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Table 1 Patient characteristics and perioperative variables

From: Prediction of the development of acute kidney injury following cardiac surgery by machine learning

Variables All Training set Test set pvalue
Patient population,n 671 469 202  
Demographic data
 Age (years) 63 (53–70) 62 (53–69) 63 (53–71) 0.323
 Male, n (%) 454 (67.7) 323 (68.9) 131 (64.9) 0.307
 BMI (kg/m2) 24.8 (22.5–27.8) 24.8 (22.5–27.6) 24.8 (22.7–27.4) 0.956
 Allergy, n (%) 598 (89.1) 42 (9.0) 31 (15.3) 0.015
 ABO, n (%)
  Type A 196 (29.2) 135 (28.8) 61 (30.2) 0.715
  Type B 144 (21.5) 110 (23.5) 34 (16.8) 0.055
  Type AB 42 (6.3) 30 (6.4) 12 (5.9) 0.823
  Type O 289 (43.1) 194 (41.4) 95 (47.0) 0.174
 Smoking, n (%) 244 (36.4) 171 (36.5) 73 (36.1) 0.937
Surgery type
 CABG only, n (%) 250 (37.3) 166 (35.4) 84 (41.6) 0.128
 Valve surgery only, n (%) 347 (51.7) 246 (52.5) 101 (50.0) 0.560
 Combined CABG + valve surgery, n (%) 74 (11.0) 57 (12.2) 17 (8.4) 0.156
 Minimally invasive surgery, n (%) 336 (50.1) 237 (50.5) 99 (49.0) 0.717
Preoperative condition
 ER stay > 1 day, n (%) 59 (8.8) 42 (9.0) 17 (8.4) 0.821
 Previous cardiac surgery, n (%) 96 (14.3) 59 (12.6) 37 (18.3) 0.052
 Preoperative ventilator support, n (%) 45 (6.7) 33 (7.0) 12 (5.9) 0.603
 Preoperative IABP, n (%) 19 (2.8) 10 (2.1) 9 (4.5) 0.096
 Cardiogenic shock, n (%) 24 (3.6) 14 (3.0) 10 (5.0) 0.209
 Arrhythmia, n (%) 138 (20.6) 93 (19.8) 45 (22.3) 0.472
Medical history
 Family history of CAD, n (%) 80 (11.9) 59 (12.6) 21 (10.4) 0.423
 Diabetes mellitus, n (%) 215 (32) 152 (32.4) 63 (31.2) 0.756
 Dyslipidemia, n (%) 258 (38.5) 177 (37.7) 81 (40.1) 0.564
 HTN, n (%) 453 (67.5) 313 (66.7) 140 (69.3) 0.515
 TIA, n (%) 23 (3.4) 13 (2.8) 10 (5.0) 0.155
 Cerebrovascular accident, n (%) 39 (5.8) 27 (5.8) 12 (5.9) 0.926
 Infective endocarditis, n (%) 34 (5.1) 21 (4.5) 13 (6.4) 0.289
 COPD, n (%) 73 (10.9) 49 (10.4) 24 (11.9) 0.584
 PAOD, n (%) 17 (2.5) 13 (2.8) 4 (2.0) 0.549
 Chronic kidney disease, n (%) 207 (30.8) 136 (29.0) 71 (35.1) 0.114
 Congestive heart failure, n (%) 131 (19.5) 93 (19.8) 38 (18.8) 0.760
 Myocardial infarction, n (%) 104 (15.5) 70 (14.9) 34 (16.8) 0.531
Baseline laboratory findings
 Serum creatinine (mg/dL) 0.91 (0.71–1.16) 0.90 (0.70–1.14) 0.95 (0.73–1.28) 0.128
 eGFR (CKD-EPI: mL/min/1.73 m2) 78.0 (53.2–99.7) 80.6 (55.6–100.9) 73.0 (47.4–98.4) 0.057
 Hgb (g/dL) 13.2 (11.4–14.6) 13.3 (11.5–14.6) 13.1 (11.4–14.3) 0.403
 Preoperative LVEF (%) 62.0 (47.0–69.0) 62.0 (49.0–70.0) 61.0 (44.0–68.3) 0.323
 LVEDD (mm) 51.6 (46.0–56.0) 51.6 (46.0–56.0) 51.6 (45.0–56.0) 0.864
 Number of diseased coronary vessels, n (%)
  One vessel disease 68 (10.1) 48 (10.2) 20 (9.9) 0.896
  Two vessel disease 59 (8.8) 40 (8.5) 19 (9.4) 0.713
  Three vessel disease 255 (38.0) 175 (37.3) 80 (39.6) 0.575
 CCS Angina Score, n (%)
  Score 0 125 (18.6) 88 (18.8) 37 (18.3) 0.892
  Score 1 134 (20.0) 97 (20.7) 37 (18.3) 0.482
  Score 2 356 (53.1) 243 (51.8) 113 (55.9) 0.326
  Score 3 50 (7.5) 37 (7.9) 13 (6.4) 0.511
  Score 4 6 (0.9) 4 (0.9) 2 (1.0) 0.862
 NYHA functional class, n (%)
  Class I 113 (16.8) 84 (17.9) 29 (14.4) 0.259
  Class II 365 (54.4) 251 (53.5) 114 (56.5) 0.486
  Class III 161 (24.0) 109 (23.2) 52 (25.7) 0.486
  Class IV 32 (4.8) 25 (5.3) 7 (3.5) 0.298
 ASA Physical Status Classification, n (%)
  Class I 10 (1.5) 7 (1.5) 3 (1.5) 0.994
  Class II 119 (17.7) 84 (17.9) 35 (17.3) 0.856
  Class III 485 (72.3) 337 (71.9) 148 (73.3) 0.708
  Class IV 51 (7.6) 38 (8.1) 13 (6.4) 0.455
Preoperative medications
 Beta blockers, n (%) 297 (44.3) 212 (45.2) 85 (42.1) 0.455
 ACEi, n (%) 68 (10.1) 51 (10.9) 17 (8.4) 0.333
 ARB, n (%) 138 (20.6) 93 (19.8) 45 (22.3) 0.472
 Intravenous nitroglycerin, n (%) 20 (3.0) 14 (3.0) 6 (3.0) 0.992
 Anticoagulants, n (%) 162 (24.1) 105 (22.4) 57 (28.2) 0.106
 Steroids, n (%) 26 (3.9) 19 (4.1) 7 (3.5) 0.718
 Aspirin, n (%) 181 (27.0) 127 (27.1) 54 (26.7) 0.926
 Lipid-lowering agents, n (%) 268 (39.9) 185 (39.4) 83 (41.1) 0.690
 Dobutamin, n (%) 7 (1.0) 4 (0.9) 3 (1.5) 0.460
 OHA, n (%) 162 (24.1) 115 (24.5) 47 (23.3) 0.728
 Insulin, n (%) 39 (5.8) 22 (4.7) 17 (8.4) 0.059
Intraoperative variables
 Operation time (mins) 225.0 (190.0–270.0) 225.0 (195.0–270.0) 220.0 (180.0–261.3) 0.101
 Elective, n (%) 625 (93.1) 439 (93.6) 186 (92.1) 0.577
 Robotic technology assisted, n (%) 7 (1.0) 4 (0.9) 3 (1.5) 0.460
 Cross clamp time (mins) 44.0 (0.0–70.0) 46.0 (0.0–70.5) 40.5 (0.0–67.3) 0.179
 Perfusion time (mins) 95.0 (0.0–132.0) 97.0 (0.0–136.0) 93.0 (0.0–124.3.0) 0.096
 Lowest core temperature (°C) 33.0 (32.0–37.0) 32.0 (32.0–37.0) 34.0 (32.0–37.0) 0.704
 Cardioversion, n (%) 192 (28.6) 131 (27.9) 61 (30.2) 0.551
 Intraoperative IV fluid infusion (mL/kg/h) 11.2 (8.4–15.2) 11.0 (8.4–15.2) 11.8 (9.0–15.2) 0.302
 Intraoperative urine output (mL/kg/h) 2.2 (1.2–3.8) 2.2 (1.3–3.7) 2.2 (1.2–4.0) 0.765
 Intraoperative estimated blood loss (mL/kg/h) 2.5 (1.7–3.6) 2.5 (1.7–3.5) 2.6 (1.7–3.7) 0.547
 Cardiopulmonary bypass utilization, n (%) 471 (70.2) 336 (71.6) 135 (66.8) 0.211
 pRBC transfusion during surgery (units) 3.0 (0.0–6.0) 3.0 (0.0–6.0) 4.0 (0.0–6.25) 0.302
 FFP transfusion during surgery (units) 0.0 (0.0–3.0) 0.0 (0.0–3.0) 0.0 (0.0–3.0) 0.979
 PLT transfusion during surgery (units) 0.0 (0.0–0.0) 0.0 (0.0–0.0) 0.0 (0.0–6.0) 0.151
Time-series features (ARV)
 ARV of HR (beats/min) 3.7 (2.7–5.2) 3.7 (2.7–5.2) 3.5 (2.5–5.3) 0.979
 ARV of SBP (mmHg) 7.3 (5.9–8.7) 7.3 (5.9–8.7) 7.3 (5.8–8.9) 0.736
 ARV of DBP (mmHg) 4.7 (3.7–6.1) 4.8 (3.7–6.1) 4.6 (3.6–5.9) 0.819
 ARV of MAP (mmHg) 5.5 (4.3–6.7) 5.5 (4.3–6.7) 5.3 (4.3–6.6) 0.889
AKI according to KDIGO criteria 163 (24.3) 114 (24.3) 49 (24.3) 0.989
 Stage I, n (%) 119 (17.7) 87 (18.6) 32 (15.8) 0.399
 Stage II, n (%) 20 (3.0) 14 (3.0) 6 (3.0) 0.992
 Stage III, n (%) 24 (3.6) 13 (2.8) 11 (5.4) 0.087
  1. Data are presented as median (interquartile range) or number (%). Abbreviations: BMI body mass index, CABG coronary artery bypass grafting, ER emergency room, CAD coronary artery disease, HTN hypertension, TIA transient ischemic stroke, COPD chronic obstructive pulmonary disease, PAOD peripheral artery occlusive disease, eGFR estimated glomerular filtration rate, CKD-EPI Chronic Kidney Disease Epidemiology Collaboration, LVEF left ventricular ejection fraction, LVEDD left ventricular end-diastolic diameter, CCS Canadian Cardiovascular Society, NYHA New York Heart Association, ASA American Society of Anesthesiologists, ACEi angiotensin-converting-enzyme inhibitor, ARB angiotensin II receptor blocker, OHA oral hypoglycemic agents, IV intravenous, pRBC packed red blood cell, FFP fresh frozen plasma, PLT platelet, ARV average real variability, HR heart rate, SBP systolic blood pressure, DBP diastolic blood pressure, MAP mean arterial pressure, AKI acute kidney injury, KDIGO kidney disease improving global outcome