Necrotizing enterocolitis (NEC) is an acquired disease, primarily of preterm or sick neonates, characterized by mucosal or even deeper intestinal necrosis. It is the most common GI emergency among neonates. Symptoms and signs include feeding intolerance, lethargy, temperature instability, ileus, bloating, bilious emesis, hematochezia, reducing substances in the stool, apnea, and sometimes signs of sepsis. Diagnosis is clinical and is confirmed by imaging studies. Treatment is primarily supportive and includes nasogastric suction, parenteral fluids, TPN, antibiotics, isolation in cases of infection, and, often, surgery.
Over 85% of cases of NEC occur in premature infants. It occurs in about 1 to 8% of neonatal ICU admissions. Risk factors include prolonged rupture of the membranes with amnionitis, birth asphyxia, small-for-gestational-age infants, congenital heart disease, and exchange transfusions. The incidence may also be higher in infants fed hypertonic formulas.
In infants who develop NEC, 3 intestinal factors are usually present: a preceding ischemic insult, bacterial colonization, and intraluminal substrate (ie, enteral feedings).
The exact etiology is not clear. It is believed that an ischemic insult damages the intestinal lining, leading to increased intestinal permeability and leaving the intestine susceptible to bacterial invasion. NEC rarely occurs before enteral feedings and is less common among breastfed infants. However, once feedings are begun, ample substrate is present for proliferation of luminal bacteria, which can penetrate the damaged intestinal wall, producing hydrogen gas. The gas may collect within the intestinal wall (pneumatosis intestinalis) or enter the portal veins.
The initial ischemic insult may result from vasospasm of the mesenteric arteries, which can be caused by an anoxic insult triggering the primitive diving reflex that markedly diminishes intestinal blood flow. Intestinal ischemia may also result from low blood flow during an exchange transfusion, during sepsis, or from the use of hyperosmolar formulas. Similarly, congenital heart disease with reduced systemic blood flow or arterial O2 desaturation may lead to intestinal hypoxia/ischemia and predispose to NEC.
Necrosis begins in the mucosa and may progress to involve the full thickness of the intestinal wall, causing perforation with subsequent peritonitis and often free intra-abdominal air. Perforation occurs most commonly in the terminal ileum; the colon and the proximal small bowel are involved less frequently. Sepsis occurs in 33% of infants, and death may occur.
NEC may occur as clusters of cases or as outbreaks in neonatal ICUs. Some clusters appear to be associated with specific organisms (eg, Klebsiella,Escherichia coli, coagulase-negative staphylococci), but often no specific pathogen is identified.
Symptoms and Signs
Infants may present with feeding difficulties, bilious gastric residuals (after feedings) that may progress to bilious emesis, ileus manifested by abdominal distention, or gross or microscopic blood in stool. Sepsis may be manifested by lethargy, temperature instability, increased apneic spells, and metabolic acidosis.
Screening the stools of enterally fed premature infants for occult blood or reducing substances may help diagnose NEC early. Early x-rays may be nonspecific and reveal only ileus. However, a fixed, dilated intestinal loop that does not change on repeated x-rays indicates NEC. X-ray signs diagnostic of NEC are pneumatosis intestinalis and portal vein gas. Pneumoperitoneum indicates bowel perforation and an urgent need for surgery.
The mortality rate is 20 to 30%. Aggressive support and judicious timing of surgical intervention maximize the chance of survival.
Nonsurgical support is sufficient in over 75% of cases. Feedings must be stopped immediately if NEC is suspected, and the intestine should be decompressed with a double-lumen NGT attached to intermittent suction. Appropriate colloid and crystalloid parenteral fluids must be given to support circulation, because extensive intestinal inflammation and peritonitis may lead to considerable 3rd-space fluid loss. TPN is needed for 14 to 21 days while the intestine heals. Systemic antibiotics should be started at once with a β-lactam antibiotic (eg, ampicillin, ticarcillin) and an aminoglycoside. Additional anaerobic coverage (eg, clindamycin, metronidazole) may also be considered and should continue for 10 days (for dosage, see Table 1: Recommended Dosages of Selected Parenteral Antibiotics for Neonates). Because some outbreaks may be infectious, patient isolation should be considered, particularly if several cases occur within a short time.
The infant requires close monitoring; frequent complete reevaluation (eg, at least every 12 h); and serial abdominal x-rays, CBCs, platelet counts, and blood gases. Intestinal strictures are the most common long-term complication of NEC, occurring in 10 to 36% of infants who survive the initial event. Strictures typically manifest within 2 to 3 mo of an NEC episode. Strictures are most commonly noted in the colon, especially on the left side. Resection of the stricture is then required.
Surgical intervention is needed in < 25% of infants. Absolute indications are intestinal perforation (pneumoperitoneum), signs of peritonitis (absent intestinal sounds and diffuse guarding and tenderness or erythema and edema of the abdominal wall), or aspiration of purulent material from the peritoneal cavity by paracentesis. Surgery should be considered for an infant with NEC whose clinical and laboratory condition worsens despite nonsurgical support. During surgery, gangrenous bowel is resected, and ostomies are created. (Primary reanastomosis may be done if the remaining intestine shows no signs of ischemia.) With resolution of sepsis and peritonitis, intestinal continuity can be reestablished several weeks or months later.
Risk may be decreased by delaying feedings for several days to weeks in tiny or sick premature infants while providing TPN; feedings are slowly advanced over weeks. However, in some studies this approach was not beneficial. Breast milk seems to offer protection. For this and other reasons, breast milk should be encouraged for enteral feeding. Hypertonic formula, drugs, or contrast material should be avoided. Umbilical catheters, if required, should be placed below the renal arteries. Polycythemia should be treated promptly. Recent evidence suggests that probiotics (eg, Bifidus infantis, Lactobacillus acidophilus) may help prevent NEC, but further studies are required before they can be recommended routinely.
Last full review/revision November 2007 by William J. Cochran, MD
Content last modified February 2012