In severely ill patients and emergencies the accurate estimation of intravascular volume is vital for guiding fluid therapy. Clinically this can be extremely difficult. Traditionally central venous pressure (CVP) is used as a guide in fluid management since it serves as a physiologic estimate of the intravascular fluid volume and the mean right atrial pressure. It is a particularly important parameter to measure in critically-ill patients who may require fluid resuscitation. However, CVP measurement requires invasive central venous catheter placement which is time consuming and may be associated with a number of complications like arterial puncture, venous air embolism, hemo/pneumothorax.

            The IVC is a large, compliant vein that carries deoxygenated blood into the right atrium. Its size and shape correlate strongly with the CVP. As it is highly compliant, the size of the IVC varies with intravascular pressure; it collapses during inspiration and dilates during expiration. In healthy subjects breathing spontaneously, cyclic changes in thoracic pressure may result in collapse of the IVC diameter of approximately 50%. The dimensions and respirophasic changes of the IVC can easily be studied by ultrasound. Ultrasonography is a quick, noninvasive, portable, easy and safe procedure for the examination of the inferior vena cava (IVC)., being a safe, nonionizing, noninvasive, portable and accessible imaging modality.

          Many studies have confirmed the association between the size of the IVC and collapsibility index (CI) with the right-sided cardiac hemodynamics and pressure. CI as a simple guide to right review hence atria pressure has also been investigated and found to be reliable.

    This study aimed to assess the diameter and CI of the IVC among criticall ill patients who require non-invasive or invasive ventilator support in ICU.