Necrotizing enterocolitis among neonates in the United States

Neonatal necrotizing enterocolitis: an update

Necrotizing enterocolitis (NEC) is a leading cause of mortality and morbidity in neonatal intensive care units. Here we review selected manifestations of NEC, risk factors involved in its pathophysiology as well as putative mechanisms associated with how an immature gut might be more susceptible to NEC. Treatment and potential preventive strategies are discussed.

Increased incidence of necrotizing enterocolitis in premature infants born to HIV-positive mothers

OBJECTIVE

To examine if being born to an HIV-positive mother may increase the risk of necrotizing enterocolitis in premature infants.

DESIGN

Case-control study.

SETTING

Neonatal unit of a level 3 perinatal centre.

METHODS

: Over a period of 8.5 years, all cases of necrotizing enterocolitis occurring in premature infants admitted to the neonatal unit were identified. For each case, two controls were retrospectively chosen that matched for postmenstrual age at birth, intrauterine growth and year of birth. Perinatal characteristics were studied in all infants.

MAIN RESULTS

There were 79 cases of necrotizing enterocolitis, which were compared with 158 controls. Using multivariate analysis, multiple pregnancy [odds ratio (OR), 2.29; 95% confidence interval (CI), 1.23-4.25; P = 0.009], abnormal umbilical artery velocity (OR, 2.21; 95% CI, 1.08-4.54; P = 0.030), abnormal fetal heart rate (OR, 2.14; 95% CI, 1.05-4.36; P = 0.036) and HIV-positive mother (OR, 6.63; 95% CI, 1.26-34.8; P = 0.025) were significantly more frequent in fetuses who subsequently developed necrotizing enterocolitis.

CONCLUSIONS

This preliminary report suggests an association, not previously reported, between maternal HIV-positive status and an increased risk of necrotizing enterocolitis in premature infants. Despite the limitations of this study, we suggest that premature newborn infants of HIV-positive mothers should be monitored very carefully for a possible increased risk of necrotizing enterocolitis.

Human torovirus: a new virus associated with neonatal necrotizing enterocolitis

AIM

Toroviruses have been associated with gastroenteritis in both animals and humans. The aim of this study was to examine the fecal excretion of torovirus in infants with necrotizing enterocolitis (NEC).

METHODS

We reviewed all infants with NEC admitted to our tertiary care NICU over a 5-y period who had stool specimens sent for microbial culture and virology. Infants in the NICU during the same period with diagnoses other than NEC served as controls.

RESULTS

Forty-four infants with NEC stages I-III were identified, and pathogenic organisms were identified in 27 (61%). Toroviruses were identified in stool cultures in 48% of patients with NEC, and 17% of the non-NEC controls (p<0.001). There was no significant difference in illness severity or mortality between the torovirus-positive and -negative infants with NEC.

CONCLUSION

Torovirus should be added to the list of infectious agents associated with NEC in newborn infants. The exact role torovirus plays in the etiology and progression of NEC warrants further investigation.

Assessing the Neonatal Safety of Indomethacin Tocolysis

OBJECTIVE

To systematically review and summarize the medical literature regarding the effects of tocolysis with indomethacin on neonatal outcome.

DATA SOURCES

We supplemented a search of entries in electronic databases with references cited in original studies and review articles to identify studies pertaining to indomethacin tocolysis and neonatal outcome.

METHODS OF STUDY SELECTION

We evaluated, abstracted data, and performed quantitative analyses in studies assessing the neonatal outcomes of patients undergoing tocolysis with indomethacin. Observational studies and randomized trials were included in this systematic review.

TABULATION, INTEGRATION, AND RESULTS

Forty-six studies were identified, 28 of which met criteria for systematic review and meta-analysis. These 28 studies included 6,008 infants. Of these infants, 1,621 were exposed to indomethacin for tocolysis antenatally; 4,387 infants not exposed to indomethacin served as the comparison group. An estimate of pooled odds ratios with 95% confidence intervals was calculated for dichotomous outcomes using random- and fixed-effects models. Observational studies and randomized trials were analyzed separately. Pooled estimates from observational studies and randomized trials revealed no significant differences in the rates of intraventricular hemorrhage, patent ductus arteriosus, necrotizing enterocolitis, or neonatal mortality between infants exposed to indomethacin antenatally and those not exposed. Meta-analysis of randomized trials revealed increased risk of bronchopulmonary dysplasia. However, the meta-analysis included only 3 randomized clinical trials, one of which showed increased risk. An association of bronchopulmonary dysplasia and indomethacin use was not noted in our analysis of observational studies.

CONCLUSION

Although our pooled results did not identify significantly increased risks of adverse effects, the limited statistical power of published randomized trials does not allow us to exclude the possibility that indomethacin tocolysis increases the risk of adverse neonatal outcomes.

Feeding strategies and necrotizing enterocolitis

PURPOSE OF REVIEW

To update clinical trials concerning feeding strategies or feeding interventions to prevent necrotizing enterocolitis (NEC).

RECENT FINDINGS

The overall incidence of NEC remains unchanged. Several studies have shown that it is safe to use small feeding volumes early in life even in selected circumstances, such as feeding during the use of indomethacin to treat symptomatic patent ductus arteriosus. Although descriptive case reports have linked some feeding interventions such as thickened feedings to NEC, there is no evidence to establish a causal relation. Interestingly, one report showed that neither the presence of-nor characteristics of-gastric residuals was helpful to identify those infants who subsequently develop NEC. Numerous studies in animals show that vascular and host defense responses are not adequate in the immature gut. A few small clinical trials showed that various feeding strategies may alter these responses in preterm infants. However, larger clinical trials around these issues await further characterization of the mechanisms that regulate these two aspects of gastrointestinal function with respect to feeding.

SUMMARY

Studies continue to demonstrate how fragile the immature gut is, but further work directed to understanding the mechanisms that regulate gastrointestinal responses to feeding is needed to design meaningful interventions for large prospective trials.

Tight junctions, leaky intestines, and pediatric diseases

BACKGROUND

Tight junctions (TJs) represent the major barrier within the paracellular pathway between intestinal epithelial cells. Disruption of TJs leads to intestinal hyperpermeability (the so-called "leaky gut") and is implicated in the pathogenesis of several acute and chronic pediatric disease entities that are likely to have their origin during infancy.

AIM

This review provides an overview of evidence for the role of TJ breakdown in diseases such as systemic inflammatory response syndrome (SIRS), inflammatory bowel disease, type 1 diabetes, allergies, asthma, and autism.

CONCLUSION

A better basic understanding of this structure might lead to prevention or treatment of these diseases using nutritional or other means.

Increased expression and function of integrins in enterocytes by endotoxin impairs epithelial restitution

BACKGROUND & AIMS

Experimental necrotizing enterocolitis (NEC) is characterized by circulating endotoxin (lipopolysaccharide [LPS]) and impaired enterocyte migration. We hypothesized that LPS increases integrin function and cell-matrix adhesion, leading to impaired enterocyte migration in the pathogenesis of NEC.

METHODS

NEC-like intestinal injury was induced in newborn rats by hypoxia/gavage feedings, and restitution was determined by assessing bromodeoxyuridine-labeled enterocytes along the crypt-villus axis. Newborn mice were injected with 5 mg/kg LPS. IEC-6 cells were treated with LPS +/- LY294002 or wortmannin, and beta 1- and alpha 3-integrins were assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunofluorescence. Beta 1-integrin function was determined by adherence of fibronectin beads to IEC-6 monolayers. Migration of IEC-6 cells into a scraped wound was measured by time-lapse microscopy.

RESULTS

Newborn intestinal injury was associated with decreased intestinal restitution and increased alpha 3- and beta 1-integrin expression in the ileal mucosa, which also was observed after LPS injection. In IEC-6 cells, LPS caused an increase in the expression of alpha 3- and beta 1-integrins, a shift of beta 1-integrins from the cytoplasm to the plasma membrane and an increase in fibronectin bead adhesion during which beta 1-integrins accumulated underneath attached beads. These effects could be reversed with LY294002 or wortmannin, suggesting phosphatidylinositol-3-phosphate kinase (PI3K) dependence. The increased integrin-matrix adhesion by LPS led to an inhibition of enterocyte migration, which could be reversed by anti-beta 1-antibodies.

CONCLUSIONS

Enterocyte migration is inhibited by LPS through increased expression and function of alpha 3- and beta 1-integrins. Modulation of enterocyte migration via integrins may provide novel insights into the pathogenesis of NEC, in which intestinal restitution is impaired.

Oral probiotics reduce the incidence and severity of necrotizing enterocolitis in very low birth weight infants

OBJECTIVE

We evaluated the efficacy of probiotics in reducing the incidence and severity of necrotizing enterocolitis (NEC) in very low birth weight (VLBW) infants.

PATIENTS AND METHODS

A prospective, masked, randomized control trial was conducted to evaluate the beneficial effects of probiotics in reducing the incidence and severity of NEC among VLBW (<1500 g) infants. VLBW infants who started to fed enterally and survived beyond the seventh day after birth were eligible for the trial. They were randomized into 2 groups after parental informed consents were obtained. The infants in the study group were fed with Infloran (Lactobacillus acidophilus and Bifidobacterium infantis) with breast milk twice daily until discharged. Infants in the control group were fed with breast milk alone. The clinicians caring for the infants were blinded to the group assignment. The primary outcome was death or NEC (>or= stage 2).

RESULTS

Three hundred sixty-seven infants were enrolled: 180 in the study group and 187 in the control group. The demographic and clinical variables were similar in both groups. The incidence of death or NEC (>or= stage 2) was significantly lower in the study group (9 of 180 vs 24 of 187). The incidence of NEC (>or= stage 2) was also significantly lower in the study when compared with the control group (2 of 180 vs 10 of 187). There were 6 cases of severe NEC (Bell stage 3) in the control group and none in the study group. None of the positive blood culture grew Lactobacillus or Bifidobacterium species.

CONCLUSION

Infloran as probiotics fed enterally with breast milk reduces the incidence and severity of NEC in VLBW infants.

The surgical management of necrotising enterocolitis

Necrotizing enterocolitis (NEC) is the most common gastrointestinal emergency in neonates. The disease affects mainly premature neonates. The pathogenesis is still unknown but predisposing factors are prematurity, formula feeding and sepsis. The disease can lead to gangrene and intestinal perforation requiring surgery. The options for surgery are between primary peritoneal drainage or laparotomy. However, the optimum choice between peritoneal drainage and laparotomy remains controversial, particularly in low-birth-weight infants (<1000 g). Peritoneal drainage offers temporary decompression, drainage and stabilization of patients whilst awaiting surgery, or in patients too unstable to be able to tolerate surgery or anaesthesia. Those weighing >1000 g who have no associated morbidities and are clinically stable are preferentially treated by primary laparotomy. The principal surgical objectives of laparotomy in acute NEC are to control sepsis and removal of gangrenous bowel preserving as much bowel length as possible. The surgical options at laparotomy include resection with enterostomy, resection with primary anastomosis, proximal jejunostomy and "clip and drop" technique. The option exercised is influenced by the clinical status of the patient and the extent of the disease.

Necrotizing enterocolitis: the evidence for use of human milk in prevention and treatment

Necrotizing enterocolitis (NEC) is one of the diagnoses for which donor human milk is regularly prescribed. The role of human milk in both prevention and treatment of NEC has long been recognized. Human milk, whether mother's own or donor, provides significant protection against many of the known risk factors of NECas well as therapeutic protection for the infant recovering from NEC. In the absence of mother's own milk, donor human milk could be life saving to fragile preterm infants, who are at highest risk of developing NEC.

Endotoxin differentially modulates the basolateral and apical sodium/proton exchangers (NHE) in enterocytes

BACKGROUND

Maintenance of enterocyte activity during extracellular acidosis requires functional sodium/proton exchangers (NHE), which are present at both basolateral and apical surfaces. Necrotizing enterocolitis is characterized by systemic hypoperfusion, metabolic acidosis, and the apical to basolateral translocation of endotoxin (lipopolysaccharide [LPS]). We hypothesized that LPS differentially impairs NHE activity at the basolateral or apical domains of enterocytes, leading to cellular acidification, and explored the mechanisms involved.

METHODS

Experimental necrotizing enterocolitis (NEC) was induced in newborn rats using a combination of gavage feeds and hypoxia. NHE isoforms were assessed in primary and cultured enterocytes by Western blot analysis and by confocal microscopy in the presence or absence of LPS. NHE activity was detected by single-cell fluorescent ratiometric imaging with the use of the pH-sensitive dye 2', 7'-bis-(2carboxyethyl) -5-(and-6)-carboxyfluorescein.

RESULTS

In both NEC and control rats, NHE1 was basolateral and NHE3 was apical. A similar distribution was observed in polarized IEC-6 cells. LPS caused a dose-dependent reduction in basolateral NHE1 activity in IEC-6 cells, but had no effect on apical NHE3 activity. This effect could not be accounted for by reduced expression or impaired plasma membrane localization of NHE isoforms. Strikingly, LPS-mediated NHE1 impairment caused marked cytoplasmic acidification under conditions of extracellular acidosis, whereas functional NHE1 maintained cytoplasmic pH homeostasis in control cells.

CONCLUSIONS

LPS selectively impairs basolateral NHE1 but not apical NHE3, leading to cytoplasmic acidification during extracellular acidosis. This effect could mediate impaired enterocyte function after LPS translocation and suggests a mechanism leading to barrier disruption in NEC.

Anaesthetic considerations for the management of very low and extremely low birth weight infants

The opportunities for very low birth weight infants (birth weight < 1500 g) and extremely low birth weight infants (birth weight < 1000 g) to undergo surgery are increasing. These infants are prone to prematurity-related morbidities including respiratory distress syndrome, intraventricular haemorrhage, periventricular leukomalacia, retinopathy of prematurity, patent ductus arteriosus and necrotising enterocolitis. Evidence is accumulating that preterm infants are also sensitive to pain and stress. The pharmacokinetics of drugs in preterm infants is not fully understood but smaller doses of anaesthetic drugs are usually required in preterm infants compared to term infants and older children and their effects last longer due to low clearance rates and longer elimination half-lives. Key anaesthetic considerations are (i) inspired oxygen concentration that should be adjusted to avoid hyperoxia, (ii) haemodynamic parameters that should be kept stable and (iii) prevention of hypothermia by using adequate measures to keep the infants warm. These precautions must be continuously taken during the operation and the transport to and from the operating theatre.

Current issues in the management of necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is the most common surgical emergency in the neonatal intensive care unit and remains a major cause of death in neonates. Although the pathophysiology of NEC has not been completely elucidated, progress has been made in the characterization of the molecular events which may take place during an episode of ischemia. This possible initiating event is followed by a complex cascade of inflammatory mediators active in NEC: epidermal growth factor, platelet-activating factor, and, nitric oxide. Additionally, unique characteristics of the premature gut are thought to be crucial to the development of NEC. The diagnosis of NEC continues to be based on clinical and radiographic features. Several new laboratory tests are under investigation for the purposes of earlier diagnosis, but none have prevailed at this time. Both exploratory laparotomy, with intestinal resection and peritoneal drainage are widely practiced. Mortality rates remain high and have improved little over the last couple of decades. Therefore, prevention remains crucial in order to decrease the incidence of NEC. Cautious feeding regimens, the use of maternal breast milk, passive immunization, and the use of probiotics have all been suggested but not proven as possible preventive methods. Although many advances have been made, significant opportunity remains to improve our understanding of the disease process and to develop better strategies for prevention and treatment.

Patency of the ductus arteriosus in the premature infant: is it pathologic? Should it be treated?

PURPOSE OF REVIEW

The ductus arteriosus is a vessel that connects the pulmonary artery to the aorta and provides a pulmonary-to-systemic diversion during fetal life. In the vast majority of infants, the ductus arteriosus closes by 3 days of life. In some infants, especially preterm infants with lung disease, there is delayed closure of the ductus arteriosus. There has been controversy as to whether or when the ductus arteriosus should be closed by either pharmacologic or surgical methods.

RECENT FINDINGS

There have been several epidemiologic studies describing an association between a patent ductus arteriosus and the development of morbidities, such as chronic lung disease. These associations have suggested to some that a causal relationship exists between patency of the ductus arteriosus and chronic lung disease and other morbidities. However, recent metaanalyses of randomized, controlled trials of the use of indomethacin for the prevention and treatment of the patent ductus arteriosus have not documented a decrease in the incidence of these morbidities after treatment, despite success in closure of the patent ductus arteriosus.

SUMMARY

In preterm infants, patency of the ductus arteriosus may represent a normal physiologic adaptation to allow shunting from either systemic-to-pulmonary circulation (eg, in the first day of life) or from pulmonary-to-systemic circulation (eg, in the presence of severe lung disease). Therapies designed to close the ductus arteriosus are contraindicated in some settings and should not be considered a standard of care at any time until these therapies are proven to decrease long-term clinical morbidities in randomized, placebo-controlled trials.

Endotoxin inhibits intestinal epithelial restitution through activation of Rho-GTPase and increased focal adhesions

Diseases of gut inflammation such as neonatal necrotizing enterocolitis (NEC) result after an injury to the mucosal lining of the intestine, leading to translocation of bacteria and endotoxin (lipopolysaccharide). Intestinal mucosal defects are repaired by the process of intestinal restitution, during which enterocytes migrate from healthy areas to sites of injury. In an animal model of NEC, we determined that intestinal restitution was significantly impaired compared with control animals. We therefore sought to determine the mechanisms governing enterocyte migration under basal conditions and after an endotoxin challenge. Here we show that the cytoskeletal reorganization and stress fiber formation required for migration in IEC-6 enterocytes requires RhoA. Enterocytes were found to express the endotoxin receptor Toll-like receptor 4, which served to bind and internalize lipopolysaccharide. Strikingly, endotoxin treatment significantly inhibited intestinal restitution, as measured by impaired IEC-6 cell migration across a scraped wound. Lipopolysaccharide was found to increase RhoA activity in a phosphatidylinositol 3-kinase-dependent manner, leading to an increase in phosphorylation of focal adhesion kinase and an enhanced number of focal adhesions. Importantly, endotoxin caused a progressive, RhoA-dependent increase in cell matrix tension/contractility, which correlated with the observed impairment in enterocyte migration. We therefore conclude that endotoxin inhibits enterocyte migration through a RhoA-dependent increase in focal adhesions and enhanced cell adhesiveness, which may participate in the impaired restitution observed in experimental NEC.

Necrotizing enterocolitis: preventative strategies

Necrotizing enterocolitis (NEC) remains a major cause of morbidity and mortality in premature infants. Although the pathogenesis of NEC is unclear, prevention strategies have been developed based on clinical observations and epidemiologic and experimental data. Most current strategies have centered on feeding practices (eg, institution of feeds, advancement of feeds, composition of feeds, and standardization of feeding practices). Emerging strategies include amino acid supplementation, the use of platelet-activating factor(PAF) antagonists or PAF-acetylhydrolase administration, polyunsaturated fatty acid administration, epidermal growth factor administration, and the use of pre- and probiotics.