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 is common, its cause is unknown. NEC is the leading surgical emergency in neonates in North America.
Infectious complications associated with bowel necrosis include bacterial peritonitis, systemic sepsis, and intra-abdominal abscess formation.

Causes
NEC usually occurs in premature neonates (less than 34 weeks’ gestation) and those of low birth weight (less than 5 lb [2.3 kg]). NEC is occurring in more neonates, possibly because of the higher incidence and survival of premature and low-birth-weight neonates.

Possible risk factorsNEC can develop when the infant suffers perinatal hypoxemia due to shunting of blood from the gut to more vital organs. Subsequent mucosal ischemia provides an ideal medium for bacterial growth. Hypertonic formula may increase bacterial activity because—unlike maternal breast milk—it doesn’t provide protective immunity and because it contributes to the production of hydrogen gas. As the bowel swells and its integrity breaks down, gas-forming bacteria invade damaged areas, producing free air in the intestinal wall. This may result in fatal perforation and peritonitis.

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 gastric retention, is the earliest and most common sign of oncoming NEC, usually appearing from 1 to 10 days after birth.
• Other signs and symptoms include 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. They may develop as late as 3 months postoperatively.

Diagnosis
Successful treatment of NEC relies on early recognition based on the following diagnostic test results:
Abdominal X-rays confirm the diagnosis by showing nonspecific intestinal dilation and, in later stages of NEC, pneumatosis cystoides intestinalis (gas or air in the intestinal wall). Portal vein gas and fixed or thickened small bowel loops are also important radiographic findings. Sequential screening films are taken every 6 to 8 hours during the early disease stages.
Platelet count may show thrombocytopenia.
Serum sodium levels are decreased.
Arterial blood gas (ABG) levels show metabolic acidosis (a result of sepsis).
Bilirubin levels show infection-induced breakdown of red blood cells.
Blood and stool cultures identify the infecting organism.
Guaiac test detects occult blood in stools.

Treatment
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 a broad-spectrum antibiotic 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.