7 (5; 9) | 0.984 |
| Episode of anisocoria, n (%) | 406 (27.6) | 9 (23.1) | 43 (24.9) | 95 (28.6) | 219 (27.3) | 40 (32) | 0.649 |
| Type of brain injury, n (%) | |||||||
| TBI | 715 (48.4) | 19 (47.5) | 69 (39.9) | 159 (47.6) | 394 (49) | 74 (59.2) | 0.026 |
| SAH | 264 (17.9) | 5 (12.5) | 29 (16.8) | 70 (21) | 148 (18.4) | 12 (9.6) | 0.059 |
| ICH | 509 (34.5) | 17 (42.5) | 69 (39.9) | 115 (34.4) | 268 (33.3) | 40 (32) | 0.382 |
| IS | 136 (9.2) | 3 (7.5) | 17 (9.8) | 26 (7.8) | 73 (9.1) | 17 (13.6) | 0.416 |
| CNS infection | 74 (5) | 5 (12.5) | 6 (3.5) | 20 (6) | 38 (4.7) | 5 (4) | 0.156 |
| Brain tumor | 68 (4.6) | 1 (2.5) | 16 (9.2) | 14 (4.2) | 33 (4.1) | 4 (3.2) | 0.040 |
| Other | 29 (2) | 0 (0) | 2 (1.2) | 5 (1.5) | 20 (2.5) | 2 (1.6) | 0.555 |
| Neurosurgical management in ICU, n (%) | |||||||
| ICP monitoring | 626 (42.5) | 5 (12.5) | 61 (35.3) | 143 (43.1) | 370 (46.0) | 47 (37.6) | < 0.001 |
| EVD | 428 (29) | 9 (22.5) | 56 (32.4) | 101 (30.3) | 237 (29.5) | 25 (20) | 0.132 |
| Therapeutic hypothermia | 59 (4) | 0 (0) | 6 (3.5) | 14 (4.2) | 34 (4.2) | 5 (4) | 0.747 |
| Barbiturate coma | 83 (5.6) | 0 (0) | 8 (4.6) | 24 (7.2) | 42 (5.2) | 9 (7.2) | 0.277 |
| Need for neurosurgery | 593 (40.2) | 15 (37.5) | 71 (41) | 153 (45.9) | 314 (39.1) | 40 (32) | 0.071 |
| Decompressive craniectomy | 284 (19.3) | 10 (25) | 31 (17.9) | 75 (22.5) | 146 (18.2) | 22 (17.6) | 0.383 |
| ICU events and outcomes | |||||||
| VAP, n (%) | 584 (40) | 12 (30) | 60 (35.1) | 143 (43.1) | 319 (40.2) | 50 (40.3) | 0.319 |
| Tracheo bronchitis, n (%) | 136 (9.4) | 3 (7.7) | 12 (7.1) | 29 (8.9) | 86 (11) | 6 (4.9) | 0.177 |
| ARDS, n (%) | 135 (9.3) | 1 (2.5) | 10 (5.8) | 29 (8.8) | 18 (9.8) | 17 (13.7) | 0.096 |
| Mild | 24 (17.8) | 1 (100) | 4 (36.4) | 7 (24.1) | 8 (10.4) | 4 (23.5) | |
| Moderate | 54 (40.0) | 0 (0) | 5 (45.5) | 11 (37.9) | 33 (42.9) | 5 (29.4) | |
| Severe | 57 (42.2) | 0 (0) | 2 (18.2) | 11 (37.9) | 36 (46.8) | 8 (47.1) | |
| Withdrawal life-sustaining treatments, n (%) | 85 (5.9) | 0 (0) | 12 (7.1) | 14 (4.3) | 49 (6.2) | 10 (8.1) | 0.227 |
| ICU mortality, n (%) | 94 (6.5) | 2 (5.1) | 12 (7.1) | 24 (7.3) | 48 (6.1) | 8 (6.5) | 0.942 |
| Hospital mortality, n (%) | 178 (12.1) | 6 (15) | 28 (16.2) | 41 (12.3) | 85 (10.6) | 18 (14.4) | 0.245 |
| LOS in ICU, median (IQR) | 14 (8; 24) | 12 (6.8; 16.2) | 12 (7; 23) | 15 (9; 25) | 14 (8; 25) | 14 (7; 28) | 0.099 |
| Tracheostomy required, n (%) | 409 (28.0) | 15 (37.5) | 60 (34.9) | 88 (26.5) | 212 (26.6) | 34 (27.6) | 0.138 |
LOS, lengths of stay, ICU, intensive care unit, IQR, interquartile range, SD, standard deviation, ICP, intracranial pressure, EVD, extra ventricular drainage, TBI, traumatic brain injury, SAH, subarachnoid hemorrhage, IS, ischemic stroke, ICH, intracerebral hemorrhage, CNS, central nervous system, GCS, Glasgow Coma scale, BMI, body mass index, PaCO2, arterial partial pressure of carbon dioxide; VAP, ventilator-associated pneumonia; ARDS, acute respiratory distress syndrome