Relationship of inferior vena cava collapsibility to ultrafiltration volume achieved in critically ill hemodialysis patients

Background: Ultrasound (US) assessment of intravascular volume may improve volume management of dialysis patients. We investigated the relationship of intravascular volume evaluated by inferior vena cava (IVC) US to net volume changes with intermittent hemodialysis (HD) in critically ill patients. Methods: A retrospective cohort of 113 intensive care unit patients in 244 encounters had clinical assessment of intravascular volume followed by US of respiratory/ventilatory variation of IVC diameter, and had HD within 24 h. IVC collapsibility index (IVC CI)=(IVCmax-IVCmin)/IVCmax*100%. Volume management was guided by clinical data plus IVC US findings. Intradialytic hypotension (IDH) was categorized by severity from none to inability to tolerate HD. Results: Linear regression correlating n-weighted proportions of encounters achieving net volume removal of ≥0.5 L, ≥1.0 L, ≥1.5 L, and ≥2.0 L strongly correlated across the range of IVC CI (R2=0.87-0.64). Sensitivity and specificity analysis showed IVC CI was a better predictor than IVCmax of achieving net ultrafiltration (UF) volumes. Mean central venous pressure, pulmonary artery occlusion pressure, and cardiac output were poor predictors by logistic regression and receiver operating curve analyses. IVC CI <20% was the approximate optimal cutoff for achieving ≥0.5 L to ≥2.0 L net UF volumes. Net volume change achieved tended to be less than recommended and may have been limited by the development of IDH. Severity of IDH did not correlate with UF rate in mL/kg/h. χ2 analysis showed pre-US clinical intravascular volume assessments had poor concordance with IVC CI categories. Conclusion: IVC US may be a useful tool for predicting whether critically ill patients will achieve volume removal with HD.