Background The cardiac preload evaluation is essential, but the usual manometric measurements (CVP and PAOP) are inexact and they may lead to mistakes. Functional hemodynamic monitoring (FHM) has advantages and a stronger physiological basis to predict response to fluids, but it isn’t well known how it is affected by tidal volume (VT) and lung compliance (LC).

Objective to determine the effect of VT on pulse pressure variation (PPV) and systolic volume variation (SVV) in normal and reduced LC conditions.

Method 41 piglets (4.8±0.35 kg) were anesthetized and mechanically ventilated with a specific protocol. They were instrumented with a central venous catheter and pulse-contour analysis PiCCO® catheter (Pulsion, Germany). ARDS was induced with tracheal instillation of 10% Tween 20 solution. PPV and SVV were measured with VT of 6 and 12 mL/kg, before and after ARDS induction. Data are expressed as mean±SD. The ANOVA test was performed. A p-value <0.05 was considered significant.

Results The LC was 1.58±0.60 at baseline and 0.93±0.24 mL/cm H₂O/kg after ARDS induction (p<0.001). VT did not affect FHM under normal LC, but it did with reduced LC (see tables 1 and 2).

Conclusion

VT influences FHM when lung elastic properties are decreased. This probably reflects cyclic alterations of cardiac preload (cava vein collapse) and afterload (greater alveolar capillaries resistance) during inspiration. As shown in this data, VT and LC must be considered when deciding fluid administration.

Funding sources: Fondecyt 11075041.