Journal of the Medical Association of Thailand Vol 96, No 3:MARCH 2013 (SUPPL. 3) 0125-2208 96 3 2013 Mar Inferior Vena Cava Diameter and Collapsibility Index: A Practical Non-Invasive Evaluation of Intravascular Fluid Volume in Critically-Ill Patients 14 EN Prasert Thanakitcharu Marisa Charoenwut Napha Siriwiwatanakul Original Article To conduct a prospective, cross-sectional study to evaluate the IVC diameter as a guidance for estimating the volume status in critically-ill patients by bedside ultrasonography, focusing on correlations between CVP and IVC-CI and IVC diameter. Critically-ill patients who had been placed with a functioning central venous catheter were prospectively enrolled. Evaluation of intravascular volume status was performed by bedside ultrasonography to measure the IVC diameters (IVCD), both end-inspiratory (iIVCD) and end-expiratory (eIVCD). The IVC collapsibility indices (IVC-CI) were calculated by an equation and then were compared with the CVP values. Of the 70 enrolled patients, with a mean age of 63.8 + 1.9 years, 64.3% were intubated. The most common indication of ICU admission was sepsis with hemodynamic instability (80.0%). The volume status of patients was stratified by their CVP levels as hypovolemic 15.7%, euvolemic 32.9% and hypervolemic 51.4% which correspond with the IVC-CI of 45.69 + 16.16%, 31.23 + 16.77%, and 17.82 + 12.36% respectively (p < 0.001). The highest significant correlation was found between the CVP and IVC-CI (r = -0.612, p < 0.001). In addition, there was a significant correlation between CVP and iIVCD (r = 0.535, p < 0.001); and between the CVP and mean IVCD (r = 0.397, p = 0.001). The present study supported the correlation between CVP and IVC-CI. The authors conclude that the IVC-CI can provide a useful guide for noninvasive intravascular volume status assessment of critically-ill patients. Central venous pressure Inferior vena cava diameter Collapsibility index Intravascular fluid volume  Ultrasonography