A case control study of necrotizing enterocolitis occurring over 8 years in a neonatal intensive care unit

Alterations in platelet-derived growth factor expression in the pathophysiology of necrotizing enterocolitis

BACKGROUND

Necrotizing enterocolitis (NEC) involves impaired ileal blood flow due to alterations in vascular tone control and intestinal angiogenesis. Platelet-derived growth factor (PDGF) is a mediator of normal angiogenesis in intestinal epithelium. We hypothesized that gene dysregulation during experimental NEC results in altered PDGF expression.

METHODS

Sprague-Dawley rats were randomized to groups by litter. Controls were delivered vaginally and dam-fed. NEC groups were delivered prematurely by cesarean section and subjected to an established NEC protocol. Ileum was obtained at 0, 12, 24, 48, 72, and 96 h of life from all animals (N = 108 animals). Western blot analysis was carried out for every time point, and samples were evaluated by immunohistochemistry. Antibodies against PDGF-A, PDGF-B, and their receptors, PDGFR-α and PDGFR-β, were used. Statistical analysis was performed using two-way analysis of variance with a priori P < 0.05.

RESULTS

Ileal PDGF-A concentration was higher in controls versus NEC from 24-96 h of life. Its receptor, PDGFR-α, was low in concentration in both groups at all time points. PDGF-B concentration was increased in controls at 24 and 72 h of life but decreased at the 48-h mark. Its receptor, PDGFR-β, was also low in both groups at 12 and 24 h but increased in controls at 48 and 72 h.

CONCLUSIONS

These data support our hypothesis that PDGF and PDGF receptor expression are altered in experimental NEC. Dysregulation of PDGF during intestinal maturation could contribute to the development of NEC. Further investigation into this pathway could yield new therapeutic targets for this devastating disease.

Prenatal lipopolysaccharide increases postnatal intestinal injury in a rat model of necrotizing enterocolitis

BACKGROUND

An increased incidence of necrotizing enterocolitis (NEC) has been noted in infants who are born to mothers with chorioamnionitis.

HYPOTHESIS

Our objective was to test the hypothesis that newborn rat pups born to mothers exposed to prenatal lipopolysaccharide during pregnancy would be more susceptible to intestinal injury in a rat model of NEC and that the increased intestinal injury is mediated by dysregulation of inducible nitric oxide synthase.

METHODS

Time-dated pregnant Sprague-Dawley dams were given an intraperitoneal injection of either 2 mg/kg of lipopolysaccharide or vehicle. Rat pups from each group of dams were delivered at term and placed in a rat NEC model. A subset of pups was given either vehicle or aminoguanidine. Intestines were harvested and graded for degree of intestinal injury.

RESULTS

Maternal prenatal lipopolysaccharide exposure increased the frequency and severity of intestinal injury in the neonatal rat NEC model. Treatment with aminoguanidine significantly decreased plasma nitric oxide levels. Additionally, aminoguanidine significantly decreased intestinal injury.

CONCLUSIONS

Intestinal injury observed may be mediated via nitric oxide synthase dysregulation.

Clinical predictors of necrotizing enterocolitis in premature infants

BACKGROUND

Necrotizing enterocolitis (NEC) has emerged as the most common neonatal gastrointestinal emergency, is the most common cause of death in neonates undergoing surgery, and accounts for yearly additional hospital charges in excess of $6.5 million. Prematurity is the only common variable identified in case-controlled studies exploring this disease.

OBJECTIVES

To improve the understanding of the relationship between factors related to intestinal inflammation and ischemia and the enteral feeding regimen in the context of the premature gut, thereby identifying antecedents of NEC.

METHODS

Data were collected from the medical records of 247 premature infants for this retrospective case-controlled study. Diagnosis of NEC, as defined by Bell Stages IIA-IIIB, was required for study group assignment (n = 84). Multivariate analysis techniques were used to predict the relationships between selected variables on the outcome of NEC.

RESULTS

Premature infants were 13 times more likely to develop NEC if the infant required increased respiratory support to maintain oxygenation during the early neonatal period and 6.4 times more likely to develop NEC if the infant did not receive nutritionally fortified enteral feedings of breast milk. When both factors were present, the odds of NEC increased 28.6 times when compared with infants without these factors.

DISCUSSION

The study findings extend knowledge of antecedents to NEC beyond prematurity, highlighting the role that respiratory support and nutritional fortification of enteral feedings play in the pathogenesis of this disease. Early identification of antecedents to NEC will improve critical care management of the neonate and, in turn, decrease the incidence of this devastating gastrointestinal disease. The study findings will guide further inquiry in neonatal nutrition, physiologic and metabolic functioning, and acute clinical management of the neonate.

Low mortality in necrotizing enterocolitis associated with coagulase-negative Staphylococcus infection

The aim of this study was to correlate the clinical course of necrotizing enterocolitis (NEC) with infection by coagulase-negative Staphylococcus at the onset of the illness. Records of all newborn infants developing NEC between January 1998 and December 2001 were reviewed. NEC was classified according to the criteria of Bell et al. Numeric variables were described by standard statistical methods. Comparisons between subgroups were performed by parametric statistical tests. Forty-four patients developed NEC stage II (n = 25) or III (n = 19). The incidence was 0.024% of live births in the hospital, and the mortality rate was 9%. The main risk factor was prematurity (84%). Only one-fourth of the patients had gastric residuals. A platelet count of <100,000 cells/mm3 occurred only in grade III NEC. Blood cultures were positive in 34% of the patients. The predominant organism (73%) was coagulase-negative Staphylococcus (CoNS). Neither Clostridium nor Bacteroides species were isolated. Stage II patients were maintained nothing per os (NPO) for 9 +/- 3 days and received antibiotics for 10 +/- 3 days. All of the stage III patients required an operation. In one-third of them, primary peritoneal drainage was initially performed but all required further operative procedures. We report a low incidence and mortality rate of necrotizing enterocolitis. Thrombocytopenia is confirmed as a marker of severity. Positive blood cultures for CoNS may explain, at least in part, the low mortality reported.

Necrotizing enterocolitis: recent scientific advances in pathophysiology and prevention

Necrotizing enterocolitis (NEC) is a leading cause of morbidity and mortality among infants in the neonatal intensive care unit. Here we review the epidemiology and pathophysiology of NEC, with an emphasis on the latest research findings and potential areas for future research. NEC continues to be one of the most devastating and unpredictable diseases affecting premature infants. Despite decades of research, the pathogenesis of this disease remains unclear, and prevention and treatment strategies are limited. Hopefully, future studies aimed at understanding premature intestinal defenses, commensal or probiotic bacterial influences, and possible genetic predisposition will lead to the improvement of prevention and treatment strategies.

Necrotising enterocolitis

Necrotising enterocolitis is one of the most common gastrointestinal emergencies in newborn infants. Here we review the epidemiology, clinical presentation, and pathophysiology of the disease, as well as strategies for diagnosis, management, and prevention. Necrotising enterocolitis is one of the most devastating and unpredictable diseases affecting premature infants. Despite decades of research, its pathogenesis remains unclear; diagnosis can be difficult; and treatment is challenging. We will need to improve our understanding of intestinal defences in premature infants, dietary and bacterial factors, and genetic effects that could predispose infants to necrotising enterocolitis before we can develop new strategies for prevention and treatment.

Epidemiology of necrotizing enterocolitis--Part II: Risks and susceptibility of premature infants during the surfactant era: a regional study

OBJECTIVES

We observed a reduced incidence of necrotizing enterocolitis (NEC) despite increased survival of extremely premature infants over the last two decades. A different susceptibility pattern to NEC according to gestation has been proposed. We aim to examine the influence of perinatal risk factors for NEC in infants less than 32 weeks gestation, in our region, in the post-surfactant era.

METHODS

NEC incidence, perinatal risk factors and neonatal outcomes were examined in a cohort of 4649 infants of 24-31 weeks gestation from the Neonatal Intensive Care Unit Study (NICUS) database, admitted during 1994-99.

RESULTS

A total of 178 (3.8%) infants developed NEC. More 24-27 weeks infants than 28-31 weeks infants had NEC (6.6% vs 2.6%, P < 0.001). Although low gestation infants had higher mortality and surgery need, post-operative survival (60%) was comparable to the higher gestation infants. NEC in the higher gestation group tended to be associated with perinatal risk factors, while risk factors were equally common in low gestation infants who developed NEC or not. Overall, gestation (P < 0.001), small for gestational age (P= 0.008), hyaline membrane disease (P < 0.001), placental abruption (P = 0.002) and earlier year of birth (P = 0.03) were independently associated with increased odds of NEC. Maternal hypertensive disease of pregnancy was associated with reduced NEC risk (P = 0.02).

CONCLUSIONS

The incidence of NEC continues to decrease in the surfactant era and the pattern of susceptibility to NEC is based on gestational age grouping and risk factors. The reduced risk associated with hypertensive disease of pregnancy is unexplained.

Resuscitation with 100% oxygen causes intestinal glutathione oxidation and reoxygenation injury in asphyxiated newborn piglets

OBJECTIVE

To compare mesenteric blood flow, oxidative stress, and mucosal injury in piglet small intestine during hypoxemia and reoxygenation with 21%, 50%, or 100% oxygen.

SUMMARY BACKGROUND DATA

Necrotizing enterocolitis is a disease whose pathogenesis likely involves hypoxia-reoxygenation and the generation of oxygen-free radicals, which are known to cause intestinal injury. Resuscitation of asphyxiated newborns with 100% oxygen has been shown to increase oxidative stress, as measured by the glutathione redox ratio, and thus may predispose to free radical-mediated tissue injury.

METHODS

Newborn piglets subjected to severe hypoxemia for 2 hours were resuscitated with 21%, 50%, or 100% oxygen while superior mesenteric artery (SMA) flow and hemodynamic parameters were continuously measured. Small intestinal tissue samples were analyzed for histologic injury and levels of oxidized and reduced glutathione.

RESULTS

SMA blood flow decreased to 34% and mesenteric oxygen delivery decreased to 9% in hypoxemic piglets compared with sham-operated controls. With reoxygenation, SMA blood flow increased to 177%, 157%, and 145% of baseline values in piglets resuscitated with 21%, 50%, and 100% oxygen, respectively. Mesenteric oxygen delivery increased to more than 150% of baseline values in piglets resuscitated with 50% or 100% oxygen, and this correlated significantly with the degree of oxidative stress, as measured by the oxidized-to-reduced glutathione ratio. Two of eight piglets resuscitated with 100% oxygen developed gross and microscopic evidence of pneumatosis intestinalis and severe mucosal injury, while all other piglets were grossly normal.

CONCLUSIONS

Resuscitation of hypoxemic newborn piglets with 100% oxygen is associated with an increase in oxygen delivery and oxidative stress, and may be associated with the development of small intestinal hypoxia-reoxygenation injury. Resuscitation of asphyxiated newborns with lower oxygen concentrations may help to decrease the risk of necrotizing enterocolitis.

Neonatal necrotizing enterocolitis: clinical considerations and pathogenetic concepts

Necrotizing enterocolitis (NEC), a disease affecting predominantly premature infants, is a leading cause of morbidity and mortality in neonatal intensive care units. Although several predisposing factors have been identified, such as prematurity, enteral feeding, and infection, its pathogenesis remains elusive. In the past 20 years, we have established several animal models of NEC in rats and found several endogenous mediators, especially platelet-activating factor (PAF), which may play a pivotal role in NEC. Injection of PAF induces intestinal necrosis, and PAF antagonists prevent the bowel injury induced by bacterial endotoxin, hypoxia, or challenge with tumor necrosis factor-a (TNF) plus endotoxin in adult rats. The same is true for lesions induced by hypoxia and enteral feeding in neonatal animals. Human patients with NEC show high levels of PAF and decreased plasma PAF-acetylhydrolase, the enzyme degrading PAF. The initial event in our experimental models of NEC is probably polymorphonuclear leukocyte (PMN) activation and adhesion to venules in the intestine, which initiates a local inflammatory reaction involving proinflammatory mediators including TNF, complement, prostaglandins, and leukotriene C4. Subsequent norepinephrine release and mesenteric vasoconstriction result in splanchnic ischemia and reperfusion. Bacterial products (e.g., endotoxin) enter the intestinal tissue during local mucosal barrier breakdown, and endotoxin synergizes with PAF to amplify the inflammation. Reactive oxygen species produced by the activated leukocytes and by intestinal epithelial xanthine oxidase may be the final pathway for tissue injury. Protective mechanisms include nitric oxide produced by the constitutive (mainly neuronal) nitric oxide synthase, and indigenous probiotics such as Bifidobacteria infantis. The former maintains intestinal perfusion and the integrity of the mucosal barrier, and the latter keep virulent bacteria in check. The development of tissue injury depends on the balance between injurious and protective mechanisms.

What every nurse needs to know about breast pumping: instructing and supporting mothers of premature infants in the NICU

Research has established that breast milk is the best source of nutrition for the premature infant. Because the infant is born prematurely, the mother will need support in expressing breast milk for her infant's use. The clinical nurse has the opportunity to educate the mother on the importance of breast milk for the premature infant and to support the mother through the course of pumping. However, many nurses are not sufficiently educated in the physiology of lactation to adequately support the mother. The purpose of this article is to educate the bedside nurse in the physiology of lactation so that the mother is adequately assisted in expressing breast milk for her vulnerable infant.

Nipple shields for preterm infants: effect on milk transfer and duration of breastfeeding

This study reports breastfeeding outcomes for 34 preterm infants whose mothers used ultrathin silicone nipple shields to increase milk transfer. Mean milk transfer was compared for 2 consecutive breastfeedings without and with the nipple shield. Total duration of breastfeeding was calculated for a maximum of 365 days. Mean milk transfer was significantly greater for feedings with the nipple shield (18.4 ml vs. 3.9 ml), with all 34 infants consuming more milk with the nipple shield in place. Mean duration of nipple shield use was 32.5 days, and mean duration of breastfeeding was 169.4 days; no association between these variables was noted. The nipple shield was used for 24.3% of the total breastfeeding experience, with no significant association between the percentage of time the shield was used and total duration of breastfeeding. These findings are the first to indicate that nipple shield use increases milk intake without decreasing total duration of breastfeeding for preterm infants.

Neonatal vascular catheters and their complications

There has been an evolution in vascular access in the neonate. Newer types of materials and catheters, such as PICC lines and ECMO catheters, are now available. The frequency of line placement has increased, and radiologists now perform many of these procedures. This places the radiologist in the position of not only diagnosing complications, but actually causing them. Knowledge of these complications can help the practitioner avoid them and diagnose them as quickly as possible when they occur.

Necrotizing enterocolitis: pathophysiology and prevention

Necrotizing enterocolitis (NEC) is the most common gastrointestinal emergency in the neonatal intensive care unit. It is a disease of medical progress in that more very low-birth-weight neonates are surviving than ever before and are thus susceptible to this potentially devastating disease. NEC received very little attention in the literature before the 1970s but now is well known to all neonatologists and pediatric surgeons. The 1500 to 2000 infants that die every year from this disease in the United States and the large number of infants who develop short gut syndrome from this disease only represent the tip of the iceberg of the problems NEC causes. The widespread fear of NEC among neonatologists and pediatric surgeons has contributed in large part to the use of the IV route rather than the gastrointestinal tract for nourishing these infants for relatively long periods. The consequences of this include a high incidence of sepsis, high hospital costs, and potential long-term neurodevelopmental disability because of poor nutrition during a very vulnerable period of growth and development. The purpose of this review is to provide a brief overview of the clinical presentation and current treatment for NEC, then provide a discussion of the pathophysiology on which strategies for prevention can be formulated.

Endotoxin and transient hypoxia cause severe acidosis in the piglet

PURPOSE

Both hypoxia and gram-negative sepsis are thought to play a role in the development of necrotizing enterocolitis (NEC). Endotoxin, a lipopolysaccharide (LPS), is a potent mediator of gram-negative sepsis. The author investigated the effect of LPS and hypoxia on arterial and mesenteric venous blood gas values in a piglet model.

METHODS

16 piglets (mean age, 9 days; mean weight, 3.2 kg) were anesthetized and mechanically ventilated. Catheters were placed in the aorta and the superior mesenteric vein (SMV). After a 30-minute stabilization period, piglets were randomly assigned to four experimental groups: normoxic ventilation (FIO2, 0.21), normoxic ventilation and LPS infusion (200 microg/kg, intravenously), hypoxic ventilation (FIO2, 0.10 for 20 minutes), or hypoxic ventilation and LPS infusion. All subjects were then monitored for an additional 30 minutes (recovery period). Multiple, paired blood gas samples were obtained from the aorta and SMV during the stabilization, experimental, and recovery periods.

RESULTS

Piglets subjected to both hypoxia and LPS experienced a much more severe acidosis in both the aorta (pH, 7.10 +/- 0.08) and SMV (pH, 7.03 +/- 0.09) than piglets subjected to either hypoxia or LPS alone (P < .05). In addition, LPS lowered the arterial oxygen saturation in piglets exposed to acute, transient hypoxia (36 +/- 4% v 59 +/- 12%, P < .05).

CONCLUSION

This study suggests that the combination of transient hypoxia and gram-negative sepsis may act synergistically to produce both a severe acidosis and decreased tissue oxygenation.

Necrotizing enterocolitis: the search for a unifying pathogenic theory leading to prevention

During the past two decades, necrotizing enterocolitis has emerged as a major cause of mortality and morbidity in premature infants. The specific cause of the disease remains enigmatic, but several putative risk factors provide clues to a pathophysiology that seems to be multifactorial. With the use of newly developed scientific tools, an understanding of the basic pathophysiologic cascade that causes necrotizing enterocolitis is emerging, providing hope for improved treatment and prevention.

Bacterial contaminated breast milk and necrotizing enterocolitis in preterm twins

A pair of preterm twins developed fatal necrotizing enterocolitis (NEC) in association with Staphylococcus epidermidis septicaemia after receiving contaminated expressed breast milk (EBM). S. epidermidis NEC can be associated with severe bowel inflammation, high morbidity and mortality. Breast milk is the most suitable nutrient for preterm infants but EBM should undergo regular screening for bacterial overgrowth. We urge caution before administering EBM found to be heavily contaminated with S. epidermidis to preterm infants.

[Necrotizing enterocolitis: symptomatology, diagnosis and therapeutic consequences]

Within a 6-year period ten patients with necrotizing enterocolitis (grade II-III; Bell) have been treated at the University Hospital, Göttingen. The following NEC incidences were calculated: birth weight < 1000 g: 2.4% (3/123); 1000-1500 g: 0.6% (2/308); 1501-2000 g: 0.7% (3/436); > 3000 g: approximately 0.006% (2/30,000 live births). In all patients onset of necrotizing enterocolitis (NEC) was associated with typical clinical symptoms such as abdominal distension, feeding problems, bloody stools. Only four out of ten patients had positive blood tests of various inflammatory parameters when diagnosed (C-reactive protein, neutrophil count, I/T-ratio). However, increased CRP levels were observed in all patients during the course of the disease (maximum levels: day 2-4 after diagnosis). During primarily conservative therapeutic management only one out of ten patients developed bowel perforation (day 6 after diagnosis) and immediate surgical treatment was carried out. In addition, in three patients who acquired strictures with obstruction of the colon, elective surgery was performed at a postnatal age of 51-77 days. All patients survived NEC without longterm sequelae. We conclude that a primarily conservative therapeutic regimen-whenever perforation and gangrene are absent-may be an alternative to early surgical intervention in NEC.

Epidemiology of necrotizing enterocolitis

The descriptive epidemiology of necrotizing enterocolitis (NEC) is presented. Areas addressed include incidence, race, sex, age of onset, mortality rates, and endemic versus epidemic disease. Both descriptive and case control studies are reviewed to uncover clues relevant to the causes, pathogenesis, and prevention of NEC.

Necrotizing enterocolitis. New thoughts about pathogenesis and potential treatments

Necrotizing enterocolitis (NEC) remains a major cause of morbidity and mortality in premature infants. An incomplete understanding of its pathogenesis has hampered efforts to devise an effective preventative strategy. New insights into the pathogenesis of NEC, particularly at the cellular and biochemical level, however, offer a rational basis for the development of new approaches to this disease.

Risk factors for necrotising enterocolitis: the influence of gestational age

Over a 7 year study period, 82 infants were identified who had necrotising enterocolitis (NEC). A case-control study of the 74 preterm infants was performed to determine those factors which contributed to the development of NEC. The 35 infants with NEC and gestation between 30-36 weeks, when compared with control infants matched for gestational age, had significantly lower birthweight centiles, cord pH, and 1 minute Apgar scores. By contrast, there were no significant differences between the 39 infants with NEC and controls in the 25-29 week group, except that fewer babies with NEC had received breast milk. The eight term babies all appeared to have an obvious predisposing event. We thus propose a model in which susceptibility to NEC is dependent on gestational age. In the 25-29 week range all babies are at risk on the basis of extreme prematurity. In the 30-36 week range asphyxiated and growth retarded babies are at increased risk, while at term a major predisposing event appears to be required.

Breast milk and neonatal necrotising enterocolitis

In a prospective multicentre study on 926 preterm infants formally assigned to their early diet, necrotising enterocolitis developed in 51 (5.5%). Mortality was 26% in stringently confirmed cases. In exclusively formula-fed babies confirmed disease was 6-10 times more common than in those fed breast milk alone and 3 times more common than in those who received formula plus breast milk. Pasteurised donor milk seemed to be as protective as raw maternal milk. Among babies born at more than 30 weeks' gestation confirmed necrotising enterocolitis was rare in those whose diet included breast milk; it was 20 times more common in those fed formula only. Other risk factors included very low gestational age, respiratory disease, umbilical artery catheterisation, and polycythaemia. In formula-fed but not breast-milk-fed infants, delayed enteral feeding was associated with a lower frequency of necrotising enterocolitis. With the fall in the use of breast milk in British neonatal units, exclusive formula feeding could account for an estimated 500 extra cases of necrotising enterocolitis each year. About 100 of these infants would die.