Carotid Doppler Changes After Passive Leg Raising for Prediction of Post-Induction Hypotension in Gastrointestinal Tumor Surgery

Inclusion Criteria:

* Adults aged 18 years or older
* Patients scheduled for elective gastrointestinal tumor surgery
* Surgery planned under general anesthesia
* Body mass index (BMI) \<40 kg/m²
* Written informed consent provided

Exclusion Criteria:

* Refusal to participate or inability to obtain written informed consent
* BMI ≥40 kg/m²
* Pregnancy
* Emergency surgery
* Difficult intubation
* ASA physical status ≥IV
* Pediatric patients (\<18 years)
* Inability to perform carotid Doppler measurements
* Arrhythmia other than continuous sinus rhythm or uncontrolled cardiac arrhythmia
* Severe cardiac dysfunction or left ventricular ejection fraction \<40%
* Severe valvular heart disease
* Clinically significant autonomic nervous system disorders
* Inadequate noninvasive blood pressure monitoring or inability to obtain the required hemodynamic measurements
* Active sepsis or systemic inflammatory syndrome
* Severe peripheral vascular disease or significant carotid artery stenosis (\>50%)
* Severe pulmonary disease or advanced respiratory failure
* Implanted cardiac device (pacemaker/ICD)
* Baseline mean arterial pressure (MAP) \<65 mmHg
* Preoperative systolic blood pressure \>190 mmHg or diastolic blood pressure \>110 mmHg