Background: Differentiating fluid responders from non-responders is the primary goal when assessing critical care hypotensive patients for fluid responsiveness. Objectives: To assess the fluid responsiveness in critical care hypotensive patients using inferior vena cave (IVC) collapsibility index and correlating its effectiveness with lung ultrasound (US) and stroke volume variation (SVV) induced by passive leg raising (PLR) in prediction of fluid responsiveness. Patients and Methods: After approval of scientific and ethical committees, One hundred critical care hypotrnsive patients who were admitted to the ICU of El-Hussein University Hospital from November 2018 to March 2021 were included in the study. The following were done: echocardiography on admission, routine hemodynamic monitoring, lung US for assessment for extra volume lung water (EVLW), assessment of IVC variability, assessment of SVV induced by passive leg raising. Patients were classified into fluid responders and non-responders based on SVV. Responders were patients with SVV ≥ 12%. Results: Caval index for assessment of fluid responsiveness is strongly correlated with lung US for assessment of EVLW and SVV with highest sensitivity and specificity in mechanically ventilated patients on muscle relaxant, and lower sensitivity and specificity in spontaneously breathing patients. Conclusion: Caval index can be used to predict fluid responsiveness, but with different values depending on mechanical ventilation status and use of muscle relaxation.