Packed Red Blood Cell Transfusion and Intestinal Blood Flow in Preterm Neonates

The purpose of the study is to determine whether packed red blood cell (PRBC) transfusion affects intestinal blood flow of premature infants during feedings and if so, whether return of normal intestinal blood flow pattern occurs within 48 hours of blood transfusion. Abnormal intestinal responses to the feedings (insufficient postprandial blood flow increase in order to digest given feeding volume or overall decrease of intestinal blood flow) may predispose infants to feeding intolerance and to serious intestinal disease called necrotizing enterocolitis (NEC). Patent ductus arteriosus (PDA) is a relatively common heart condition found in young preterm infants that can lead to decreased blood flow in different organs, including intestines. Thus, the determination of the presence or absence of PDA is an important part of the study, since it can be a relevant confounding variable. In this study, the investigators will assess intestinal blood flow by using sonogram to measure velocity through the superior mesenteric artery (SMA), the artery supplying most of the intestine, both pre- and 45 minutes post feeding. The investigators will also use echocardiogram to determine the presence or absence of PDA. Each set of measurements will be done immediately before and after the transfusion, and again 24 and 48 hours after the transfusion. Specific Hypothesis: The investigators hypothesize that infants will have attenuated postprandial blood flow velocities in immediate posttransfusion state when compared to the pretransfusion values. The investigators further hypothesize that normal, pretransfusion postprandial blood flow velocities will be achieved 48 hrs after the blood transfusion.