Chapter 52 Necrotizing Enterocolitis
PATHOPHYSIOLOGY
Necrotizing enterocolitis (NEC) is the most common acquired gastrointestinal (GI) disease among sick newborns and is the single most common surgical emergency among newborns. It is a spectrum of illness that varies from a mild, self-limiting process to a severe disorder characterized by inflammation and diffuse or patchy necrosis in the mucosal and submucosal layers of the intestine. The cause of NEC has been the focus of research for over 30 years; although many theories have been proposed, however, the pathogenesis remains elusive and controversial. Most researchers agree that, regardless of the initiating event(s), the pathogenesis of NEC is multifactorial. At present, the etiology is thought to involve three major pathologic mechanisms occurring in combination to create a favorable disease environment: ischemic injury to the bowel, bacterial colonization of the bowel, and the presence of a substrate such as formula.
The hypoxic or ischemic injury causes a reduced blood flow to the bowel. Birth asphyxia, umbilical artery cannulation, persistence of a patent ductus arteriosus, respiratory distress syndrome, maternal cocaine abuse, and/or exchange transfusion may be the initiating factor(s). Intestinal hypoperfusion damages the intestinal mucosa, and the mucosal cells lining the bowel stop secreting protective enzymes. Bacteria, whose proliferation is aided by enteral feedings (substrate), invade the damaged intestinal mucosa. Bacterial invasion results in further intestinal damage because of the release of bacterial toxins and hydrogen gas. The gas initially dissects into the serosal and submucosal layers of the bowel (pneumatosis intestinalis). The gas may also rupture through the bowel into the mesenteric vascular bed, where it can be distributed to the venous system of the liver (portal venous air). The bacterial toxins in combination with ischemia result in necrosis. Full-thickness bowel necrosis results in perforation, with the resulting release of free air into the peritoneal cavity (pneumoperitoneum) and peritonitis. This chain of events is considered a surgical emergency.
INCIDENCE
The incidence of NEC varies considerably from nursery to nursery, both within a given geographic region and from region to region. These estimates may not accurately reflect the true incidence because of inconsistencies in definitions and in reporting of cases that are complicated by other confounding variables such as prematurity.
1. NEC occurs in 1% to 8% of all infants admitted to neonatal intensive care units.
2. NEC occurs in 6% to 10% of neonates with birth weights of less than 1500 g.
3. Seventy to 90% of cases occur in high-risk low birth weight infants.
4. Of infants who develop NEC, 10% to 25% are full-term. Many of these infants have specific risk factors such as asphyxia, intrauterine growth retardation (IUGR), umbilical vessel catheters, anatomic GI malformations, polycythemia, or other medical problems.
5. NEC is the third leading cause of neonatal death, with an overall mortality rate of 20% to 40%.
6. Extremely low birth weight infants (1000 grams) are particularly vulnerable, with reported mortality rates of 40% to 100%.
7. Mortality rates for term versus preterm infants are reported as 4.7% and 11.9%, respectively.
8. Of those who survive, approximately 23% experience long-term sequelae related to the GI tract.
9. There is a slightly increased prevalence in male infants.
10. In some studies, higher NEC rates are seen in African-American than in white or Hispanic neonates.
CLINICAL MANIFESTATIONS
The onset of NEC occurs most commonly between days 3 and 12 of life, but it can occur as early as the first 24 hours of life or as late as 90 days of age. The disease is characterized by a broad range of signs and symptoms that reflect the differences in severity, complications, and mortality of the disease. Typically, suspected NEC (stage I) consists of nonspecific clinical findings that represent physiologic instability and may resemble the findings of other common conditions in premature infants. These include the following:
3. Recurrent apnea and bradycardia
6. Increased pregavage gastric residuals
Proven NEC (stage II) consists of the aforementioned nonspecific clinical findings plus the following:
Advanced NEC (stage III) occurs when the infant becomes acutely ill with peritonitis and/or radiographic evidence of intestinal perforation. Associated signs and symptoms include the following:
LABORATORY AND DIAGNOSTIC TESTS
1. Laboratory results that reflect signs of sepsis include the following:
2. Radiologic findings are the cornerstone for confirming the diagnosis of NEC. The standard anteroposterior and left lateral decubitus (or cross-table lateral) radiographs may show any or all of the following:
3. Other diagnostic studies are emerging that may be of diagnostic benefit, particularly in the early stages of NEC. These include the following:
MEDICAL MANAGEMENT
In the absence of intestinal necrosis or perforation, aggressive medical management is the treatment of choice. Medical management is based on three general principles: (1) rest the bowel, (2) prevent continuing injury, and (3) correct or modify the systemic responses. Enteral feedings are discontinued, the GI tract is decompressed by low intermittent suction, and fluid and electrolyte imbalances are corrected. Intravenous antibiotic therapy directed against enteric flora is started; respiratory support, including intubation and ventilation, is often required; and efforts to support blood pressure and adequate perfusion to the bowel prevent continuing injury and help to correct systemic responses. Abdominal radiographs are obtained every 6 to 8 hours to monitor progression of the disease or detect perforation.
Although many infants can be treated successfully with medication and bowel rest, 25% to 50% require surgery. Indications for surgical intervention differ from institution to institution. A hallmark of successful surgical therapy is the anticipation of impending intestinal necrosis before perforation occurs to prevent gross peritoneal contamination. Evidence of progressive deterioration and ongoing necrosis is noted in worsening metabolic acidosis, respiratory failure, thrombocytopenia, oliguria, shock, and increasing abdominal wall distention. Indications for immediate surgical intervention are (1) pneumoperitoneum, (2) presence of portal venous air, (3) abdominal wall erythema or edema, and (4) intestinal gangrene (positive results on test of abdominal paracentesis specimen).
The principles of surgical management include (1) intestinal decompression, (2) careful examination of bowel with resection of perforated or unquestionably necrotic tissue, (3) preservation of as much bowel as possible, (4) preservation of the ileocecal valve if possible, and (5) preservation of bowel of questionable viability, with creation of a stoma proximal to this bowel. Marginally viable bowel may not be removed during the initial procedure; rather, resection may be deferred, with a follow-up second-look operation carried out in 24 to 48 hours to reassess bowel viability.
The type of surgical procedure required depends on the extent of bowel necrosis. If a short segment of necrotic bowel is present, a primary anastomosis may be adequate. Extensive necrosis or necrosis in a variety of areas may necessitate resection and placement of an enterostomy. If an extensive amount of necrotic bowel is resected, the infant may be left with an insufficient length of bowel for digestion, which causes malabsorption, failure to thrive, and short bowel syndrome.
The timing of stoma closure is somewhat arbitrary. If the infant is thriving on enteral feedings and is gaining weight, the stoma is usually closed at 3 to 5 months. A very proximal stoma that necessitates TPN or one that causes serious fluid and electrolyte problems should be closed sooner, usually after 4 to 6 weeks. If a stricture is found, it is resected during the procedure to close the stoma, and complete intestinal continuity is reestablished.
NURSING INTERVENTIONS
1. Monitor cardiac and respiratory status (may need to monitor as often as every hour during acute phase of disease).
2. Observe and report signs of change in cardiac status.
3. Observe and report signs of change in respiratory status.
4. Administer antibiotics as ordered.
5. Promote and maintain adequate body temperature.
6. Assess and maintain optimal hydration status.
7. Administer pain medications as ordered.
8. Promote process of attachment between parents and infant.
9. Provide developmentally appropriate stimulation activities (see relevant section in Appendix F).
Preoperative Care
Postoperative Care
1. Monitor infant’s response to surgery.
2. Monitor for and report signs and symptoms of complications.
3. Promote and maintain fluid and electrolyte balance.
4. Provide dressing care; maintain integrity of surgical site and stoma area.
5. Protect infant from infection.
6. Promote comfort and minimize pain.
7. Provide emotional support to parents during infant’s hospitalization.
Discharge Planning and Home Care
1. Encourage parents to express concerns about outcomes of surgery.
2. Refer to specific institutional procedures for information to be distributed to parents about home care.
3. Instruct parents regarding signs of intestinal obstruction, strictures, poor tolerance of feedings, and impaired healing processes.
4. Instruct parents about follow-up techniques to promote optimal surgical outcomes.
5. Provide family with name of physician to contact for medical or health care follow-up.
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