Consistency of Fluid Tolerance Evaluation Methods and Their Correlation With Clinical Outcomes in Patients With Shock

Inclusion Criteria: * Shock patients admitted to the ICU are defined as those with persistent hypotension (systolic blood pressure \< 90 mmHg or a decrease of ≥ 40 mmHg from the baseline blood pressure) accompanied by signs of tissue hypoperfusion. * Age ≥ 18 years old. * The patient or their legal representatives signed the informed consent form. Exclusion Criteria: * Patients with severe pulmonary circulatory disorders such as severe pulmonary hypertension and acute pulmonary embolism. * Patients with right ventricular myocardial infarction or severe tricuspid regurgitation. * Patients with severe neck trauma or deformity that affects Doppler examination of cervical arteries and veins, or those with anatomical contraindications preventing evaluation of at least one cervical artery or vein. * Pregnant or lactating women. * Patients with diseases that may interfere with abdominal ultrasound examination.