PLR applied to this group as well as other two groups. An increase of 2mmHg detected in these patients. However, this group received the conventional fluid replacement regimen of the institution of the investigators, which is 2ml/kg/hr crystalloid infusion. The blood pressure is monitorized continually in each patient from a radial artery cannula, and an infusion of noradrenaline started if mean arterial pressure persisted below 65 mmHg.The blood product replacement plan is keeping the hemoglobin level over 10 g/dL for patients with coronary artery disease and 8 g/dL for other patients.

PLR applied to this group as well as other two groups. A 2 mmHg increase at EtCO2 detected at 1st minute of PLR. The patients in this group named as study group and received a 250 ml of crystalloid bolus. These patients also received another 250 ml crystalloid bolus if mean arterial pressure is below 65 mmHg at the end of infusion.The blood pressure is monitorized continually in each patient from a radial artery cannula, and an infusion of noradrenaline started if mean arterial pressure persisted below 65 mmHg after total of 500 ml crystalloid bolus.The blood product replacement plan is keeping the hemoglobin level over 10 g/dL for patients with coronary artery disease and 8 g/dL for other patients.

Patients in this group showed no change at End tidal carbon dioxide measurement as a response to PLR and received the conventional fluid replacement regimen of the institution of the investigators, which is 2ml/kg/hr crystalloid infusion.The blood pressure is monitorized continually in each patient from a radial artery cannula, and an infusion of noradrenaline started if mean arterial pressure persisted below 65 mmHg.The blood product replacement plan is keeping the hemoglobin level over 10 g/dL for patients with coronary artery disease and 8 g/dL for other patients.

In thoracic surgical setting, restrictive fluid replacement is widely accepted. However, goal directed fluid therapies can provide a more precise and tailored fluid replacement for each patient. Although ERAS protocols emphasize otherwise, patients still arrive in the operating room with certain deficite, due to prolonged fasting or advanced age. PLR is used as a reversible fluid challenge since the blood which is pooled in the lower extremities as well as splancnic area. End tidal carbon dioxide is monitorized at each patient per American Society of Anesthesia Guideline. In this study, we aimed to assess the feasibility of end tidal carbondioxide changes as a response to passive leg raise maneuer (PLR) for preload optimization in thoracic surgical practice.

Measurement Method: EtCO₂ (mmHg) will be recorded using a side-stream capnograph integrated into the anesthesia workstation. Baseline EtCO₂ will be measured in the supine position before the PLR maneuver. The PLR maneuver will then be performed by elevating the lower extremities to a 45-degree angle while maintaining a supine upper body position. The position remained for 1 minute and the maximum level of EtCO₂recorded.

Outcome Definition: A ≥2 mmHg increase in EtCO₂ from baseline within 1 minute of PLR will be classified as a positive response, indicating fluid responsiveness. Patients with an EtCO₂ increase of <2 mmHg will be classified as non-responders.

Blood samples will be collected at baseline (preoperative), and at 24 hours postoperatively for all participants. If the patient remains hospitalized at 48 hours, an additional blood sample for urea will be collected. Serum urea (mg/dL) levels will be analyzed using standard laboratory biochemical methods.

PVI (%) will be recorded before and after PLR using Masimo Rainbow SET. Correlation between PVI values and EtCO₂-based fluid responsiveness classification (≥2 mmHg EtCO₂ increase) will be analyzed.