| Top principal adverse event category | Mean additional length of stay (days) | No of events in each category | Total no of extra days in hospital |
| Ongoing pain/restricted movement following back surgery | 22 | 22 | 474 |
| No, delay, inadequate investigations ischaemic heart disease | 13 | 34 | 451 |
| Wound infection following peripheral procedure | 11 | 29 | 314 |
| Incisional hernia: postprocedural | 10 | 27 | 271 |
| Postoperative bowel obstruction/adhesions | 13 | 21 | 271 |
| Injury due to fall in nursing home | 12 | 19 | 219 |
| Failed/blocked/ruptured/aneurysm, vascular grafts | 13 | 17 | 215 |
| Recurrent incisional hernia | 9 | 20 | 190 |
| Pulmonary embolism postoperatively | 8 | 22 | 185 |
| Wound infection following abdominal/retroperitoneal/pelvic procedure | 5 | 35 | 178 |
| Catheter-related urinary-tract infection | 5 | 37 | 174 |
Each of these outcome categories can arise from a wide variety of different causes.