A total of 136 adult patients aged 18-75 yr, classified as American Society of Anesthesiologists (ASA) physical status I-II, and scheduled for elective laparoscopic abdominal surgery with an anticipated duration of at least 1 h will be included.
Patients will be excluded if they had a history of neuropsychiatric disorders, neuromuscular disease, severe cardiovascular or respiratory disease, upper respiratory tract infection within the preceding 14 days, body mass index (BMI) >40 kg m-², alcohol or substance abuse, previous bronchospasm, anticipated difficult tracheal intubation, previous tracheostomy, laryngeal disease or surgery, ASA physical status ≥III, or an actual surgical duration of less than 1 h.
Randomization and Study Groups
Patients will be randomly allocated to one of four study groups according to surgical position and use of processed electroencephalographic monitoring:
Group TBIS: Trendelenburg position with BIS monitoring. Group T: Trendelenburg position without BIS monitoring. Group RTBIS: Reverse Trendelenburg position with BIS monitoring. Group RT: Reverse Trendelenburg position without BIS monitoring. Computer-generated randomization was used for group allocation.
Haemodynamic and respiratory variables, including systolic and diastolic arterial pressure, SpO₂, ETCO₂, peak airway pressure, and BIS values, will be recorded before and after positioning in the Trendelenburg or reverse Trendelenburg position.
Demographic and perioperative data, including age, sex, height, weight, type of surgery, duration of surgery, and duration of anaesthesia, will be collected.
Extubation and recovery times, total desflurane consumption and cumulative EEG suppression time will be recorded for all patients.
PACU discharge time, pain intensity (VAS score), cumulative morphine consumption, additional analgesic (meperidine) requirements, patient comfort, and haemodynamic variables will be assessed at 15, 30, and 60 min after PACU admission.
Delirium screening will ve performed before induction of anaesthesia, at PACU admission, at PACU discharge, and twice daily thereafter (08:00 and 20:00) from postoperative day 1 through postoperative day 3, or until hospital discharge if discharge occurred earlier. Postoperative adverse events, including nausea and vomiting, respiratory depression, bradycardia, hypotension, hypertension, shivering, and urinary incontinence, will be recorded. Intensive care unit (ICU) admission, ICU length of stay, and total hospital length of stay will also be documented.