Timing of Complications in the First 24 Hours After Admission to a Postoperative (POSTICU-24)

Design and setting This is a single-centre, prospective, observational cohort study conducted in the postoperative (surgical) intensive care unit of the Department of Anesthesiology and Reanimation of a tertiary training and research hospital. Population Consecutive adult patients (>=18 years) admitted to the ICU for postoperative monitoring after elective or emergency surgery will be enrolled. No study-specific intervention is performed; all patients receive standard clinical care. All data are extracted from routinely collected clinical records: patient charts, anaesthesia records, ICU observation forms, hourly nursing charts, monitor recordings and laboratory results. Time definition The moment of ICU admission is defined as hour 0. All patients are followed from this reference point. Systematic assessments are performed at 0-2, 2-6, 6-8, 8-12 and 12-24 hours. In addition, hourly nursing and monitor records are used to determine the timing of each complication as precisely as possible (hour and, where available, minute level). For every complication, the time of first onset is recorded separately. Data collected Demographic and preoperative data (age, sex, height, weight, body mass index, ASA physical status, comorbidities, preoperative laboratory values, chronic medication); intraoperative data (surgical specialty and procedure type, elective vs emergency status, duration of surgery, anaesthetic technique, intraoperative hypotension or arrhythmia, fluid and blood product administration, vasopressor/inotrope requirement, extubation status); and postoperative ICU monitoring parameters recorded within each time window (heart rate, mean arterial pressure, vasopressor/inotrope use and dose changes, SpO2, respiratory rate, mode of oxygen therapy, mechanical ventilation status, reintubation, hourly urine output, serum creatinine, level of consciousness, sedation/agitation level, delirium assessment where applicable, arterial blood gas, haemoglobin/haematocrit, troponin and lactate where available). Complication assessment Complications are assessed against predefined objective criteria. Only events that are clinically significant and/or require intervention are recorded as complications. For each complication, the time of first onset, the diagnostic criterion applied, the requirement for clinical intervention and whether the event was recurrent are recorded separately.

Where a patient develops more than one complication, each is recorded as a separate event and the time of the first complication is additionally analysed. Predefined complication categories are: acute kidney injury, cardiac arrhythmia, respiratory complications, haemodynamic instability, neurological complications, bleeding and transfusion requirement, and infectious complications. Complication severity is graded using the Clavien-Dindo classification. Complication types, timing of onset and early-window complication rates are analysed separately for each group. 7. Study Design Study Type Observational Observational Study Model Cohort be calculated for the 0-6, 0-8, 8-12 and 12-24 hour windows. Early complication development (first 6-8 hours) will be defined as a binary variable and its capacity to represent the total complication burden will be analysed. Independent risk factors will be identified by logistic regression, with Cox regression where time-dependent effects require assessment. Results will be reported with odds ratios and 95% confidence intervals. Ethics The study will be conducted in accordance with the Declaration of Helsinki and the principles of Good Clinical Practice. All data will be anonymised. The study involves no additional intervention and poses no risk to participants.