Severe sepsis and septic shock are life threatening medical emergencies and are among the most significant challenges in critical care. Case reports and case series suggest that plasma-derived protein C concentrate may improve the outcome of patients with acquired protein C deficiency. Evidence has accumulated on the clinical relevance of the PC pathway in modulating overwhelming inflammation and preventing coagulation derangements, two key mediators of organ damage, and thus of mortality and morbidity, in sepsis. The experience collected through these studies shows that PC is safe, in that it is not associated with bleeding or severe allergic complications,and possibly useful, at least to improve the coagulation abnormalities brought about by sepsis. Unfortunately, however, all we know comes from case series or case reports or an underpowered randomized controlled study. A randomized clinical trial, adequately powered for mortality or clinically relevant outcome, is necessary to confirm PC efficacy.The aim of this study is to demonstrate that Protein C zymogen has clinically relevant implications in terms of reduction of thromboembolic events, 30 days mortality, length of intensive care and hospital stay, time on mechanical ventilation, length of ICU and hospital stay. The study will also confirm that there is no bleeding concern with the use of Protein C concentrates.The study drug will be administered in the Intensive Care Unit for 72 hours and the patients observed till ICU discharge. Telephone followup will be performed at 30 days and at one year.