Ultrasound reference values for inferior vena cava diameter and collapsibility index in critical care patients - a prospective observational study

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

The IVC is a large, compliant veinthat carries deoxygenated blood into the right atrium. Its size and shapecorrelate strongly with the CVP. As it is highly compliant, the size of the IVCvaries with intravascular pressure; it collapses during inspiration and dilatesduring expiration. Inhealthy subjects breathing spontaneously, cyclic changes in thoracic pressuremay result in collapse of the IVC diameter of approximately 50%. The dimensions andrespirophasic changes of the IVC can easily be studied by ultrasound.Ultrasonography is a quick, noninvasive, portable, easy and safe procedure forthe examination of the inferior vena cava (IVC)., being a safe, nonionizing,noninvasive, portable and accessible imaging modality.

          Many studies have confirmed theassociation between the size of the IVC and collapsibility index (CI) with theright-sided cardiac hemodynamics and pressure. CI as a simple guide to rightreview hence atria pressure has also been investigated and found to bereliable.    This study aimed to assess the diameter andCI of the IVC among criticall ill patients who require non-invasive or invasiveventilator support in ICU.