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What is Necrotizing enterocolitis and explain in detail?
Necrotizing enterocolitis (NEC) is a devastating intestinal disease that affects premature or very low birth weight infants. Symptoms may include poor feeding, bloating, decreased activity, blood in the stool, vomiting of bile, bowel death, multiorgan failure, and even death.The exact cause is unclear. However, several risk factors have been identified. Consistently described risk factors include formula feeding, intestinal dysbiosis, low birth weight, and prematurity. Maternal factors such as chorioamnionitis, cocaine abuse, in utero growth restriction, intrahepatic cholestasis during pregnancy, increased body mass index, lack of prenatal steroids, mode of delivery, placental abruption, preeclampsia, and smoking have not been consistently implicated with the development of NEC. Other risk factors potentially implicated include congenital heart disease, birth asphyxia, exchange transfusion, and prelabor rupture of membranes. The underlying mechanism is believed to involve a combination of poor blood flow and infection of the intestines. Diagnosis is based on symptoms and confirmed with medical imaging.Prevention includes the use of breast milk and probiotics. Treatment includes bowel rest, orogastric tube, intravenous fluids, and intravenous antibiotics. Surgery is required in those who have free air in the abdomen. A number of other supportive measures may also be required. Complications may include short-gut syndrome, intestinal strictures, or developmental delay.About 7% of those who are born prematurely develop NEC; however the odds of an infant developing this illness is directly related to the intensive care unit they are placed in. Onset is typically in the first four weeks of life. Among those affected, about 25% die. The sexes are affected with equal frequency. The condition was first described between 1888 and 1891.

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 and failure to thrive, 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.

Cause
The exact cause is unclear. Several risk factors have been implicated:

Maternal factors
Acid-suppressing medications
Chorioamnionitis
Cocaine abuse
In utero growth restriction
Increased body mass index
Intrahepatic cholestasis during pregnancy
Lack of prenatal steroids
Mode of delivery
Placental abruption
Pre-eclampsia
Smoking

Main risk factors
Low birth weight
Prematurity
Formula feeding (bovine based)
Intestinal dysbiosis

Other risk factors
Acute hypoxia
Antibiotic exposure
Blood transfusions
Cardiac anomalies
Neonatal anemia
Poor intestinal perfusion
Prolonged use of indomethacin for patent  ductus arteriosus closure

Diagnosis
Diagnosis is usually suspected clinically, but often requires the aid of diagnostic imaging, most commonly radiography, which can show the intestines and may show areas with death tissue or a bowel perforation. Specific radiographic signs of NEC are associated with specific Bells stages of the disease:
Bells stage 1 (suspected disease):
Mild systemic disease (apnea, lethargy, slowed heart rate, temperature instability)
Mild intestinal signs (abdominal distention, increased gastric residuals, bloody stools)
Nonspecific or normal radiological signs
Bells stage 2 (definite disease):
Mild to moderate systemic signs
Additional intestinal signs (absent bowel sounds, abdominal tenderness)
Specific radiologic signs (pneumatosis intestinalis or portal venous gas)
Laboratory changes (metabolic acidosis, too few platelets in the bloodstream)
Bells stage 3 (advanced disease):
Severe systemic illness (low blood pressure)
Additional intestinal signs (striking abdominal distention, peritonitis)
Severe radiologic signs (pneumoperitoneum)
Additional laboratory changes (metabolic and respiratory acidosis, disseminated intravascular coagulation)Ultrasonography has proven to be useful, as it may detect signs and complications of NEC before they are evident on radiographs, specifically in cases that involve a paucity of bowel gas, a gasless abdomen, or a sentinel loop. Diagnosis is ultimately made in 5–10% of very-low-birth-weight infants (<1,500g).

		
Diagnosis of NEC is more challenging in premature infants, due to inexplicit symptoms and radiographic signs. The most preterm infant is at highest risk of developing NEC.

Prevention
Prevention includes the use of breast milk and probiotics. A 2012 policy by the American Academy of Pediatrics recommended feeding preterm infants human milk, finding "significant short- and long-term beneficial effects," including reducing the rate of NEC by a factor of one-half to three-quarters.Small amounts of oral feeds of human milk starting as soon as possible, while the infant is being primarily fed intravenously, primes the immature gut to mature and become ready to receive greater intake by mouth. Human milk from a milk bank or donor can be used if mothers 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.Towards understanding intervention with human milk, experts have noted cows and human milk differ in their immunoglobular and glycan compositions. Due to their relative ease of production, human milk oligosaccharides (HMO) are a subject of particular interest in supplementation and intervention.A Cochrane review in 2020 found low- to moderate-quality evidence that supplementation of probiotics enterally "prevents severe NEC, as well as all-cause mortality in preterm infants" and that further high-quality trials are needed to inform policy and practice.Advancing enteral feed volumes at lower rates does not appear to reduce the risk of NEC or death in very preterm infants and seems to increase the risk of invasive infection.  Not beginning feeding an infant by mouth for more than 4 days does not appear to have protective benefits.

Treatment
If a baby is diagnosed with NEC, treatment should begin immediately. 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 X-rays should be performed every six hours.As an infant recovers from NEC, feeds are gradually introduced. "Trophic feeds" or low-volume feeds (<20 ml/kg/day) are usually initiated first. How and what to feed are determined by the extent of bowel involved, the need for surgical intervention, and the infants clinical appearance.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