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Table 1 Characteristics of the study cohort

From: A comparison of prognostic significance of strong ion gap (SIG) with other acid-base markers in the critically ill: a cohort study

Variable Total cohort (n = 6878) Survivors (n = 5954) Non-survivors (n = 924, 13.4 %) p valuea
Age, years (IQR) 54.4 (38–69) 53.2 (36–67) 62.9 (48–75) 0.001
Male, no. (%) 4504 (66) 3930 (66) 574 (62) 0.023
ICU admission source, no. (%) 0.001
- Operating theatre 3166 (46) 2919 (49) 247 (27)  
- Emergency department 1813 (26) 1508 (25) 305 (33)  
- Ward 574 (8) 422 (7) 152 (16)  
- CCU/HDU 286 (4) 213 (4) 73 (8)  
- Other hospital 930 (14) 806 (14) 124 (13)  
- Other hospital ICU 55 (1) 42 (1) 13 (1.4)  
Elective surgery, no. (%) 1881 (27) 1798 (30) 83 (9) 0.001
Ward stay before ICU, days (IQR) 5 (2–10) 5 (2–10) 4 (2–13) 0.958
Mechanical ventilation on adm (%) 5412 (79) 4677 (79) 735 (80) 0.383
Acute renal failure on adm, no. (%)b 392 (6) 185 (3) 207 (22) 0.001
Worst 24-h APACHE II score (IQR) 17.0 (12–22) 16 (12–21) 27 (21–32) 0.001
SAPS III score (IQR) 43 (34–54) 41 (33–50) 60 (51–68) 0.001
SAPS III predicted risk, % (IQR) 7.9 (3–22) 6.3 (2–16) 32.8 (17–49) 0.001
MPM0 III predicted risk, % (IQR) 15.7 (8–31) 13.9 (7–26) 41.5 (22–68) 0.001
ICU stay, days (IQR) 3 (2–6) 3 (2–6) 4 (2–7) 0.001
Hospital stay, days (IQR) 13 (7–25) 14 (8–26) 6 (3–17) 0.001
Chronic medical conditions (%)b
- Respiratory 314 (5) 264 (4) 50 (5) 0.203
- Cardiovascular 679 (10) 579 (10) 100 (11) 0.313
- Liver 167 (2) 127 (2) 40 (4) 0.001
- Renal 323 (5) 244 (4) 79 (9) 0.001
- Immune disease 69 (1) 51 (0.9) 18 (2) 0.004
- Immune treatment 252 (4) 185 (3) 67 (7) 0.001
- Metastatic cancer 93 (1) 71 (1) 27 (2) 0.008
- Lymphoma 39 (0.6) 25 (0.4) 14 (2) 0.001
- Leukaemia/myeloma 83 (1) 53 (0.9) 30 (3) 0.001
- AIDS 7 (0.1) 3 (0.05) 4 (0.4) 0.008
Major admission diagnoses, no. (%)
 Cardiac or respiratory arrest 345 (5) 182 (3) 163 (18) 0.001
 Pneumonia 265 (4) 23 (4) 42 (5) 0.233
 Septic shock 36 (6) 324 (5) 112 (12) 0.001
 Multiple trauma 491 (7) 455 (8) 36 (4) 0.001
 Isolated head trauma 620 (9) 526 (9) 94 (10) 0.195
 Intracranial haemorrhage 235 (3) 154 (3) 81 (9) 0.001
 Drug overdoses 449 (7) 441 (7) 8 (0.9) 0.001
 Congestive heart failure, ischaemic heart disease or cardiogenic shock 179 (3) 129 (2) 50 (5) 0.001
 Peripheral vascular disease or aortic aneurysm 205 (3) 184 (3) 21 (2) 0.211
 GI obstruction or perforation 161 (2) 134 (2) 27 (3) 0.200
 Aspiration pneumonia 76 (1) 68 (1) 8 (0.9) 0.611
 Obstructive airway disease 136 (2) 127 (2) 9 (1) 0.015
 Heart valve surgery 516 (8) 503 (8) 13 (1) 0.001
 Coronary artery bypass graft surgery 982 (14) 958 (16) 24 (3) 0.001
 Acute lung injury or ARDS 27 (0.4) 22 (0.4) 5 (0.5) 0.398
 Gastrointestinal bleeding 125 (2) 106 (2) 19 (2) 0.511
 Pulmonary embolism 22 (0.3) 16 (0.3) 6 (0.6) 0.106
  1. All values are median and interquartile range (IQR) in parenthesis unless stated otherwise
  2. Adm admission, GI gastrointestinal, APACHE Acute Physiology and Chronic Health Evaluation, ARDS acute respiratory distress syndrome, CCU coronary care unit, HDU high dependency unit, ICU intensive care unit, MPM 0 III Mortality Prediction Model on admission, SAPS Simplified Acute Physiology Score
  3. a p values generated by either Mann-Whitney or chi square test
  4. bAccording to the definitions by the APACHE model