Intraoperative Multimodal Monitoring as a Means in Reducing the Duration of Mechanical Ventilation in High-Risk Patients Undergoing Major Abdominal Procedures - A Pilot Study

This study will include patients aged 50 and older scheduled for elective abdominal oncologic surgery, classified as ASA II and III due to increased anaesthetic and surgical risk. Gender will not be a stratification factor. Exclusion criteria include patient refusal, memory impairment, psychosis, known or suspected EEG abnormalities, chronic psychoactive medication use, urgent procedures, BMI below 18 kg/m² or above 35 kg/m², persistent arrhythmias, NYHA class III-IV heart failure, valvular disease, liver diseases, and anticipated surgery duration over six hours. Eligible patients must sign an informed consent form one day prior to surgery. Demographic data collected will include age, sex, operation type, comorbidities, ASA status, height, weight, and BMI. Randomisation will occur before the study begins with a sample size of 100 subjects based on a pilot study of 5 patients per group. Premedication and Monitoring: Patients will receive premedication per institutional protocol, which includes intramuscular midazolam. Intraoperative monitoring follows randomisation allocation. The control group will have standard measurements, including invasive pressure and ECG. Data collection will be handled by designated team members who will archive anaesthesia charts. After intubation, patients will be ventilated with 6-8 ml/kg of predicted body weight and a fresh gas flow of 1 L/min. Intervention Group Protocol: In the intervention group, monitoring will be established via radial artery cannulation under local anaesthesia, using LiDCOrapid®, Rainbow®, and Hb attachments. Baseline MAP and CO values will be recorded, with DO2 calculated automatically. Sensors will be positioned to monitor anaesthetic depth and rSO2 before pre-oxygenation. A noradrenaline infusion will maintain venous tone. Anaesthesia will use TCI with propofol and sufentanil, targeting specific values based on age groups. The primary goal is to maintain an rSO2 of at least 85% of baseline. If rSO2 falls belo