Necrotizing Enterocolitis

The exact etiology of necrotizing enterocolitis is not clear. However, the increased permeability and immature immune function of the immature intestinal tract are predisposing factors. 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 have begun 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. Dysbiosis (alteration of the intestinal microbiome), such as that which occurs after treatment with antibiotics or acid-suppressing drugs, may also be a contributing factor because it increases potentially pathogenic bacteria.

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 oxygen desaturation may lead to intestinal hypoxia/ischemia and predispose to NEC.

NEC may occur as clusters of cases or as outbreaks in neonatal intensive care units. Some clusters appear to be associated with specific organisms (eg, Klebsiella, Escherichia coli, coagulase-negative staphylococci, Pseudomonas, Clostridioides difficile), but often no specific pathogen is identified.

Infants may present with feeding difficulties and bloody or bilious gastric residuals (after feedings) that may progress to bilious emesis, ileus manifested by abdominal distention, or gross blood in stool. Sepsis may be manifested by lethargy, temperature instability, increased apneic spells, and metabolic acidosis.

Early x-rays may be nonspecific and reveal only ileus. However, a fixed, dilated intestinal loop (sentinel loop) that does not change on repeated x-rays is very concerning for NEC. X-ray signs diagnostic of NEC are pneumatosis intestinalis and portal vein gas. Pneumoperitoneum Pneumoperitoneum Pulmonary air-leak syndromes involve dissection of air out of the normal pulmonary airspaces. (See also Overview of Perinatal Respiratory Disorders.) Extensive physiologic changes accompany... read more indicates bowel perforation and an urgent need for surgery.

Ultrasonography is being used increasingly in cases of NEC. With ultrasonography, clinicians have the ability to look at bowel wall thickness, pneumatosis intestinalis, and blood flow. This technique, however, is very operator dependent, and plain x-rays are still more commonly used.

The mortality rate is 20 to 30%. Aggressive support and judicious timing of surgical intervention maximize the chance of survival.

At-risk infants Risk factors Necrotizing enterocolitis is an acquired disease, primarily of preterm or sick neonates, characterized by mucosal or even deeper intestinal necrosis. It is the most common gastrointestinal emergency... read more should ideally be fed breast milk, and feedings should begin with small amounts that are gradually increased according to standardized protocols. (Preterm formula is an appropriate substitute if breast milk is not available.) Hypertonic formula, drugs, or contrast material should be avoided. Anemia, low oxygen saturations, and polycythemia Perinatal Polycythemia and Hyperviscosity Syndrome Polycythemia is an abnormal increase in red blood cell mass, defined in neonates as a venous hematocrit ≥ 65%; this increase can lead to hyperviscosity with sludging of blood within vessels... read more should be treated promptly. When possible, antibiotics and acid-supressing drugs should be avoided.

Probiotics (eg, Bifidus infantis, Lactobacillus acidophilus) help prevent NEC, but further studies to determine optimal dosing and appropriate strains are required before routine use (1 Prevention references Necrotizing enterocolitis is an acquired disease, primarily of preterm or sick neonates, characterized by mucosal or even deeper intestinal necrosis. It is the most common gastrointestinal emergency... read more ).

Corticosteroids may be given to pregnant women who are at risk of preterm birth to help prevent necrotizing enterocolitis (2 Prevention references Necrotizing enterocolitis is an acquired disease, primarily of preterm or sick neonates, characterized by mucosal or even deeper intestinal necrosis. It is the most common gastrointestinal emergency... read more ).