Lung Ultrasound Score and Inferior Vena Cava Diameter Compared to Pulse Pressure Variation

Inclusion Criteria: * Patients on mechanical ventilation (MV). * Aged more than 18 years. * Mean arterial pressure (MAP) less than 65 mmHg or systolic arterial pressure less than 90mm Hg with signs of hypoperfusion (urinary flow \< 0.5mL/kg/ h for \> 2hr , tachycardia \> 100 beats/min, or presence of skin mottling , and seurm lactate more than 2 mmol/L). Exclusion Criteria: * Cardiac arrhythmias. * Previously known significant valvular disease or intracardiac shunt. * Chest drains. * Increasing intra abdominal pressure. * Prephiral vascular disesaes. * Adult respiratory distress syndrome (ARDS) patients due to low tidal volume. * Interstitial lung disease because B-lines in these conditions are the consequence of the thickened interlobular septa characterizing fibrosis and are not modified by the state of hydration or imbibition 12 * Any contraindication for fluid administration as cardiogenic shock, acute pulmonary edema or LVEF% less than 50%. * Renal patients with oliguria and volume overload including patients on hemodialysis or patients with acute anuric renal failure. * Patients with lower extremity artery/vein thrombosis, significant lower extremity artery plaque, lower extremity artery occlusion, inferior vena cava filter implantation and lower extremity varicose veins.