In vivo validation of a new transpulmonary thermodilution method to assess global end-diastolic volume and extravascular lung water

Introduction

The downslope time (DSt) is part of the equation used to derive global end-diastolic volume (GEDV) and extravascular lung water (EVLW) from a transpulmonary thermodilution curve. DSt may be affected by recirculation phenomena of the cold indicator, as those observed in case of valvular regurgitation. Our goal was to validate a new transpulmonary thermodilution method that does not depend on DSt.

Methods

Eleven anesthetized and mechanically ventilated pigs (90 to 110 kg) were instrumented with a central venous catheter and a right (PulsioCath; Pulsion, Munich, Germany) and a left (VolumeView; Edwards Lifesciences, Irvine, CA, USA) thermodilution femoral arterial catheter. The right femoral catheter was connected to a PiCCO₂ monitor (Pulsion) and used to measure COp (cardiac output), GEDVp and EVLWp using the method based on the equation: GEDV = COp × (MTt - DSt). The left femoral catheter was connected to the EV1000 monitor (Edwards) and used to measure COe, GEDVe and EVLWe using the new method based on the equation: GEDVe = f (S2/S1) × COe × MTt, where S1 and S2 are respectively the maximum up-slopes and down-slopes of the dilution curve. One hundred and thirty-seven measurements were done during inotropic stimulation (dobutamine), during hypovolemia (bleeding), during hypervolemia (fluid overload), and after inducing acute lung injury (oleic acid).

Results

COp and COe ranged from 3.1 to 15.4 and from 3.4 to 15.1 l/minute, respectively. COp and COe were closely correlated (r² = 0.99), mean bias (± SD) was 0.18 ± 0.29 and percentage error was 7%. GEDVp and GEDVe ranged from 701 to 1,629 and from 774 to 1,645 ml. GEDVp and GEDVe were closely correlated (r² = 0.79), mean bias was -11 ± 78 and percentage error was 14%. EVLWp and EVLWe ranged from 507 to 2379 and from 495 to 2,222 ml. EVLWp and EVLWe were closely correlated (r² = 0.97), mean bias was -5 ± 72 and percentage error was 15%.

Conclusions

In animals, and over a very wide range of values, the new transpulmonary thermodilution method is as reliable as the PiCCO method to assess cardiac output, cardiac preload and lung water during inotropic stimulation, bleeding, volume loading and lung injury.