Influence of veno-venous renal replacement therapy on transpulmonary thermodilution measurements

Introduction

In principle, various factors may influence the accuracy of transpulmonary thermodilution. We analyzed whether veno-venous renal replacement therapy (RRT) has impact on the measurement of cardiac index (CI), intrathoracic blood volume index (ITBVI) and extravascular lung water index (EVLWI).

Methods

With ethics approval, we studied 24 critically ill patients (nine female, 15 male) undergoing monitoring by the transpulmonary thermodilution technique for clinical indication and veno-venous RRT. All patients had a 5-F femoral arterial catheter and monitoring system (PV2015L20; Pulsion Medical Systems). Twelve patients had a femoral venous 12-F dialysis catheter in situ (Trilyse Expert; Vygon) and 12 patients had one placed in the v. cava superior. All patients received heparin for anticoagulation of the extracorporeal circuit. Measurements of CI, ITBVI and EVLWI were performed in triplicate by injecting 15 ml saline (4–6°C) through the distal port of a triple lumen central venous catheter (Certofix Trio; Braun, Melsungen) into the v. cava superior during RRT, during shortly interrupted therapy (disconnection) and immediately after reconnection.

Results

Global hemodynamics were comparable at the three time points (mean ± SD). During RRT, the CI (mean change -0.1 l/min/m², P < 0.01) and ITBVI (mean change -18 ml/m², P = 0.02) were significantly lower. However, EVLWI was not influenced by RRT (mean change +0.1 ml/kg, P = 0.42).

Conclusion

Running RRT had no clinically relevant impact on the accuracy of the measurement of CI, ITBVI and EVLWI by transpulmonary thermodilution.

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