Our objective was to study the response to a fluid load in patients with and without septic shock, the relationship between the response and baseline fluid distributions and the ratios of the various compartments. A total of 18 patients with septic shock and 14 control patients without pathologies that increase capillary permeability were evaluated prospectively. We used transpulmonary thermodilution to measure the extravascular lung water index, intrathoracic blood volume index and pulmonary blood volume. For the measurement of the initial distribution volume of glucose, plasma volume and extracellular water, we used dilutions of glucose, indocyanine green and sinistrin respectively. Transpulmonary thermodilution and dilutions of glucose were repeated 75 minutes after the beginning of the fluid load.The patients in the septic group had higher volumes of extracellular water (median 295 vs 234 ml/kg, P <0.001), lower intrathoracic blood volume index (median 894 vs 1157 ml/m 2 , P <0.003), higher pulmonary permeability ratios (extravascular lung water/pulmonary blood volume) (P <0.003) and higher systemic permeability ratios (interstitial/plasma volume) (P <0.04). The intrathoracic blood volume index increase after fluid loading was lower in the septic group (10 vs 145 ml/m 2). The pulmonary permeability ratios did not correlate with the systemic permeability ratios, and in the septic group, the percentage volume retained in the intrathoracic blood volumes after fluid loading did not correlate with the systemic permeability ratios. Septic shock can cause a redistribution of fluids. Fluid administration in these patients produced a minimal increase in intrathoracic blood volume, and the percentage of volume retained in this space was not correlated with the interstitial/plasma volume ratio.

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