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Necrotizing Enterocolitis (NEC)

How often does NEC occur?

Necrotizing enterocolitis (NEC) occurs in approximately 25,000 babies per year. Despite modern medicine infants with the most serious form still have a one in four chance of dying. NEC is the most serious and frequent stomach and intestinal (gastrointestinal, GI) problem of low-birth-weight infants. The result of dramatic improvements in the management of the lung and nutritional needs of premature infants has improved the immediate survival of the infants so now they are living longer and, thus, have a greater chance of developing NEC.

For infants weighing less than about 3 pounds (1500 grams), the chance of developing NEC increases to approximately 1 in 18 and accounts for 1/7th of all deaths occurring after 1 week of life. The major cause for these deaths is overwhelming infection that the infants cannot fight off.

Why does NEC occur?

Despite extensive study, the cause of NEC is uncertain. There are likely to be many causes, but a lack of blood flow to the intestine and infection are probably critical to the development of NEC. Low blood pressure, decreased blood volume, or decreased oxygen in the blood at birth, have been suggested as possible causes.

More recent studies indicate that there are overall two important factors in the development of NEC: (1) decreased blood flow to the intestine caused by something, probably bacteria, and (2) a vulnerable patient, which most often is a premature infant.

The following is a concept of how NEC might occur. Newborn premature infants are vulnerable to developing NEC because the intestine has a decreased defense against invasion by bacteria. Lack of breast-feeding results in the absence important breast milk components. The immature intestinal cells function poorly and may receive inadequate nutrients to maintain what little function they do have. Stomach, pancreatic, and intestinal secretions are diminished. In addition, premature infants are born with an inadequate immune system, thus they cannot fight off infection.

The infant is admitted to a neonatal intensive care unit usually for treatment of lung failure and is exposed to unusual, strong “intensive care” bacteria. Antibiotics frequently are administered which alters the patient’s normal intestinal bacteria, and formula feeding provides nutrition for the bacteria that are present in the intestine. The intestine doesn’t work well so that the contents in the intestine aren’t pushed along. This permits these bacteria to grow and set up residence in the intestine.

Depending on the number and strength of the bacteria and the presence or absence of intestinal damage from decreased blood supply to the intestine, bacteria may get through the inner lining of the intestine. Because of the decreased defense systems, bacterial killing is not effective when the bacteria enter the body tissues. With time the damage to the intestine worsens until the intestine dies and perforates (ruptures).

What does NEC look like?

The most common area where NEC occurs is the last part of the small intestine followed by the colon (large intestine). Together the large and small intestines are involved in 44% of these patients. The disease can involve a single (50%) or multiple portions of the intestine. In the most severe form of NEC at least 75% of the intestine dies. When this occurs almost all of the patients die.

The intestine in NEC shows patchy areas of bleeding into the wall of the intestine with gas inside the intestinal wall (Figure 1). However, some areas have a normal appearance. Other, areas of the bowel may be obviously dead. The inside lining may have multiple ulcers with wide areas of damage.

When the intestine with NEC is examined under a microscope, there is a patchy loss of the inner lining (89%). There is swelling and blood in the intestinal middle layer. Eventually the cells die and the inner layer develops ulcers. Air in the intestinal wall occurs as a result of gas-forming bacteria entering the intestinal wall. Despite the presence of bacteria in the bowel wall, the body’s reaction is minimal early and becomes more evident later during healing. Healing may lead to stricture formation (narrowing of the intestine) in 5% to 10% of patients who recover from the initial NEC episode. This usually shows up 2-6 weeks after the initial NEC event.

What is seen in NEC?

A distended abdomen is almost always seen and is the most common finding. The abdomen is usually soft, but as the disease progresses it may become firm and tender (painful to the touch). One may be able to feel enlarged intestines and air within the intestine or under the abdominal wall. Swelling and a red or blue color of the abdominal wall are seen in approximately 5% of patients as a reaction to the underlying sick intestine. A mass of intestines occasionally can be felt. Green (bilious) vomiting occurs in three fourths of these infants.

Diarrhea occurs in 20% of patients early on. Blood in the stool is common, although massive bleeding is rare. One may also see lethargy (acting sleepy and not moving), inability to keep the temperature normal, sudden stops in breathing and need for oxygen and the breathing machine (ventilator), and decreased heart rate; shock (decreased blood pressure) may be the outcome.

Laboratory Findings

The white blood cell count can be high or low. A low white blood cell count indicates a more severe infection and a poorer outcome.

Decreased platelet count is the result of platelets being consumed by a poisonous substance produced by bacteria. Greater than 80% of patients have platelet counts which are very low (less than 100,000/mm 3). Increased acid in the blood stream (metabolic acidosis) occurs in 70% to 90% of patients and is the result of decreased blood flow to the intestine and serves to worsen the entire status of the patient. Examination of the stool for blood is helpful because rectal bleeding is seen frequently. None of the laboratory tests can absolutely say that NEC is present. A decreasing platelet count is probably the most helpful indication of worsening NEC.

What is seen with x-rays and other radiology tests?

X-ray findings have served as the cornerstone of diagnosis for NEC. X-rays of the abdomen and chest are taken. The findings most commonly associated with NEC are pneumatosis intestinalis (air in the intestinal wall), portal vein gas (air in the vein going from the intestine to the liver), pneumoperitoneum (air inside the abdomen, but outside the intestine), fluid inside the abdomen, and persistently enlarged (dilated) intestinal loops.

Pneumatosis Intestinalis

Intestinal wall gas is the most common diagnostic sign of NEC, occurring in 98% of patients. This sign may come and go and commonly is an early rather than a late finding. It is seen more frequently in infants who have been fed compared with unfed infants but eventually is seen in all patients. In patients with the most severe form of NEC extensive pneumatosis involving large portions of the small and large intestine is seen (Figure 2).

Portal Vein Gas

Gas gets into the liver in the following manner: gas in the intestine wall is absorbed into the intestinal venous system and travels into the portal vein where it is trapped in the small branches of he portal vein inside the liver (Figure 3). The presence of gas in the portal venous system comes and goes which accounts for the fact that it is not often seen. In cases of severe NEC, portal vein air is present in 60% of patients.

Pneumoperitoneum

Free air in the abdominal cavity is a result of perforation (rupture) of the intestine. This can be seen in 10% to 20% of patients with NEC. Intestinal perforation seen at the time of an operation was accompanied by free air on the x-ray in only two thirds of the patients, suggesting that perforation can occur without free air being seen on the x-ray.

Ascites (fluid in the abdomen)

The x-ray finding of free fluid in the abdominal cavity, seen in 10% of patients, consists of a distended abdomen with gas-filled loops of intestine in the center of the abdomen surrounded by a white haziness within the abdomen. The white haziness is the fluid (ascites) in the abdomen. The combination of ascites and portal vein gas has been associated with a high death rate. A fourth of patients with surgically proven intestinal perforation have ascites, but 15% of patients with proven intestinal perforation have neither ascites nor free air on x-rays of the abdomen.

Fixed Loop Sign

The finding of a single loop or several loops of dilated (enlarged) small intestine that remain unchanged in position for 24 to 36 hours is referred to as the persistent loop sign and suggests lack of movement of the intestine due to death of a segment of intestine.

X-ray Studies With Dye (contrast)

Dye (contrast) studies of the gastrointestinal tract for NEC are performed infrequently because of risk of obstruction (blockage) and perforation (rupture) with such studies. Under certain circumstances, they may help, however, to diagnose NEC in premature infants and to differentiate NEC from other diseases. Early diagnosis of NEC and prompt treatment may decrease the complications and death rate.

When contrast studies are performed: findings strongly suggestive of NEC include ulcers in the intestinal lining, spasm and a thickened bowel wall, narrowing of the intestine, and air in the bowel wall. Tiny amounts of contrast outside of the intestine suggest that tiny areas of perforation are present. These findings may identify patients with NEC in whom the diagnosis has been in question. Contrast studies are rarely indicated except in the later phase of NEC when narrowing (stricture) or blockage (obstruction) of the intestine is a potential problem.

Ultrasound

Although x-rays are usually all that is required for diagnosis, ultrasound has been used in some cases. One of the main ultrasound signs is portal venous gas, which shows up as bright white spots or lines within the liver. Occasionally, air in the wall of the intestine can be identified by ultrasound. The most helpful information from ultrasound is identifying free fluid in the abdomen.

What are the stages of NEC?

A NEC classification was introduced by Bell and colleagues as follows: stage I, infants who have findings suggestive of NEC; stage II, infants who definitely have NEC; and stage III, infants who are in the advanced stages of NEC with evidence of intestinal death. However, the clinical findings rather than the stage determines how the patient is treated.

How is NEC treated?

Nonoperative Treatment

Unless there is evidence of intestinal death or perforation (rupture of the intestines), the initial treatment of NEC is without an operation. It is essential to decrease the amount of gas in the stomach and intestines (GI tract) by placing a tube through the mouth or nose into the stomach and applying suction to the tube. A normal blood pressure must be maintained to continue to have blood flow to the intestine in order to diminish the risk of further intestinal damage.

In addition to giving fluid into the veins through an intravenous line (IV), the electrolytes and pH (normal chemicals in the blood) should be maintained at normal levels. Intravenous nutrition should be initiated as soon as it is practical to do so. The most important part of care is antibiotic therapy.

The antibiotic used vary according to the typical bacteria in each hospital, but a combination of three antibiotics among ampicillin, gentamicin, Flagyl, clindamycin, and vancomycin have been the most common because of the typical bacteria involved. In some intensive care units, cefotaxime is used with vancomycin. Other antibiotic combinations may be needed, especially when fungal (yeast) is a problem.

The course of NEC is monitored by physical examination, x-rays of the abdomen, platelet and white blood cell counts, and the amount of oxygen, carbon dioxide, and acid (pH) in the blood. Antibiotics are continued often for of 10-14 days in severe cases. The tube which is applying suction to the GI tract is continued until there is evidence of complete recovery of intestinal function which is often after 10-14 days. If there are no ongoing signs of NEC, small quantities of dilute formula are administered, but in severe cases this may be after 10-14 days of resting the intestine. Feedings are advanced as long as they are tolerated.

Indications for Operation

The optimal time for an operation is just at the time of intestinal death or perforation. The best indication for operation is air in the abdominal cavity, which suggests that bowel perforation has occurred. Other reasons for an operation include that the patient is getting worse despite aggressive nonoperative management, persistent acid production (low pH), continuing drop in platelet count despite platelet transfusions, discoloration of the abdomen, presence of a mass in the abdomen, a fixed enlarged (dilated) loop of intestine, fluid in the abdomen, and portal vein gas. None of these findings by themselves indicate that dead or perforated bowel is present. Probably the best sign of dead intestine is continuing low platelet count despite platelet transfusions.

Pneumoperitoneum (free air in the abdomen outside of the intestines)

Infants who have NEC and air in the abdominal cavity in general require an operation, especially if they are getting sicker (Figure 4). Not all patients who have perforation (rupture) of the intestines have air in the abdomen. The decision to proceed with an operation is often one of clinical judgment.

Fixed Intestinal Loop

The finding of a fixed loop of dilated intestine for more than 24 hours is uncommon but strongly suggests intestinal death. It is not universally accurate and an estimate of intestinal death when a fixed loop is seen is approximately 60%.

Ascites (fluid in the abdomen)

If there are x-ray signs of abdominal fluid (see earlier) or fluid is confirmed by ultrasound, 20% to 40% of patients have a dead intestine. If fluid is present, paracentesis (sampling of the fluid with a needle) may be performed and the fluid examined for signs of infection. If bacteria are found in the fluid or if the fluid is green or brown in color, then intestinal perforation is likely.

Portal Vein Gas

Several reports have indicated that the finding of portal venous gas may be a reason to do an operation. Since 85% of patients with portal vein gas require an operation with all of those having dead intestine at the time of the operation.

Operative Management

Under optimal circumstances, the premature infant’s condition should be stabilized with IV fluids given to establish normal vital signs and good urine output. In reality, this may not be possible. Transfusions of blood and platelets are given as needed. If the ability to clot blood is decreased, it must be corrected. In the operating room, heat loss from the newborn must be minimized. During surgery, the bowel is kept inside the abdomen as much as possible to decrease loss of heat and fluid from the surface of the intestines.

The incision is usually across the abdomen just above the belly button. Only perforated or dead intestine is removed and as much bowel as possible is saved. Every effort is made to preserve the junction of the small and large intestine (the ileocecal valve). The upstream end is most often brought through the wall of the abdomen as a “stoma” or “ostomy.” The intestinal contents will then temporarily empty into a bag.

Approximately 20% of patients taken to surgery have the very severe form of NEC. In this instance the surgeon may encounter a situation where only a small portion of the first part of the small intestine is alive along with the last part of the large intestine. Everything in between is dead. At this point, many surgeons decide to close the abdomen and stop further treatment.

Many of these patients are critically ill and will not survive even if treatment is continued. In rare instances, creating an upstream stoma and removing all of the dead intestine has led to survival, but the patient will require a small bowel transplant, which currently has many problems, complications, and a questionable quality of life. If the patient remains stable and it is believed that there is a sufficient amount of small intestine ultimately to allow adequate food intake, the patient is maintained on total intravenous nutrition (TPN, food delivered into the blood stream).

There is no universal agreement on when to close a stoma. If there is sufficient intestinal length and the feedings are tolerated with adequate weight gain, most surgeons delay closure for a minimum of 2 months. The patient may be even sent home for a time.

Some patients, however, tolerate feedings poorly, even though they have sufficient intestinal length. Because of failure to grow or ongoing salt and water loss, some patients may require earlier stoma closure. Stomal dysfunction from narrowing is common. If this occurs and the infant is more than 4 weeks postoperative, many surgeons close the stoma rather than redoing it. Infants with insufficient bowel to maintain adequate nutrition orally can be maintained on TPN. Patients should have the stoma closed as soon as possible if they develop repeated central line infections or liver disease from the TPN.

When the dead intestine is just in one small area and the remaining intestine appears undamaged, some surgeons have had success with removal of that small portion of the intestine with sewing the two ends together immediately. This approach avoids the complications from and need for a stoma and a second operation. However, it should only be done if the area of dead intestine is small; the surrounding intestine is healthy; and the patient’s general condition is good.

The use of a drain placed into the abdomen under local anesthesia can be done to treat extremely ill and premature infants with perforated intestine. Two thirds of the newborns with intestinal perforation who are treated with a drain will survive. It is currently thought that placing a drain may effectively treat the infection due to both the NEC and the intestine perforation while avoiding the effects of a big operation on such small, severely ill newborns. A study to evaluate whether placing a drain or doing the full operation is the better approach is underway.

Intestinal Strictures

Strictures (narrowing) result from healing of an area of severe injury to the intestine (Figure 5). Between 11% and 35% of patients with NEC develop strictures. The most common site for narrowing is the large intestine (70%) followed by the last part of the small intestine (15%).

Of colonic (large intestine) strictures, 60% involve the left side of the colon and the most common site is that portion of the colon, which exists in the left upper area of the abdomen (21%). Most patients have just one stricture, but multiple strictures may occur. Colonic strictures are typically without symptoms in patients who have had a small intestine stoma formed because no fluid or air is permitted to build up at the stricture.

Because of the danger of closing a stoma in the presence of a blockage, it is important to perform a dye study of the colon and downstream intestine before stoma closure. If a stricture is found, it can be removed during the procedure to close the stoma. Of the patients treated nonoperatively, slightly more than half with colonic strictures are symptomatic and present with intestinal blockage. Current consensus is that patients treated nonoperatively who develop delayed signs of partial intestinal blockage should have dye (contrast) x-ray studies to evaluate for a stricture. If one is found, removal with immediate connection of the two ends of the intestine is performed.

What is the survival of newborns with NEC?

There has been a steady improvement in the survival of patients with NEC. The increased survival has been most noticeable in infants weighing less than 1000 grams (about 2 pounds) with gestational age (time inside the mother) less than 28 weeks. The improved survival in this group has been attributed to earlier diagnosis and more effective treatment. The progress made in the management of low-birth-weight, critically ill infants also has contributed to this increased rate of survival from NEC. Presently the survival in extremely premature infants who require surgery averages 65% to 70%.

What are the long-term outcomes of newborns with NEC?

Long-term follow-up of patients indicate that any long-term neurologic and other developmental problems are mainly related to the degree of immaturity of the patient. Poor nutrition from an inadequate amount of bowel is a significant problem despite all of the advances to date. The more advanced the NEC, the more the problems are with growth and development. In most large series, 25% to 30% of survivors have some form of impairment.

NEC in premature infants is one of the greatest challenges to neonatologists and pediatric surgeons. Despite remarkable and steady advances in overall care of such premature infants, diagnosis and management of newborns with NEC is complex and difficult. Decisions must be made on limited information because definite indications for operation frequently are lacking

SUGGESTED READINGS

Ahmed T, Ein S, Moore A: The role of peritoneal drains in treatment of perforated necrotizing enterocolitis: Recommendations from recent experience. J Pediatr Surg 33:1468-1470, 1995.
An excellent review of the when and how a drain should be placed into the abdomen in newborns with NEC.

Cooper A, Ross AJ, O’Neill JA, Schnaufer L: Resection with primary anastomosis for necrotizing enterocolitis: A contrasting view. J Pediatr Surg 16:743-746, 1983.
This study of 27 patients who had removal and anastomosis (sewing together of the ends of the intestines) from a total series of 198 surgical cases indicated that the role of anastomosis is limited and risky in critically ill, premature infants with multiple problems.

Ehrlich PF, Sato TT, Short BL, Hartman GE: Outcome of perforated necrotizing enterocolitis in the very low-birth weight neonate may be independent of the type of surgical treatment. Am Surg 67:752-756, 2001.
These authors looked at 70 surviving infants weighing less than 1000 g in terms of the complications and mortality (death rate) and found that it is best to tailor the treatment according to the individual patient situation.

Grosfeld JL, Cheu H, Schlatter M, et al: Changing trends in necrotizing enterocolitis. Ann Surg 214:300, 1991.
This large series shows reduced mortality for surgical NEC. The authors point out that even “micropremies” have satisfactory survival similar to more mature infants. The study points out the poor outcome when large amounts of intestine are dead and when air is seen in the portal vein.

Musemeche CA, Kosloske AM, Ricketts RR: Enterostomy in necrotizing enterocolitis: An analysis of techniques and timing of closure. J Pediatr Surg 22:479, 1987.
This is the only study that examines when the stoma should be closed. Closure less than 3 months after creation of the stoma did not increase the complication rate.

Moss RL, Dimmitt RA, Henry MCW, et al: A meta-analysis of peritoneal drainage versus laparotomy for perforated necrotizing enterocolitis. J Pediatr Surg 36:1210, 2001.
A summary is provided of the indications for placing a drain into the abdomen instead of making a large incision and removing any dead intestine for the management of NEC with perforation (rupture).

O’Neill JA: Necrotizing enterocolitis. In Puri P (ed): Surgery and Support of the Premature Infant. Basel, Karger 1985, pp 40-49.
This chapter reviews the cause of NEC, supportive care, indications for operation, and the various approaches available for management.

Schwartz MZ, Hayden CK, Richardson CJ, et al: A prospective evaluation of intestinal stenosis following necrotizing enterocolitis. J Pediatr Surg 17:764, 1983.
This study looks at the time course and incidence of narrowing of the intestine resulting from NEC, including many cases that were asymptomatic and resolved on their own.

Article and graphics adapted from O'Neill: Principles of Pediatric Surgery. © 2003, Elsevier.