Most ICU patients develop a positive fluid balance, mainly during the two first weeks of their stay. The causes are multifactorial: a reduced urine output subsequent to shock state, positive pressure mechanical ventilation, acute renal failure, post-operative period of major surgical procedures, and simultaneous fluid loading to maintain volemia and acceptable arterial pressure. Additionally, the efficacy of fluid loading is frequently suboptimal, in relation to severe hypoalbuminemia and inflammatory capillary leakage. This results usually in a cumulated positive fluid balance of more than 10 litres at the end of the first week of stay. A high number of studies have showed that such a positive fluid balance was an independent factor of worse prognosis in selected populations of ICU patients: acute renal failure, acute respiratory distress syndrome (ARDS), sepsis, post-operative of high risk surgery. However, little is known about the putative causal role of positive fluid balance by itself on outcome. However, in two randomized controlled studies in patients with ARDS, a strategy of fluid balance control has been demonstrated to reduce time under mechanical ventilation and ICU length of stay with no noticeable adverse effects. Although avoiding fluid overload is now recommended in ARDS management, there is no evidence that this approach would be beneficial in a more general population of ICU patients (i.e. with sepsis, acute renal failure, mechanical ventilation). In addition, fluid restriction -mainly if applied early could be deleterious in reducing both tissue oxygen delivery and perfusion pressure. There is a place for a prospective study comparing a "conventional" attitude based on liberal fluid management throughout the ICU stay with a restrictive approach aiming at controlling fluid balance, at least as soon as the patient circulatory status is stabilized. The latter approach would use a simple algorithm using fluid restriction and diuretics based on daily weighing, a common procedure in the ICU, probably more reliable than cumulative measurement of fluid movements in patients whose limits have been underlined.

Inclusion Criteria:

• Patients under mechanical ventilation, admitted for > 48h and <72h and no discharge planned for the next 24h

Exclusion Criteria:

• Age < 18 years
• Failure to weigh the patient
• Multiple trauma
• Transfer from another ICU with a previous stay > 24h
• High probability of withdrawing treatment for ethical purposes within 7 days
• Pregnancy
• Patient refusal