Fluid overload is a poor prognostic factor in patients undergoing continuous renal replacement therapy in critical care. A strategy of active fluid removal by net ultrafiltration (UFnet) is one of the means to correct it. However, fluid overload is difficult to quantify: weight variations or cumulative fluid balance are easy to use but imprecise and not concordant markers, while reference methods such as isotope dilution are not adapted to daily practice.

Bio electrical impedance analysis (BIA) is used to estimate body composition, including hydration. It is a non-invasive, rapid and painless measurement. It is commonly used in chronic intermittent haemodialysis to estimate dry weight and guide fluid removal, with a demonstrated impact on blood pressure control. This analysis is feasible in the ICU. Fluid overload as defined by BIA correlates with mortality, most notably in acute renal failure and during continuous renal replacement therapy.

We routinely perform multifrequency segmental BIA (InBody S10, Seoul, Korea) in patients with fluid overload in our intensive care department. Since February 2021, we have implemented a protocol to systematically correct fluid overload by inducing negative fluid balance with UFnet in a manner appropriate to tissue perfusion. In this context, we systematically perform a BIA analysis on the day of the beginning of the fluid balance negativation and then every 48 hours during the first five days.

We would like to evaluate the relevance of BIA monitoring in these patients by comparing it to other parameters of evaluation of the volume status usually used.

Inclusion Criteria:

• Age higher than 18
• Protocol directed deresucitation strategy with net ultrafiltration during continuous renal replacement therapy
• Bioelectrical impedance analysis available for the day of the initiation of the deresuscitation strategy and at day 5" -> "At least two bioelectrical impedance analysis available during the first 5 days of the initiation of the deresuscitation strategy".

Exclusion Criteria:

• Left ventricular assist device
• Patient opposition to the use of his health data
• Invalid bioelectrical impedance analysis
• Advanced directives to withhold or withdraw life-sustaining treatment

Patients with fluid overload (defined by a cumulative fluid balance > 5%), stable hemodynamic (defined by Norepinephrine equivalent < 0.5µg/kg/min and nor clinical nor biological sign of hypoperfusion) and continuous renal replacement therapy. All these patients benefit in our service from a protocol directed, perfusion based deresuscitation strategy with net ultra filtration to induce negative fluid balance.