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1454: INFERIOR VENA CAVA DIMENSIONS POORLY REFLECT CIRCULATING BLOOD VOLUME IN THE MECHANICALLY VENTILATED

Introduction/Hypothesis: Echocardiographic measurements of inferior vena cava diameter (IVCD) and variability (IVCV) have been used in an attempt to predict fluid responsiveness in multiple clinical settings, such as septic shock, cardiovascular collapse, trauma and thermal injury. Sonographer skill and site of IVC measurement, along with differences in pathophysiology and ventilator status of the subject population, have all been reported to contribute to the heterogeneity of methodological approaches and the conclusions thus obtained, and underscore the controversy over ongoing use of IVC parameters. The aim of this study was to evaluate the relationship between IVCD and IVCV in ventilated subjects compared to direct measurement of circulating blood volume (BV). Methods: This retrospective cohort study evaluated critically-ill subjects admitted to a surgical ICU from 2015-2018 who had both an echocardiogram and BV measurement obtained within a 4hour period, while receiving mechanical ventilation. BV was measured by the BVA-100 Analyzer (Daxor Corporation, NY, USA) using radiolabeled-albumin, and was defined as percent deviation from a norm categorized as hypovolemia (<0%), euvolemia (0-16%) and hypervolemia (>16%). IVCD values were stratified into three groups: <1.5cm, 1.5-2.5cm, >2.5cm; and IVCV into: <50% and >50% diameter change with respiration. Bowker’s test of symmetry was used to test the relationship between IVCD and BV, and the Cochrane-Armitage test to examine the association between IVCV and BV. Results: The cohort (n=94) had a mean age of 64±16 years; 67% were males. APACHE II was 25±6. Diagnoses included septic shock/sepsis (62%), hemorrhagic shock (9%), cardiogenic shock (18%) and cardiac disease (67%). Several subjects had more than 1 diagnosis. 27% were hypovolemic, 28% euvolemic and 39% hypervolemic. IVCD <1.5cm were hypovolemic in 42%, IVCD 1.5-2.5cm were euvolemic in 30%, and IVCD >2.5cm were hypervolemic in 62%, with a total discordance of IVCD measurements and BV of >60% (p=0.001). There was no significant association between IVCV and BV (p=0.45). Conclusions: IVCD and IVCV are poor surrogates for circulating BV in mechanically ventilated ICU subjects.