Table 1.

Included and excluded types of complications

‘Medical’	‘Surgical’
Included a priori as potentially preventable if resulting in LOS ≥4 or 30 days readmission*: Myocardial infarction Unstable angina Heart failure Cardiac arrhythmia (LOS >4 days or after discharge but ≥7 days after surgery) Cerebral stroke/transient cerebral ischaemia Delirium/psychosis Venous thromboembolic events Pneumonia/acute worsening of chronic obstructive disease Sepsis without wound infection Unexplained infection Falls Renal infection with increase in creatinine and fluid/diuretic treatment only Fluid/electrolyte derangement treated with fluids only Renal infection resulting in dialysis Mobilisation issues preventing fulfilling functional discharge criteria within 4 days or need of inhospital rehabilitation after discharge Opioid-related side effects	Included a priori as potentially preventable if resulting in LOS >4 or 30 days readmission: Hip dislocation not caused by falling Knee manipulation under anaesthesia Wound infections with antibiotic treatment Superficial infection with wound incision Deep infection with removal of prosthetic components
Included for further evaluation on preventability: Unexplained hypotension/hypertension Unexplained fainting or dizziness Unexplained dyspnoea Constipation unrelated to opioids Complications related to existing comorbidity† Any condition not fitting other descriptions	Included for further evaluation on preventability:
Excluded a priori as being potentially preventable by perioperative intervention: No recorded morbidity (LOS >4 days only) Postoperative ileus Diarrhoea Disproved venous thromboembolic event Disproved myocardial infarction Disproved wound infection Social considerations	Excluded a priori as being potentially preventable by perioperative intervention: Postanaesthetic complications Periprosthetic fracture without recorded trauma Revision due to prosthetic malfunction Other planned reoperations Systemic arterial thrombosis/pseudoaneurism
Excluded a priori due to lack of information necessary for qualified evaluation: Gastric ulcer/gastritis Urinary retention Uncomplicated urinary tract infection Pain	Excluded a priori due to lack of information necessary for qualified evaluation: Major postoperative haematoma/swelling Major intraoperative bleeding Minor wound bleeding

*Anaemia requiring blood transfusion despite no recorded major intraoperative bleed.

†For example, difficulties with vitamin K or antihyperglycaemic treatment, management of sleep apnoea.

LOS, length of stay.