In this prospective observational study of sepsis patients admitted in the ICU, the ePVS was independently associated with in-hospital mortality even after multivariate adjustment for other patient clinical and laboratory conditions. To our knowledge, this result is the first attempt to predict the outcome of sepsis patients admitted in the ICU using this new biological surrogate. Our result suggests that ePVS could be a promising tool to predict the prognosis of patients with sepsis.
Fluid resuscitation is important for stabilizing hemodynamic status and improving tissue oxygenation [13]. However, it is difficult to accurately estimate the required amount of fluid in patients with sepsis. Although there are several methods to calculate the volume status of patients, all have their limitations [14, 15]. The direct methods using echocardiogram, SSV, or PPV are complex and time-consuming to apply to routine practice of all patient with sepsis. Therefore, a simple and universally available tool for assessment of volume status is needed.
In patients with sepsis, impairment of microcirculation is induced by release of proinflammatory cytokines [16, 17]. Microcirculatory dysfunction induces maldistribution of microvascular blood flow, and increased endothelial permeability leads fluid leakage from the intravascular space and tissue edema [18–20]. Accumulation of water in tissue leads to tissue hypoxia, and if not corrected, it can induce organ failure and death [21, 22]. It has been suggested that ePVS, which is derived from the Strauss formula using hemoglobin and hematocrit, may reflect plasma volume shifts at the level of interstitial tissue and therefore can be used clinically to estimate the severity of the microcirculatory dysfunction in patients with sepsis and heart failure [8, 10, 11, 23].
Initially, ePVS was developed primarily to predict the prognosis of patients with heart failure (HF). In patients with HF after acute myocardial infarction, higher ePVS was significantly associated with hospitalization or cardiovascular death [7]. Furthermore, decrease in ePVS was related with decongestion due to effective treatment and associated with better cardiovascular outcome [7–9]. Recently, Chouihed et al. reported the result of PARADISE study, which consisted of not only patients with acute HF but also with inflammatory diseases. Results showed that high ePVS was significantly associated with in-hospital mortality in patients who visited emergency department (ED) for acute dyspnea [11]. In patients who visited the ED with fever, ePVS was independently associated with poor prognosis after adjusting for confounding factors [10].
In the present study, ePVS was significantly associated with in-hospital mortality and risk of RRT in critically ill patients with sepsis. A possible explanation for these results may be due to impairment of microcirculation during sepsis. As stated, microcirculatory dysfunction increases endothelial permeability, resulting to loss of protein-rich fluid from the vessel which leads to intravascular volume depletion and tissue edema. Accumulation of water in tissue leads to tissue hypoxia which is considered as a key factor in the development of organ dysfunction and death [16, 24].
The SAPS3 and SOFA score are systematic scoring systems for sepsis patients created through large-scale clinical studies and verified through various studies [1, 25]. In this study, ePVS has a similar prognostic value with SAPS3 or SOFA score in critically ill patients with sepsis. Although the in-hospital mortality AUC for ePVS (0.655) was lower than that for SAPS (0.768) or SOFA score (0.724), it was not significantly different with that for SAPS3 or SOFA score. Despite these similarities, the SAPS3 and SOFA scores were calculated using distinct, complicated formulas. Therefore, ePVS could be a simple tool to predict the prognosis of critically ill patients with sepsis.
To the best of our knowledge, this is the first study that evaluated the role of ePVS value in predicting the prognosis of critically ill patients with sepsis. However, the present study had some limitations. First, the size of this study was relatively small. Second, we did not evaluate the association between dynamic change in ePVS value and the prognosis of patients with sepsis. Although previous studies have suggested that variation of ePVS is associated with poor prognosis [8, 9], transfusion or bleeding commonly occurred after ICU admission in this study, so change in ePVS could not be evaluated. Third, correlation between the ePVS value and actual plasma volume status was not investigated. Although previous studies have reported that ePVS reflected plasma volume status, it would have been possible to provide more accurate information if the plasma volume status was measured by other methods. Therefore, additional studies need to be carried out in order to evaluate the correlation between ePVS and the actual PV value.