Necrotizing Enterocolitis

Neonatal necrotizing enterocolitis (NEC) is a clinical condition characterized by an initial mucosal intestinal injury that may progress to transmural bowel necrosis. Although NEC occurs frequently, its cause is unknown. NEC is the leading surgical emergency in neonates in North America.

NEC typically occurs within the first 2 weeks of life, usually after milk feeding has begun (at first, feedings are usually given through a tube that goes directly to the baby's stomach). About 10% of babies weighing less than 1,500 grams (3 lbs., 5 oz.) experience NEC. These premature infants have immature bowels, which are sensitive to changes in blood flow and prone to infection. They may have difficulty with blood and oxygen circulation and digestion, which increases their chances of developing NEC.

With early detection, the survival rate is 60% to 80%. Infectious complications associated with bowel necrosis include bacterial peritonitis, systemic sepsis, and intraabdominal abscess formation.

Causes

It is not clear exactly what causes NEC. It is thought that the intestinal tissues are somehow weakened by too little oxygen or blood flow. When feedings are started and the food moves into the weakened area of the intestinal tract, bacteria from the food can damage the intestinal tissues. The tissues may be severely damaged and die, which can cause a hole to develop in the intestine. This can lead to severe infection in the abdomen.

Signs and symptoms

Any infant who has suffered from perinatal hypoxemia has the potential for developing NEC. A distended (especially tense or rigid) abdomen, with gasrile retention, is the earliest and most common sign of oncoming NEC, usually appearing from 1 to 10 days after birth.

Other clinical features are increasing residual gastric contents (which may contain bile), bilious vomitus, and occult or gross blood in stools. One-fourth of patients have bloody diarrhea. A red or shiny, taut abdomen may indicate peritonitis

Nonspecific signs and symptoms include thermal instability, lethargy, metabolic acidosis, jaundice, and disseminated intravascular coagulation (DIC).

The major complication is perforation, which requires surgery.

Recurrence of NEC and mechanical and functional abnormalities of the intestine, especially stricture, are the usual cause of residual intestinal malfunction in any infant who survives acute NEC and may develop as late as 3 months postoperatively.

Diagnosis

The diagnosis of NEC is usually confirmed by the presence of an abnormal gas pattern seen on an X-ray. This is determined by a "bubbly" appearance of gas in the walls of the intestine, large veins of the liver, or the presence of air outside of the intestines in the abdominal cavity. A surgeon may insert a needle into the abdominal cavity to withdraw fluid to determine whether there is a hole in the intestines.

Treatment

Up to 90% of infants with NEC can be managed without surgery. The first signs of NEC necessitate discontinuation of oral intake to rest the injured bowel. I. V. fluids, including total parenteral nutrition, maintain fluid and electrolyte balance and nutrition during this time; passage of a nasogastric (NG) tube allows bowel decompression.

Correction of hypoxemia, hypotension, acidosis, and any other reversible medical problems is needed. Optimizing cardiac performance is necessary. Serial physical examinations, platelet counts, lactate levels, and ABG levels are the most useful indications of progressive sepsis.

Antibiotic therapy

Drug therapy consists of parenteral administration of broad-spectrum antibiotics to suppress bacterial flora and prevent bowel perforation. (These drugs can also be administered through an NG tube if necessary.)

Surgery

Surgery is indicated if the patient shows any of the following signs or symptoms: signs of perforation (free intraperitoneal air on X-ray) or symptoms of peritonitis, respiratory insufficiency (caused by severe abdominal distention), progressive and intractable acidosis, or DIC. Surgery removes all necrotic and acutely inflamed bowel and creates a temporary colostomy or ileostomy.

Prevention

In very small or sick premature infants, the risk for necrotizing enterocolitis may be diminished by beginning parenteral nutrition and delaying enteral feedings for several days to weeks.

Some have suggested that breast milk provides substances that may be protective, but there is no evidence that this reduces the risk of infection. A large multicenter trial showed that steroid drugs given to women in preterm labor may protect their offspring from necrotizing enterocolitis.

Sometimes necrotizing enterocolitis occurs in clusters, or outbreaks, in hospital newborn (neonatal) units. Because there is an infectious element to the disorder, infants with necrotizing enterocolitis may be isolated to avoid infecting other infants. Persons caring for these infants must also employ strict measures to prevent spreading the infection.