Automated Inferior Vena Cava Collapsibility Index Fluid Responsiveness in Ventilated Patients After Cardiac Surgery.

Inclusion Criteria: * 1\. Age more than18 years old. 2. Cardiac surgical patients including (coronary artery bypass graft surgery, valvular surgeries, and aortic dissection surgeries) 3. Need for decision to administer IV fluids (hypotension that require assessment and possible fluid boluses defined as a systolic blood pressure less than 90mmHg. Normotensive patients who require fluid therapy with any other manifestation of low perfusion including tachycardia, low urine output, increased core-peripheral temperature gradient, serial increase in serum lactate, and serial increase in base deficit, and normotensive). The endpoint of fluid resuscitation is return normal blood pressure Exclusion Criteria: -1. Contraindication for fluid administration including acute pulmonary edema. 2. Moderate or more tricuspid valve lesion or pulmonary hypertension (more 50 mmHg) where high central venous pressure is expected 3. Patients on hemodialysis. 4. Patient on intra-aortic balloon pump (IABP) or extracorporeal membrane oxygenation (ECMO) 5. Irregular cardiac rhythm: patients with atrial fibrillation or frequent ectopics are excluded. 6\. Patients with chest open 7. Poor echocardiography window (The images will be stored and analyzed by senior physician within the ICU certified in echocardiography)