Cerebral Circulation in Critically Ill Children

Inclusion Criteria: Neonates and children from 0 to 18 years old hospitalized in pediatric intensive care unit (PICU) with hemodynamic failure requiring vasoactive or inotropic treatment. This includes : * shock (tachycardia, troubles of peripheral perfusion with capillary refill time \>3 sec, oliguria, with or without alteration of consciousness or arterial hypotension) * isolated arterial hypotension if it needs medical treatment to readjust balance between oxygen demand and oxygen consumption Exclusion Criteria: * primitive cerebral lesion: traumatic or neurosurgical (including brain death states) * preterm neonates of less than 37 weeks gestational age * patients already receiving more than one catecholamine * patients too instable, defined by a respiratory instability (pulse oxymetry of less than 80% during more than 5 minutes) and/or hemodynamic instability (variability of blood pressure and heart rate of more than 50%) and/or cardiorespiratory arrest.