The SHIELD trial is a single-center, randomized, controlled, parallel-group, single-blinded clinical trial investigating whether performing RIPC one day before surgery-compared to not performing RIPC-reduces postoperative neuronal injury, as reflected by the maximum serum NfL concentration within the first 2 postoperative days, in non-cardiac surgery patients at risk for postoperative delirium.

Inclusion criteria:

• patients (≥50 years) scheduled for elective non-cardiac surgery with general anesthesia
• patients at risk for postoperative delirium, defined as the presence of ≥2 of the following established risk factors: age ≥65 years, American Society of Anesthesiologists physical status classification of ≥III, Charlson Comorbidity, planned surgical duration >180 minutes, polypharmacy (regular intake of more than five medications), symptoms of depression (Patient Health Questionnaire-9 ≥10 points)

Exclusion criteria:

• patients in whom RIPC cannot be safely applied due to relevant peripheral arterial disease (defined as Fontaine stage ≥II), lymphedema, recent upper-arm surgery, trauma, or skin lesions at the arm
• patients with acute coronary syndrome (within the past month)
• patients with surgery in the previous month
• patients with intracranial surgery
• patients with pre-existing delirium
• patients with severe cognitive impairment preventing reliable delirium assessment
• patients with current treatment with sulfonamides due to potential interference with ischemic preconditioning mechanisms
• patients with previous participation in the SHIELD trial

Clinicians involved in perioperative care and laboratory staff will be blinded to group allocation.