Study aim: To compare the effect of two anesthetic maintenance techniques (total intravenous anesthesia with propofol versus inhalational anesthesia with isoflurane) on the incidence and severity of postoperative delirium in adults undergoing abdominal surgery, and to evaluate the modifying role of gender. Design: Randomized, double‑blind, parallel‑group, superiority clinical trial on 200 patients (100 per group). Randomization will be performed using balanced block randomization with concealed allocation. Settings and conduct: Population & Sampling: Adults 18-65 undergoing abdominal surgery at Imam Khomeini Hospital, Ilam. Simple random sampling, stratified by gender. Patients allocated to two equal groups of 100: TIVA (propofol) vs. Inhalational (isoflurane). Blinding: Randomized, double-blind, parallel-group trial. Patients, outcome assessors (delirium via CAM-ICU), and data analysts are blinded to group allocation. An independent anesthesiologist administers the drugs. Setting: Post-Anesthesia Care Unit (PACU), Imam Khomeini Hospital, Ilam. Participants/Inclusion and exclusion criteria: Inclusion criteria: 1. Age 18-65 and abdominal surgery candidate. 2. ASA I or II. 3. No cognitive/psychiatric, hepatic/renal, substance abuse, or drug allergy. Exclusion criteria: 1. Age <18 or >65. 2. ASA ≥III. 3. History of cognitive/psychiatric, hepatic/renal, substance abuse, or drug allergy. Intervention groups: Group 1: total intravenous anesthesia with continuous propofol infusion (100–150 µg/kg/min) and fentanyl. Group 2: inhalational anesthesia with isoflurane (0.8–1.2 MAC) plus fentanyl. Anesthesia induction is identical in both groups using propofol, fentanyl, and atracurium. Main outcome variables: Incidence of delirium , severity of delirium , time to extubation, length of stay in the recovery room, hemodynamic changes, and consumption of additional drugs.