Necrotizing enterocolitis



Necrotizing enterocolitis (NEC) is a medical condition primarily seen in premature infants, where portions of the bowel undergo necrosis (tissue death).

Signs and symptoms
The condition is typically seen in premature infants, and the timing of its onset is generally inversely proportional to the gestational age of the baby at birth, i.e. the earlier a baby is born, the later signs of NEC are typically seen. Initial symptoms include feeding intolerance, increased gastric residuals, abdominal distension and bloody stools. Symptoms may progress rapidly to abdominal discoloration with intestinal perforation and peritonitis and systemic hypotension requiring intensive medical support.

Diagnosis
The diagnosis is usually suspected clinically but often requires the aid of diagnostic imaging modalities. Radiographic signs of NEC include dilated bowel loops, paucity of gas, a "fixed loop" (unaltered gas-filled loop of bowel), pneumatosis intestinalis, portal venous gas, and pneumoperitoneum (extraluminal or "free air" outside the bowel within the abdomen). The pathognomic finding on plain films is pneumatosis intestinalis. More recently ultrasonography has proven to be useful as it may detect signs and complications of NEC before they are evident on radiographs. Diagnosis is ultimately made in 5–10% of very low-birth-weight infants (<1,500g). However, it is not known whether some underlying pathology contributes to premature birth and low birth weight.

The clinical features are divided into 3 stages:

Stage 1 — Apnea, bradycardia, lethargy, abdominal distension and vomiting.

Stage 2 — Pneumatosis intestinalis and the above features.

Stage 3 — Low blood pressure, bradycardia, acidosis, disseminated intravascular coagulation (DIC) and anuria.

Treatment
Treatment consists primarily of supportive care including providing bowel rest by stopping enteral feeds, gastric decompression with intermittent suction, fluid repletion to correct electrolyte abnormalities and third space losses, support for blood pressure, parenteral nutrition, and prompt antibiotic therapy. Monitoring is clinical, although serial supine and left lateral decubitus abdominal roentgenograms should be performed every 6 hours. Where the disease is not halted through medical treatment alone, or when the bowel perforates, immediate emergency surgery to resect the dead bowel is generally required, although abdominal drains may be placed in very unstable infants as a temporizing measure. Surgery may require a colostomy, which may be able to be reversed at a later time. Some children may suffer later as a result of short bowel syndrome if extensive portions of the bowel had to be removed.

Cause
NEC has no definitive known cause. An infectious agent has been suspected, as cluster outbreaks in neonatal intensive care units (NICUs) have been seen, but no common organism has been identified. Pseudomonas aeruginosa is suspected for causing necrotising enterocolitis in premature infants and neutropaenic cancer patients, often secondary to gut colonisation. A combination of intestinal flora, inherent weakness in the neonatal immune system, empirical antibiotic use for 5 days or more, alterations in mesenteric blood flow and milk feeding may be factors. The most common area of the bowel affected by NEC is near the ileocecal valve (the site of transition between the small and large bowel). NEC is almost never seen in infants before oral feedings are initiated. Formula feeding increases the risk of NEC by tenfold compared to infants who are fed breastmilk alone. Expressed breast milk protects the premature infant not only by its antiinfective effect and its immunoglobulin agents but also from its rapid digestion.

A study by the Neonatal Research Network, published in the journal Pediatrics in January 2009, conducted a study regarding the administration of empirical antibiotics in extremely low birth weight infants. The research demonstrated that empirical antibiotic therapy over 5 days for extremely low birth weight babies increased the chance of necrotizing enterecolitis by 4% for each additional day over 5 days.

Prevention
Once a child is born prematurely, thought must be given to decreasing the risk for developing NEC. Toward that aim, the methods of providing hyperalimentation and oral feeds are both important. A recent study, by researchers in Peoria, IL, published in Pediatrics in 2008, demonstrated that using a higher rate of lipid (fats and/or oils) infusion for very low birth weight infants in the first week of life resulted in zero infants developing NEC in the experimental group, compared with 14% with NEC in the control group (They started the experimental group at 2 g/kg/d of 20% IVFE and increased within two days to 3 g/kg/d; Amino acids were started at 3 g/kg/d and increased to 3.5).

Neonatologists at the University of Iowa NICU reported on the importance of providing small amounts of trophic oral feeds of human milk starting ASAP, while the infant is being primarily fed intravenously, in order to prime the immature gut to mature and become ready to receive greater oral intake. Human milk from a milk bank or donor can be used if mother's milk is unavailable. The gut mucosal cells do not get enough nourishment from arterial blood supply to stay healthy, especially in very premature infants, where the blood supply is limited due to immature development of the capillaries, so nutrients from the lumen of the gut are needed.

Prognosis
Typical recovery from NEC if medical, non-surgical treatment succeeds, includes 10–14 days or more without oral intake and then demonstrated ability to resume feedings and gain weight. Recovery from NEC alone may be compromised by co-morbid conditions that frequently accompany prematurity. Longterm complications of medical NEC include bowel obstruction and anemia.

Despite a significant mortality risk, long-term prognosis for infants undergoing NEC surgery is improving, with survival rates of 70–80%. "Surgical NEC" survivors are at-risk for complications including short bowel syndrome, and neurodevelopmental disability.