Timing of Complications in the First 24 Hours After Admission to a Postoperative

The optimal duration and intensity of intensive care monitoring after surgery is largely determined by clinical experience rather than by objective, time-based evidence. This prospective observational cohort study aims to determine how frequently clinically significant complications occur in adult patients admitted to a postoperative intensive care unit (ICU), and - more specifically - when they occur during the first 24 hours after ICU admission. Patients will be followed under standard clinical care, with no additional intervention. The time of ICU admission is defined as hour 0. Complications are recorded with their exact time of first onset, and cumulative incidence is calculated for the predefined windows 0-2, 2-6, 6-8, 8-12 and 12-24 hours. The study will assess whether complications cluster in the early postoperative period (first 6-8 hours) and what proportion of the total 24-hour complication burden this early window represents. A separate analysis will determine how often patients who remain complication-free during the first 6 hours subsequently develop a new, clinically significant complication. The findings are intended to inform evidence-based decisions about the required duration of close postoperative ICU monitoring

Inclusion Criteria: * Age 18 years or older * Underwent elective or emergency surgery * Admitted to the intensive care unit for postoperative monitoring after surgery * Monitored in the ICU for at least 24 hours, or sufficient clinical data available for the first 24 hours of monitoring * Time of ICU admission and course of monitoring reliably documented Exclusion Criteria: * Age under 18 years * Pre-existing active organ failure before surgery (for example preoperative acute kidney injury, sustained arrhythmia, requirement for invasive mechanical ventilation) * Admitted to the ICU because of continuing critical illness rather than for monitoring of new postoperative complications * Already an ICU inpatient before surgery and readmitted to the ICU postoperatively * Time of complication onset cannot be reliably determined, or records are inadequate * Incomplete data for the first 24 hours of ICU monitoring * Terminal illness managed with a palliative approach