Splanchnic Tissue Oxygenation During Enteral Feedings in Anemic Premature Infants at Risk for Necrotizing Enterocolitis

Overview

Necrotizing enterocolitis (NEC) is the most common gastrointestinal emergency encountered in the newborn intensive care unit and represents a significant cause of morbidity and mortality in infants born prematurely. Among possible risk factors, a strong association between elective RBC transfusions in premature infants with anemia and the subsequent development of NEC has been consistently observed (6-11). However, a significant (and increasing) number of VLBW infants with anemia are managed with erythropoiesis stimulating agents (such as Epo) and iron and do not receive RBC transfusions during their hospital stay. The present study proposes to study this particular group of VLBW infants that remain with low (\<28 %) hematocrit while receiving full enteral feedings. The investigators hypothesize that significant anemia in VLBW infants will be associated with a baseline low cerebro-splanchnic oxygenation ratio (CSOR) (\<0.75) as measured by NIRS, and that nasogastric feedings (NGF) in those particular patients will lead to further decreased splanchnic oxygenation. The investigators further postulate that CSOR values will be significantly lower among VLBW that develop NEC as compared to infants that do not.

Necrotizing enterocolitis (NEC) is the most common gastrointestinal emergency encountered in the newborn intensive care unit and represents a significant cause of morbidity and mortality in infants born prematurely. This disease complicates the management of approximately 6 - 10% of very low birthweight (VLBW) infants and can result in significant feeding intolerance, intestinal perforation and/or death despite aggressive treatment (1). The sequence of events leading to NEC appears to be multifactorial and complex (2,3). While epidemiologic studies have identified multiple factors that appear to increase an infant's risk for the development of NEC, other than prematurity, no single predictive risk factor has been clearly delineated (4,5). Among possible risk factors, a strong association between elective RBC transfusions in premature infants with anemia and the subsequent development of NEC has been consistently observed (6-11). Possible explanations for transfusion-associated NEC have been proposed: 1) the physiological impact of anemia that can initiate a cascade of events leading to ischemic-hypoxemic mucosal gut injury predisposing to NEC (10); 2) increased splanchnic blood flow following RBC transfusion leading to reperfusion injury of gut mucosa. A significant (and increasing) number of VLBW infants with anemia are managed with erythropoiesis stimulating agents (such as Epo) and iron and do not receive RBC transfusions during their hospital stay. The present study proposes to study this particular group of VLBW infants that remain with low (\<28 %) hematocrit while receiving full enteral feedings. Near Infrared Spectroscopy (NIRS) is a non-invasive, FDA approved, bedside technology that allows determination of regional oxygen saturations (rSO2) in tissues such as the gut mesentery. Using NIRS, the oxygenation status of hemoglobin in tissues located 2-4 cm below the skin can be determined and recorded continuously (12). For instance, Dave et al. used NIRS to demonstrate that splanchnic rSO2, but not cerebral rSO2, increases after feeds in the stable prematurely born infant tolerating full bolus orogastric feedings (13). Of importance, the average hematocrit in this study group was 37% (±7) and therefore these babies had no significant anemia. While no normative values exist for mesenteric rSO2 in premature infants, recent studies have explored NIRS use in determining gut hypoxia and ischemia (14). Abdominal NIRS was used to detect alterations of intestinal rSO2 and perfusion in premature piglets that developed NEC (15). In a prospective cohort study of 40 neonates with medical or surgical acute intraabdominal pathology, a cerebro-splanchnic oxygenation ratio (CSOR) of less than 0.75 predicted gut ischemia with 90% sensitivity (16). While these studies support a role for NIRS monitoring of mesenteric rSO2, it is not clear whether 1) VLBW with significant anemia have perturbations in intestinal oxygenation and perfusion, and 2) alterations in mesenteric rSO2 predict the development of NEC in VLBW infants. We hypothesize that significant anemia in VLBW infants will be associated with a baseline low CSOR (\<0.75) as measured by NIRS, and that nasogastric feedings (NGF) in those particular patients will lead to further decreased splanchnic oxygenation. We further postulate that CSOR values will be significantly lower among VLBW that develop NEC as compared to infants that do not.