SIZE OF THE STUDY AND DATA ANALYSIS CRITERIA This is a phase II study, which is exploratory and estimative and that involves randomization of all recruitable patients during the period of study all over the three centers involved in the work. The study will begin on January 2010 and will last for 3 years. The sample size has been calculated on the basis of the available data at the Post-Operative Intensive Care Unit of the Hospital in 2007: these data showed a mortality of the patients with acute abdomen undergoing abdominal surgery under emergency and presenting at the moment of arrival to Post Operative Intensive Therapy at least a sign of hypoperfusion of 30%. Assuming a two-tailed alpha level <0.05 and a power of 80%, we have calculated that 100 patients per arm are needed to detect an absolute reduction in mortality of 15%. This reduction appears to be significant from the clinical point of view considering previous trials of fluidic therapy in shocked patients . For comparisons between the means, the t-student test will be used. For comparison of events frequencies the χ2 test or Fisher's test - as indicated - will be used. A p <0.05 will be considered statistically significant. Static analysis will be performed using version 16.0 of SPSS software.