Background: Assessment of intravascular volume status continues to be one of the biggest challenges in the management of critical care. Aim: To evaluate the efficacy of internal jugular vein (IJV)- collapsibility index in prediction of fluid responsiveness and assessment of volume status in correlation with inferior vena cava (IVC)-collapsibility index and invasively monitored central venous pressure (CVP) in ICU sepsis patients. Patients and methods: This Prospective observational study was conducted on 30 patients who admitted to the ICU with central venous catheter at Intensive care unit in Suez Canal University hospitals from January 2021 to November 2022. Results: There was a significant decrease in Internal Jugular Vein Collapsibility Index (IJC-CI) and CVP after fluid resuscitationp value <0.001, with a mean decrease of 46.50 compared to 48.80. A negative correlation was found between IVC-CI and IJV-CI p= 0.017, 0.040. The inferior vena cava collapsibility index was found to be the most effective in predicting fluid responsiveness in dehydrated patients, with a sensitivity of 84.62% and specificity of 76.47%. Central venous pressure and internal jugular vein collapsibility index were not significantly effective. Conclusion: The inferior vena cava collapsibility index is the most effective predictor of fluid responsiveness in dehydrated patients, with a sensitivity of 84.62% and specificity of 76.47%, despite a negative correlation between IVC-CI and CVP.[