A secondary study entitled "Effect of Blood Transfusion Practices on Cerebral and Somatic Oximetry", also known as the NIRS study, will determine differences in cerebral oxygenation and fractional tissue oxygen extraction with NIRS between high and low hemoglobin threshold groups during red blood cell transfusions. The investigators also propose to determine whether abnormal cerebral NIRS measures are a better predictor of NDI than hemoglobin alone and whether abnormal mesenteric NIRS measures are associated with the development of NEC within the 48 hours following a transfusion.