Fluid Responsiveness Evaluation by a Non-invasive Method in Children, Extended to PREterm Infants - FRENCH-PREMA

Inclusion Criteria: * Premature newborn under 37 weeks of amenorrhea hospitalized in neonatal intensive care * Prescription of a 10 to 20ml/kg fluid expansion (crystalloid, blood products or albumin) by the physician in charge, whose goal would be to increase cardiac output (based on clinical, biological and/or echographic criteria). Exclusion Criteria: * Acute cardiogenic pulmonary edema * Hemodynamic instability making the delay necessary for abdominal compression and ultrasonography dangerous for the patient * Non corrected congenital cardiopathy, or inferior to 15 days postoperative. Intra-abdominal hypertension or painful abdominal palpation * Abdominal surgery in the last 15 days * Supine position contraindicated or deleterious * No investigator available to assess ultrasonographic measures * Impairment of echocardiographic acoustic window or restless patient making ultrasonography impossible