Background: Accurate prediction of fluid responsiveness in mechanically ventilated ICU patients remains challenging, particularly under protective low tidal volume ventilation, where static and dynamic indices often fail. This study aimed to evaluate the efficacy and correlation of carotid (ΔVpeak-CCA) and LVOT (ΔVpeak-LVOT) peak velocity variations versus electrical cardiometry-derived SVV during tidal volume challenge (TVC) for predicting fluid responsiveness. Patients and Methods: Thirty prospective observational study included 50 mechanically ventilated ICU patients at Benha University Hospitals. TVC entailed increasing tidal volume from 6 to 8 mL/kg ideal body weight for 2 minutes. ΔVpeak-CCA, ΔVpeak-LVOT, and SVV were measured via Doppler ultrasound and cardiometry at baseline (T1) and post-challenge (T2). Responders had SVV increase >2.5%. Results: About 44% were responders. TVC significantly increased all indices (SVV: 11.0±2.8% to 13.3±3.3%, p