Digestive System Disorders

Chapter 96 Digestive System Disorders





Vomiting


Vomiting or, more often, regurgitation is a relatively frequent symptom during the neonatal period. In the 1st few hours after birth, infants may vomit mucus, occasionally blood streaked. This vomiting rarely persists after the 1st few feedings; it may be due to irritation of the gastric mucosa by material swallowed during delivery. If vomiting is protracted, gastric lavage with physiologic saline solution may relieve it.


When vomiting occurs shortly after birth and is persistent, the possibilities of intestinal obstruction, metabolic disorders, and increased intracranial pressure must be considered. A history of maternal polyhydramnios suggests upper gastrointestinal (esophageal, duodenal, ileal) atresia. Bile-stained emesis suggests intestinal obstruction beyond the duodenum but may also be idiopathic. Abdominal radiographs (kidney-ureter-bladder [KUB] and cross-table lateral views) should be performed in neonates with persistent emesis and in all infants with bile-stained emesis to detect air-fluid levels, distended bowel loops, characteristic patterns of obstruction (double bubble: duodenal atresia), and pneumoperitoneum (intestinal perforation). A contrast swallow roentgenogram with small bowel follow-through is indicated in the presence of bilious emesis.


Obstructive lesions of the digestive tract are the most frequent gastrointestinal anomalies (Chapters 311, 321, 322, and 324). Vomiting (and drooling) from esophageal obstruction occurs with the 1st feeding. The diagnosis of esophageal atresia can be suspected if unusual drooling from the mouth is observed and if resistance is encountered during an attempt to pass a catheter into the stomach. The diagnosis should be made before the infant has trouble with oral feedings and aspiration pneumonia develops. Infantile achalasia (cardiospasm), a rare cause of vomiting in newborn infants, is demonstrable radiographically as obstruction at the cardiac end of the esophagus without organic stenosis. Regurgitation of feedings because of continuous relaxation of the esophageal-gastric sphincter, or chalasia, is a cause of vomiting. Keeping the infant in a semi-upright position, thickening the feeding, or administering prokinetic drugs can control it.


Vomiting due to obstruction of the small intestine usually begins on the 1st day of life and is frequent, persistent, usually nonprojectile, copious, and, unless the obstruction is above the ampulla of Vater, bile-stained; it is associated with abdominal distention, visible deep peristaltic waves, and reduction or absence of bowel movements. Malrotation with obstruction from midgut volvulus is an acute emergency that must be not only considered but also urgently evaluated by an upper gastrointestinal contrast radiographic series. Radiographs of the abdomen show the distribution of air in the intestine, which may point to the anatomic location of an obstruction; malrotation can be identified only by contrast studies. Normally, air can be demonstrated by radiographs in the jejunum by 15-60 min, in the ileum by 2-3 hr, and in the colon by 3 hr after birth. Absence of rectal gas at 24 hr is abnormal. Persistent vomiting may occur with congenital diaphragmatic hernia. The vomiting associated with pyloric stenosis may begin any time after birth but does not assume its characteristic pattern before the 2nd-3rd wk. Vomiting with obstipation is a common early sign of Hirschsprung disease. Vomiting may occur with many other disturbances that do not obstruct the digestive tract, such as milk allergy, adrenal hyperplasia of the salt-losing variety, galactosemia, hyperammonemias, organic acidemias, increased intracranial pressure, septicemia, meningitis, and urinary tract infection. In many infants, it is simply regurgitation from overfeeding or from failure to permit the infant to eructate swallowed air. (See Chapter 315 for a discussion of gastric emptying and gastroesophageal reflux.)





Meconium Plugs


Lower colonic or anorectal plugs (Fig. 96-1) with a lower than normal water content may cause intestinal obstruction. Rarely, a firm mass of meconium may form elsewhere in the intestine and cause intrauterine intestinal obstruction and meconium peritonitis unrelated to cystic fibrosis (CF). Anorectal plugs may also cause mucosal ulceration and intestinal perforation. Meconium plugs are associated with small left colon syndrome in infants of diabetic mothers and with CF, rectal aganglionosis, maternal opiate use, and magnesium sulfate therapy for preeclampsia. The plug may be evacuated by glycerin suppository or rectal irrigation with isotonic saline. Enemas with the iodinated contrast medium Gastrografin usually induce passage of the plug, presumably because the high osmolarity (1,900 mOsm/L) of the solution draws fluid rapidly into the intestinal lumen and loosens inspissated material. Such rapid loss of fluid into the bowel may result in acute dehydration and shock, so it is advisable to dilute the contrast material with an equal amount of water, correct any existing dehydration, and provide intravenous fluids during and for several hours after the procedure. After removal of a meconium plug, the infant should be observed closely for the possible presence of congenital aganglionic megacolon.




96.1 Meconium Ileus in Cystic Fibrosis


Akhil Maheshwari and Waldemar A. Carlo


Impaction of meconium causes intestinal obstructions and may be associated with CF. The absence of fetal pancreatic enzymes in CF limits normal digestive activities in the intestine, and meconium becomes viscid and mucilaginous. It clings to the intestinal wall and moves with difficulty. The inspissated and impacted meconium fills the intestinal canal but is most concentrated in the lower part of the ileum. Clinically, the pattern is that of congenital intestinal obstruction with or without intestinal perforation. Abdominal distention is prominent, and vomiting becomes persistent. Infrequently, one or more inspissated meconium stools may be passed shortly after birth.


The differential diagnosis involves other causes of intestinal obstruction, including intestinal pseudo-obstruction and other causes of pancreatic insufficiency (Chapter 341). A presumptive diagnosis can be made on the basis of a history of CF in a sibling, via palpation of doughy or cordlike masses of intestines through the abdominal wall, and from the radiographic appearance. In contrast to the generally evenly distended intestinal loops above an atresia, the loops may vary in width and are not as evenly filled with gas. At points of heaviest meconium concentration, the infiltrated gas may create a bubbly granular appearance (Figs. 96-2 and 96-3). It is technically difficult to perform a sweat test in a neonate. Genetic testing confirms the diagnosis of CF.




Treatment for meconium ileus is high Gastrografin enema as described previously for meconium plugs. If the procedure unsuccessful or perforation of the bowel wall is suspected, laparotomy is performed, and the ileum opened at the point of greatest diameter of the impaction. Approximately 50% of these infants have associated intestinal atresia, stenosis, or volvulus that requires surgery. The inspissated meconium is removed by gentle and patient irrigation with warm isotonic sodium chloride or acetylcysteine (Mucomyst) solution through a catheter passed between the impaction and the bowel wall. Most infants with meconium ileus survive the neonatal period. If meconium ileus is associated with CF, the long-term prognosis depends on the severity of the underlying disease (Chapter 395).




96.2 Neonatal Necrotizing Enterocolitis




NEC is the most common life-threatening emergency of the gastrointestinal tract in the newborn period. The disease is characterized by various degrees of mucosal or transmural necrosis of the intestine. The cause of NEC remains unclear but is most likely multifactorial. The incidence of NEC is 1-5% of infants in neonatal intensive care units (NICUs). Both incidence and case fatality rates increase with decreasing birthweight and gestational age. Because very small, ill preterm infants are particularly susceptible to NEC, a rising incidence may reflect improved survival of this high-risk group of patients.




Pathology and Pathogenesis


Many factors may contribute to the development of a necrotic segment of intestine, gas accumulation in the submucosa of the bowel wall (pneumatosis intestinalis), and progression of the necrosis to perforation, peritonitis, sepsis, and death. The distal part of the ileum and the proximal segment of colon are involved most frequently; in fatal cases, gangrene may extend from the stomach to the rectum. Although NEC is a multifactorial disease primarily associated with intestinal immaturity, the concept of “risk factors” for NEC is controversial. The triad of intestinal ischemia (injury), enteral nutrition (metabolic substrate), and bacterial translocation has classically been linked to NEC. The greatest risk factor for NEC is prematurity. The disorder probably results from an interaction between loss of mucosal integrity due to a variety of factors (ischemia, infection, inflammation) and the host’s response to that injury (circulatory, immunologic, inflammatory), leading to necrosis of the affected area. Coagulation necrosis is the characteristic histologic finding in intestinal specimens. Clustering of cases suggests a primary role for an infectious agent. Various bacterial and viral agents, including Escherichia coli, Klebsiella, Clostridium perfringens, Staphylococcus epidermidis, astrovirus, norovirus, and rotavirus, have been recovered from cultures. Nonetheless, in most situations, no pathogen is identified. NEC rarely occurs before the initiation of enteral feeding and is much less common in infants fed human milk. Aggressive enteral feeding may predispose to the development of NEC.


Although nearly 90% of all cases of NEC occur in premature infants, the disease can occur in full-term neonates. NEC in term infants is often a “secondary” disease, seen more frequently in infants with history of birth asphyxia, Down syndrome, congenital heart disease, rotavirus infections, and Hirschsprung disease.



Clinical Manifestations


Infants with NEC have a variety of signs and symptoms and may have an insidious or sudden catastrophic onset (Table 96-1). The onset of NEC is usually in the 2nd or 3rd week of life but can be as late as 3 mo in VLBW infants. Age of onset is inversely related to gestational age. The 1st signs of impending disease may be nonspecific, including lethargy and temperature instability, or related to gastrointestinal pathology, such as abdominal distention and gastric retention. Obvious bloody stools are seen in 25% of patients. Because of nonspecific signs, sepsis may be suspected before NEC. The spectrum of illness is broad, ranging from mild disease with only guaiac-positive stools to severe illness with bowel perforation, peritonitis, systemic inflammatory response syndrome, shock, and death. Progression may be rapid, but it is unusual for the disease to progress from mild to severe after 72 hr.




Diagnosis


A very high index of suspicion in treating preterm at-risk infants is crucial. Plain abdominal radiographs are essential to make a diagnosis of NEC. The finding of pneumatosis intestinalis (air in the bowel wall) confirms the clinical suspicion of NEC and is diagnostic; 50-75% of patients have pneumatosis when treatment is started (Fig. 96-4). Portal venous gas is a sign of severe disease, and pneumoperitoneum indicates a perforation (Figs. 96-4 and 96-5). Hepatic ultrasonography may detect portal venous gas despite normal abdominal roentgenograms.




The differential diagnosis of NEC includes specific infections (systemic or intestinal), gastrointestinal obstruction, volvulus, and isolated intestinal perforation. Idiopathic focal intestinal perforation can occur spontaneously or after the early use of postnatal steroids and indomethacin. Pneumoperitoneum develops in such patients, but they are usually less ill than those with NEC.



Treatment


Rapid initiation of therapy is required for suspected as well as proven cases of NEC. There is no definitive treatment for established NEC, so, therapy is directed at giving supportive care and preventing further injury with cessation of feeding, nasogastric decompression, and administration of intravenous fluids. Careful attention to respiratory status, coagulation profile, and acid-base and electrolyte balances are important. Once blood has been drawn for culture, systemic antibiotics (with broad coverage based on the antibiotic sensitivity patterns of the gram-positive, gram-negative, and anaerobic organisms in the particular NICU) should be started immediately. If present, umbilical catheters should be removed, but good intravenous access is maintained. Ventilation should be assisted in the presence of apnea or if abdominal distention is contributing to hypoxia and hypercapnia. Intravascular volume replacement with crystalloid or blood products, cardiovascular support with fluid boluses and/or inotropes, and correction of hematologic, metabolic, and electrolyte abnormalities are essential to stabilize the infant with NEC.


The patient’s course should be monitored closely by means of frequent physical assessments; sequential anteroposterior and cross-table lateral or lateral decubitus abdominal radiographs to detect intestinal perforation; and serial determinations of hematologic, electrolyte, and acid-base status. Gown and glove isolation and grouping of infants at similar increased risks into cohorts separate from other infants should be instituted to contain an epidemic.


A surgeon should be consulted early in the course of treatment. Indications for surgery include evidence of perforation on abdominal roentgenograms (pneumoperitoneum) or positive result of abdominal paracentesis (stool or organism on Gram stain preparation from peritoneal fluid). Failure of medical management, a single fixed bowel loop on radiographs, abdominal wall erythema, and a palpable mass are relative indications for exploratory laparotomy. Ideally, surgery should be performed after intestinal necrosis develops but before perforation and peritonitis occur. In unstable premature infants with perforated NEC, peritoneal drainage can be cautiously considered as an alternative to exploratory laparotomy, although the best surgical approach in these infants remains unresolved. The type of surgical operation did not influence survival or other clinically important early outcomes in one multicenter study, but another large randomized trial showed that a majority of infants who were initially treated with peritoneal drains required a delayed secondary laparotomy. There are also some concerns about the long-term outcome (death or neurodevelopmental outcome) for infants treated with peritoneal drainage.


Patients with isolated intestinal perforation tend to have a lower birthweight, are less likely to be receiving oral feeding, and are prone to perforation at an earlier postnatal age than are patients with perforation related to NEC. In many patients with isolated intestinal perforation treated by drainage, no further surgical procedure is needed; a small subgroup may require later surgery to repair an intestinal stricture or fistula.





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Jun 18, 2016 | Posted by in PEDIATRICS | Comments Off on Digestive System Disorders

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