Brain Blood Flow and Cerebral Autoregulation Monitoring in Critically Ill Children

This study uses a non-invasive (external) ultrasound test called Transcranial Doppler (TCD) to measure how blood flows through the major arteries of the brain of children receiving care in the Pediatric Intensive Care Unit (PICU). TCD is already used for clinical reasons in many children, but it is not part of routine monitoring for every critically ill child. By using TCD, the investigators hope to better understand how brain blood flow changes during illness. They will also track children's functional status from before their illness to the time of PICU discharge to explore how brain blood flow patterns relate to neurological outcomes.125 participants will be enrolled and will be on study while in the PICU, estimated to be 3-14 days.