Total Parenteral Nutrition Associated Cholestasis (TPNAC) and Plasma Amino Acid Levels in Neonates

Inclusion Criteria: * Newborns greater than 1500 g who enter the Intensive Care Unit and their pathology requiring total parenteral nutritional support (necrotizing enterocolitis, intestinal atresia, short bowel syndrome). * Gestational age greater than 30 weeks * Patients with normal liver function tests for their age, prior to the initiation of total parenteral nutrition. * Authorization from both parents or legal guardian for recruiting of the child into the study with consent signed form after the purpose and procedures have been explained Exclusion Criteria: * Patients with acute renal failure * Congenital liver disease, end-stage liver disease * Patients with liver damage secondary to viral or bacterial infection * Patients with liver damage secondary to drugs