Fluid therapy is an art in the treatment of critically ill patients. To facilitate treatment and improve patient outcomes, every effort has been made to enhance the technology used for measuring relevant physiological parameters. These parameters allow us to better understand the underlying mechanisms of certain disorders. For instance, in septic shock, hemodynamic monitoring will typically present a low systemic vascular resistance and high or normal-high cardiac output. Intuitively, an understanding of pathophysiological mechanisms will eventually translate into improvements in clinical outcomes. Pulmonary artery catheters (PACs) have been widely used for several decades only because they allow clinicians to get more information regarding hemodynamic status, but without clinical evidence of improved outcomes. In response to this lack of evidence, several randomized controlled trials have been conducted to test the usefulness of PACs in improving clinical outcomes
[31–33]. Unfortunately, all these trials consistently show that PACs do no better than controls regarding patient outcomes, but they increase medical costs significantly. These disappointing results have tempered the enthusiasm for PACs, and a survey showed that the use of PACs decreased by 65% during recent decades
However, the failure of PACs in improving clinical outcomes does not mean that the measurement of hemodynamic parameters is useless. On the contrary, it reflects the limited understanding of the complex hemodynamic characteristics in critically ill patients. With the declining use of PACs, there is an increasing number of alternatives for hemodynamic monitoring. The PiCCO system is one such alternative, which integrates a wide series of both static and dynamic hemodynamic parameters through a combination of TPTD and pulse contour analysis. The PiCCO system has several advantages over a PAC. First, PiCCO is less invasive than a PAC, so that the severe complications attributable to PACs, such as a pulmonary embolism, pulmonary artery rupture and arrhythmia, are less likely to occur
. Furthermore, the arterial canalization required for PiCCO is safe and no significant adverse events for the usually used femoral site have been demonstrated
[38, 39]. Second, the PiCCO system has the unique ability to measure global end diastolic volume (GEDV) and EVLW. Multiple studies have demonstrated the superiority of GEDV over filling pressures (for example the central venous pressure and pulmonary artery wedge pressure) in estimating cardiac preload
[40–42]. EVLWI is a quantitative assessment of pulmonary edema, which has been shown to be associated with clinical outcomes, and EVLW-directed fluid therapy may be potentially useful in improving patient clinical outcomes, such as the duration of mechanical ventilation, length of stay in ICU and mortality
[43–45]. Third, PiCCO allows continuous measurement of cardiac output, which is potentially useful given the rapidly changing hemodynamic conditions in critically ill patients. Fourth, the PiCCO system is an ‘all inclusive’ hemodynamic monitor, which integrates an array of parameters. Adjusting fluid parameters by considering all aspects of cardiac performance may confer better clinical outcomes than using a single hemodynamic parameter
. However, compared with a PAC, the PiCCO device cannot monitor pulmonary artery (PA) pressure, pulmonary artery occlusion pressure (PAOP) and mixed venous oxygen saturation. Filling pressures, as previously mentioned, are not an accurate parameter of cardiac preload. Thus, PAOP measurements are not mandatory and can be replaced by GEDV to estimate cardiac preload. Furthermore, although not numerically exchangeable, mixed venous oxygen saturation can be approximated by central venous oxygenation saturation
[46–48]. Therefore, based on current knowledge, the PiCCO system appears to be superior to the PAC in hemodynamic monitoring of critically ill patients.
The current study aims to investigate the usefulness of the PiCCO system in improving outcomes for patient with ARDS and septic shock. We believe that this randomized controlled trial will provide new evidence for fluid management in critical care settings.