PURPOSE:To determine if changes in blood volume during renal replacement therapy (RRT) in the form of continuous (CVVHD) or intermittent (IHD) dialysis correlate with changes in cardiac performance as measured by minimally invasive techniques.
METHODS:We measured delta blood volume (DBV) and hematocrit (HCT) in ICU patients undergoing RRT using the Crit-Line (Hemametrics, Kaysville, UT) while simultaneously monitoring cardiac index (CI), stroke volume index (SVI) and stroke volume variability (SVV) using an arterial pressure cardiac output monitor (Flo-Trac sensor/Vigileo monitoring system, Edwards Lifesciences, Irvine, CA). Pearson's correlation coefficients were calculated for DBV, CI, SVV, and SVI.
RESULTS:Patients undergoing CVVHD (n=6) had a statistically significant correlation between DBV and CI (r=0.583, p<0.001). In the IHD group (n=12) the relationship was not as strong (r=0.4026, p<0.001). Stronger correlations were also found for CVVHD vs. IHD when comparing CI and HCT (r=0.436, p<0.001 for CVVHD vs. r=0.123, p<0.001 for IHD) as well as SVI and DBV (r=0.421, p<0.001 for CVVHD vs. r=0.281, p<0.001 for IHD). When comparing variables between groups, the IHD patients had a significantly greater SVV (Mean, 16.85; 95% CI (11.08, 22.61) than CVVHD (Mean, 8.67; 95% CI (7.74, 9.60), p< 0.01).
CONCLUSION:DBV is correlated with changes in cardiac performance, especially in patients undergoing CVVHD. A greater degree of SVV is seen in patients undergoing IHD, an expected finding given the shorter duration used to achieve a similar change in DBV as CVVHD. Even though the results were significant, the impact of DBV on CI, SVV, and SVI was not as strong as anticipated. This may be due to the ability of the venous capacitance system to accommodate for changes in blood volume experienced during RRT.
CLINICAL IMPLICATIONS:Critically ill patients undergoing RRT may be able to tolerate more aggressive fluid removal before a negative impact on cardiac performance occurs. Minimally invasive technology providing SVV, SVI and CI is a potential part of the equation for developing further insight into understanding volume management.
DISCLOSURE:Patrick Mailloux, No Financial Disclosure Information; No Product/Research Disclosure Information