Per-dialytic hypotension is common in Intensive Care Unit patients under continuous renal replacement therapy, and occurs in nearly 50% of the patients. To date, there is a lack of study having characterized the underlying mechanism of hypotension in this setting. New diagnostic methods are now available with high reliability to identify hypovolemia as the underlying cause of hypotension, among which change in cardiac index during passive leg raising may be the less affected by restrictive validity criteria. A change in cardiac index greater than 10% during this test is highly predictive of preload dependence, i.e the probability than cardiac index will increase if cardiac preload increases.

The aim of this study is then to identify, among hypotensive episodes occurring during renal replacement therapy in Intensive Care Unit patients, the percentage of episodes related to preload dependence as identified by passive leg raising.

Inclusion Criteria:

• Intensive Care Unit patients with acute kidney injury
• under continuous renal replacement therapy initiated since less than 24 hours
• under hemodynamic monitoring by the PiCCO® device.

Exclusion Criteria:

• lower limb amputation
• inferior vena cava compression
• intracranial hypertension
• age below 18 year
• pregnancy
• advance directives to withhold or withdraw life sustaining treatment,
• lack of written informed consent by patient or next of kin
• lack of affiliation to social security as required by French regulation
• patient under a legal protective measure
• previous inclusion in current study
• inclusion in another research study

This study concerns patients hospitalized in intensive care unit at the Croix-Rousse hospital in Lyon with acute renal insufficiency (stage 3 of the Kidney Disease: Improving Global Outcomes classification) for which treatment with continuous hemofiltration was initiated less than 24 hours ago and for whom a hemodynamic monitoring device (PiCCO® device) has been implanted due to acute circulatory failure and is functional.