To quantify the relationship between hemodynamics and blood volume changes during continuous renal replacement therapy(CRRT) to guide fluid management.
We measured delta blood volume(DBV) and central venous O2 saturation(ScvO2) in 10 ICU patients undergoing CRRT 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). Multivariate regression models for longitudinal data assessed the relationship between DBV on CI or SVV. Trends in the variables over time were measured by serial correlation coefficients.
In separate multivariate models, DBV was a statistically significant predictor of CI (coefficient = −0.009, p < 0.014) and SVV (coefficient = −0.134, p < 0.001) but the models’ predictive abilities were low. After adjusting for ScvO2 and SVV, a DBV ≤ −10% was associated with an increase in CI of 0.35 cc/min/m2 (p < 0.001) but had no significant effect on SVV. 50% of the patients had declining ScvO2 and DBV with higher mean CIs than their non-declining peers (3.7; 95% CI (2.4, 5.2) vs. 2.8; 95% CI (2.8, 3.0), p = 0.16). 3 patients had declining DBV and ScvO2 but stable SVV and SVI. Their mean CIs were similar to other CVVH patients but less variable (3.1; 95% CI (2.7, 3.6) vs. 3.4; 95% CI (2.1, 4.8), p = 0.65).
DBV does impact CI but its predictive ability is low. The fact CI increased with a negative DBV suggests it is possible to more aggressively remove fluid in critically ill patients undergoing CRRT. Distinct trend patterns in DBV, SVV and SVI emerged which may help identify patients suited for aggressive volume removal. These associations require more study to determine cause, effect and characteristics of specific patient populations tolerant of more aggressive fluid removal.
Hemodynamic variables allow for more precise volume titration during CRRT than DBV and it is likely clinicians can be more aggressive removing fluid from these patients.
Patrick Mailloux, No Financial Disclosure Information; No Product/Research Disclosure Information