Hemodynamic parameters to guide fluid therapy

The cornerstone of treating patients with shock remains as it has for decades: intravenous fluids. Surprisingly, dosing intravenous fluid during resuscitation of shock remains largely empirical. Too little fluid may result in tissue hypoperfusion and worsen organ dysfunction; however, over-prescription of fluid also appears to impede oxygen delivery and compromise patient outcome. Recent data suggest that early aggressive resuscitation of critically ill patients may limit and/or reverse tissue hypoxia, progression to organ failure, and improve outcome [1]. In a landmark study, Rivers et al. demonstrated that a protocol of early goal-directed therapy reduces organ failure and improves survival in patients with severe sepsis and septic shock [2]. Similarly, a protocol to optimize preload and cardiac output in patients undergoing major surgery reduced postoperative complications and length of stay [3]. Uncorrected hypovolemia, leading to inappropriate infusions of vasopressor agents may increase organ hypoperfusion and ischemia [4]. However, overzealous fluid resuscitation has been associated with increased complications, increased length of intensive care unit (ICU) and hospital stay, and increased mortality. A review of the ARDSNet cohort demonstrated a clear positive association between the mean cumulative daily fluid balance and mortality [5]. Murphy and colleagues demonstrated a similar finding in patients with septic shock [6]. Data from the "VAsopressin in Septic Shock Trial" demonstrated that the quartile of patients with the highest fluid balance at both 12 hours and 4 days had the highest adjusted mortality [7]. The extravascular lung water index (EVLWI) can be accurately "measured" in critically ill patients by using the single indicator transpulmonary thermodilution method) [8,9]. The EVLWI appears to be a useful tool to quantify "capillary leakiness" and the degree of interstitial edema [10]. A number of authors have demonstrated a positive relationship be