Inferior Vena Cava Diameter as a Predictor of Mortality in Septic Shock

Abstract

Inferior Vena Cava (IVC) diameter and collapsibility index are non-invasive measurements commonly used in the assessment of intravascular volume status in critically ill patients in the intensive care unit (ICU). Information regarding the prognostic utility of IVC diameter in septic shock (SS) patients is scarce. We sought to determine the role of IVC diameter in predicting 90 day mortality in patients admitted to the ICU with SS and its association with central venous pressure (CVP). METHODS: We retrospectively evaluated 248 consecutive patients who were admitted to the ICU with SS from January 2011 to April 2013. Comprehensive baseline demographic, clinical and echocardiographic data were obtained. The association between CVP and death at 90 days was evaluated with univariate analysis. Multivariate regression analysis was used to identify clinical and echocardiographic predictors of 90-day mortality. Repeat multivariate analysis was then utilized to identify parameters associated with enlarged IVC size. RESULTS: Among the 248 patients (mean age, 64.9 AE 18 years; 51% men), baseline demographics were similar between survivors and deceased patients. Multivariate analysis revealed enlarged IVC diameter to be an independent predictor of mortality at 90 days (enlarged versus normal: OR: 2.02, 95% CI: 1.05-3.85, p<0.05). Patients with enlarged IVC size were found to be older (68 vs 63; p<0.05), have higher CVP on admission (12 mmHg vs 9 mmHg; p<0.05), initial WBC (18k vs 13.5k; p<0.05), intubation (62% vs 40%, p<0.05), RA pressure (13 mmHg vs 7 mmHg; p<0.05), and systolic pulmonary artery pressure (45 mmHg vs 35 mmHg; p<0.05). They were also found to have lower LV ejection fraction (46% vs 55%; p<0.05), cardiac index (2 vs 2.3; p<0.05) and urine output within first 24 hours (505cc vs 754cc; p<0.05). Intravenous fluid balance within the first 24 hours was similar between patients with enlarged and those with normal IVC diameters (2413cc vs 2420cc, p¼0.99). Multivariate analysis revealed CVP to be a predictor of enlarged IVC size (OR 1.18, 95% CI: 1.03-1.35, p<0.05). A relationship between CVP and mortality was established using univariate analysis, whereby an initial CVP $ 12mmHg was associated with increased odds of 90 day mortality (OR 1.35; 95% CI: 1.08-1.82, p<0.05). CONCLUSIONS: Enlarged IVC diameter is a predictor of late mortality in SS patients. In these patients, IVC dilatation was not a reflection of increased IV fluid resuscitation. Instead, it was associated with an overall worse clinical status as evidenced by worse signs of SS and end organ damage. CVP is a predictor of enlarged IVC diameter and an initial CVP $ 12mmHg confers increased late mortality in SS patients. Further studies with larger sample size are needed to account for potential confounding factors.