The influence of venovenous renal replacement therapy on measurements by the transpulmonary thermodilution technique

Abstract

Background: Use of the transpulmonary thermodilution technique has been suggested for extended hemodynamic monitoring in critically ill patients. However, many of these patients also require renal replacement therapy (RRT). Therefore, we analyzed the influence of venovenous RRT on measurement of cardiac index (CI), intrathoracic blood volume index (ITBVI), and extravascular lung water index (EVLWI).

Methods: We studied 24 consecutive critically ill patients (15 males, 9 females; age 39-81, mean 62 yr) who had received a clinically indicated 5F femoral arterial catheter (PV2015L20, Pulsion Medical Systems, Germany), which was connected to a monitor (PiCCOplus, Pulsion Medical Systems, Germany). A 12F dialysis catheter (Trilyse Expert, Vygon) was either advanced from the vena femoralis into the vena cava inferior (n = 12) or placed into the superior vena cava (n = 12). Patients continuously received heparin for anticoagulation. Hemodynamic measurements were performed in triplicate by central venous injection of saline (15 mL, <8 degrees C) during RRT, during a brief interruption in RRT (by disconnection, without retransfusion), and immediately after reconnection. Ventilator settings, fluid status, and vasoactive drugs remained unchanged.

Results: RRT was associated with significant changes in CI (mean change, -0.1 L/min/m(2), P = 0.003) and ITBVI (mean change, -18 mL/m(2), P = 0.02), whereas EVLWI was unaffected (mean change, +0.1 mL/kg, P = 0.42). The influence of RRT on CI, ITBVI, and EVLWI was not statistically different in both subgroups.

Conclusions: RRT had no clinically relevant effect on measurement of CI, ITBVI, and EVLWI in patients with sepsis and maintained cardiac output. Furthermore, the dialysis catheter tip position had no significantly different influence under these conditions.