Univariate analyses before and after one-to-four matching
| Characteristics of surgery | |||||||
| Factor | Total | AE | Before matching | After 1:4 matching | |||
| Non-AE | Non-AE | ||||||
| n = 700 | n = 28 | n = 672 | P value | n = 112 | P value | ||
| Year of surgery, n (%) | 0.615 | 0.961 | |||||
| 2009–2011 | 201 (29) | 7 (25) | 194 (29) | 24 (21) | |||
| 2012–2014 | 260 (37) | 13 (46) | 247 (37) | 56 (50) | |||
| 2015–2017 | 239 (34) | 8 (29) | 231 (34) | 32 (29) | |||
| Surgical site category, n (%) | <0.001 | 0.001 | |||||
| Intrathoracic | 188 (27) | 21 (75) | 167 (25) | 40 (36) | |||
| Upper abdominal | 117 (17) | 1 (3.6) | 116 (17) | 21 (19) | |||
| Others | 395 (56) | 6 (21) | 389 (58) | 51 (46) | |||
| ASA-PS, n (%) | 0.063 | 0.29 | |||||
| 1 | 44 (6.3) | 2 (7.1) | 42 (6.2) | 11 (9.8) | |||
| 2 | 463 (66) | 17 (61) | 446 (66) | 70 (63) | |||
| 3 | 186 (27) | 7 (25) | 179 (27) | 30 (27) | |||
| 4 | 7 (1.0) | 2 (7.1) | 5 (0.7) | 1 (0.9) | |||
| Emergency surgery, n (%) | 42 (6.0) | 1 (3.6) | 41 (6.1) | 1 | 6 (5.4) | 1 | |
| Surgery duration category, n (%) | 0.374 | 0.502 | |||||
| ≤2 h | 220 (31) | 6 (21) | 214 (32) | 36 (32) | |||
| >2–3 h | 149 (21) | 5 (18) | 144 (21) | 22 (20) | |||
| >3 h | 331 (47) | 17 (61) | 314 (47) | 54 (48) | |||
| ARISCAT score category, n (%) | <0.001 | <0.001 | |||||
| Low | 204 (29) | 1 (3.6) | 203 (30) | 27 (24) | |||
| Intermediate | 325 (46) | 7 (25) | 318 (47) | 58 (52) | |||
| High | 171 (24) | 20 (71) | 151 (23) | 27 (24) | |||
| Intraoperative blood transfusion, n (%) | 107 (15) | 7 (25) | 100 (15) | 0.175 | 19 (17) | 0.414 | |
| Multiple operations within 30 days, n (%) | 40 (5.7) | 6 (21) | 34 (5.1) | 0.004 | 24 (21) | 1 | |
ARISCAT score categories: low, <26; intermediate, 26–44; high, ≥45.
ARISCAT, Assess Respiratory Risk in Surgical Patients in Catalonia; ASA-PS, American Society of Anaesthesiologists physical status.