Effect of VExUS Ultrasound Protocol (Venous Excess Ultrasound) on Perioperative Fluid Management, on the Incidence of Postoperative Pulmonary Complications and Postoperative Acute Kidney Injury in Patients Undergoing Thoracic Surgery

The VExUS protocol is a standardized point-of-care ultrasound examination that includes measurements of the inferior vena cava (IVC) diameter, combined with Doppler analysis of waveforms in the hepatic vein, portal vein, and renal veins. From this analysis, the presence of venous congestion-classified as mild or severe-or its absence is determined. A high VExUS score (grade 3) has been strongly associated with the occurrence of acute kidney injury in patients undergoing cardiac surgery and has more recently been linked to elevated right atrial pressure (RAP ≥ 12 mmHg). The protocol includes the following classification: * Grade 0: IVC \< 2 cm * Grade 1: IVC ≥ 2 cm, with normal or mildly abnormal waveforms in the hepatic, portal, and renal veins (mild congestion) * Grade 2: IVC ≥ 2 cm, with severely altered waveforms in at least one vein (moderate congestion) * Grade 3: IVC ≥ 2 cm, with severely altered waveforms in multiple veins (severe congestion)

Intraoperatively patients of the control group will be administered isotonic crystalloids (Lactated Ringer's, Plasma-Lyte) at a rate of 3 mL/kg/h.Fluid administration will continue at a rate of 3 mL/kg/h as per standard practice in the PACU.