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Gross anatomic malformations are usually diagnosed during the first few days of life. Some are apparent on the initial physical examination, such as omphalocele, gastroschisis, diaphragmatic hernia, and imperforate anus. Others are manifested in the first few days of life as enteral feeding failure, intestinal atresia, microcolon, tracheoesophageal fistula, and meconium ileus. Other malformations present difficult diagnostic and therapeutic dilemmas after the neonatal period. Specific clinical problems are discussed in the following sections.
Malrotation of the intestine is related to incomplete rotation of the fetal midgut during migration into the abdominal cavity. This abnormal rotation can lead to either partial or complete duodenal obstruction by peritoneal (Ladd) bands or, more important, to volvulus of the midgut.[267] The midgut (duodenum to transverse colon) and its vascular supply hang on a single pedicle; if the pedicle twists, vascular infarction of the entire midgut can result. [268] Infants with omphalocele almost invariably have associated malrotation. Symptomatic infants and children usually have signs of high intestinal obstruction (bilious vomiting) or signs of an acute abdomen, intestinal performation, and sepsis. Treatment is surgical reduction and fixation of the volvulus with resection of nonviable bowel. Postoperative respiratory support and total parenteral nutrition are often required in infants who were severely compromised before surgery.
Meckel's diverticulum represents persistence of the omphalomesenteric or vitelline duct and comes to attention clinically as a cause of painless lower GI bleeding.[269] The site of bleeding is an ulceration in the bowel mucosa caused by the secretion of gastric acid. Although these hemorrhages are usually self-limited, massive and life-threatening hemorrhage has been reported. [270] The diagnosis is often one of exclusion and can be difficult to make. The technetium pertechnetate isotope scan is helpful only if gastric mucosa is present in the diverticulum. Therapy is supportive, with particular attention paid to blood replacement. The definitive therapy is surgical resection.
Hirschsprung's disease (congenital aganglionic megacolon) is characterized by absence of the parasympathetic ganglion cells in varying distal lengths of the rectum and colon.[271] Lack of these ganglion cells produces a relatively narrowed segment of bowel, and the normal proximal portion of bowel becomes distended. The resultant clinical symptoms can be relatively minor, with abdominal distention and stool retention, or severe, with toxic megacolon, peritonitis, and perforation. Toxic megacolon is usually manifested in younger children; reported mortality rates are as high as 75%.[272]
The diagnosis of Hirschsprung's disease can sometimes be made on the basis of the history and physical examination. Barium enema should reveal a narrowed segment with ballooning of the proximal part of the bowel. The definitive diagnosis is made by rectal/colon biopsy with observation for the presence or absence of ganglion cells. Treatment of toxic megacolon is both supportive, with meticulous volume re-expansion and antibiotic coverage, and definitive, with surgical decompression by creating a colostomy in the region of normal bowel.
Intestinal disorders can produce bleeding, obstruction, or inflammation with secondary problems of malabsorption
A specific disease that merits separate discussion is necrotizing enterocolitis. This fulminant neonatal disease is characterized by ulceration and necrosis of the small bowel and colon. The cause is unknown but probably multifactorial. The greatest risk factor for necrotizing enterocolitis is prematurity and probably involves a combination of intestinal ischemia, oral feeding, and pathogenic organisms. Umbilical artery catheters, perinatal asphyxia, respiratory distress syndrome, and persistent patent ductus arteriosus have all been implicated.[277] The incidence is on the rise, with 1% to 5% of infants in neonatal ICUs affected. Feeding intolerance, abdominal distention, and bloody stools are the most common initial signs. Intestinal obstruction, perforation, and sepsis may follow. Treatment consists of withholding enteral feeding, nasogastric decompression, intravenous fluids, hemodynamic support, administration of appropriate antibiotics, and surgical exploration if an acute abdomen with free air is evident. Peritoneal drainage may be helpful for very-low-birth-weight babies and those in extremis.[278] Total parenteral nutrition is often required for several weeks, and intestinal obstruction can occur weeks to months after a relatively benign course.[279] [280]
Hepatic failure can occur in patients with chronic or acute liver disease. The causes and clinical features differ; chronic liver failure can be caused by biliary atresia, inborn errors of metabolism (tyrosinosis, Wilson's disease, galactosemia, cystic fibrosis), or chronic inflammatory hepatitis. Children with chronic disease often have the signs and symptoms of synthetic dysfunction (malnutrition, hypoalbuminemia, abnormal coagulation), degradation dysfunction (icterus and hyperammonemia), and portal hypertension (hypersplenism and varices). Acute liver failure is most commonly caused by infectious hepatitis, types A and B. Toxic hepatic failure is a close second.[281]
Physical examination is important for the identification of liver and spleen size and for evidence of bleeding, edema, and other organ dysfunction. Laboratory evaluation should include a screen of synthetic function (albumin, prothrombin time [PT], partial thromboplastin time [PTT]), a degradation screen (bilirubin, ammonia), and values of all liver enzymes. Hepatic ultrasound, radio-graphic contrast studies, and liver biopsy are indicated on an individual basis.
Life-threatening complications of liver failure include acute bleeding, cardiovascular compromise secondary to massive intravascular hypovolemia from fluid shifts, and intracranial hypertension from the toxic encephalopathy. Treatment is expectant and supportive. A 10% dextrose infusion is used to guarantee an adequate carbohydrate supply. Low-protein diets tend to minimize ammonia production. Coagulation is supported with the administration of vitamin K, fresh frozen plasma, and platelets as required. Plasmapheresis with fresh frozen plasma and platelets can be used to improve coagulation while maintaining normovolemia. Oral lactulose and neomycin enemas are given in an attempt to decrease the enterohepatic cycle of ammonia production and absorption.[282] Cardiovascular and respiratory function should be closely monitored and supported as required.
It is important to anticipate the complication of intracranial hypertension. Serum ammonia levels are often used to monitor or track the neurologic dysfunction,[282] [283] but it is important to remember that it is unknown whether ammonia is the primary CNS toxin or just one of many chemical markers. Other specific and controversial therapies are used as well. Steroids have been proposed for some forms of inflammatory hepatitis. Exchange transfusions and plasmapheresis have been advocated to decrease the toxin load,[284] and although they have had variable results, to date no strong evidence has indicated that morbidity and mortality are changed with these interventions.[285] Patients with certain forms of acute hepatic failure, including those resulting from toxic as well as infectious causes, may be considered candidates for liver transplantation. [286]
Extrahepatic biliary atresia occurs once in every 8000 to 10,000 live births.[287] The atresia differs from patient to patient and involves variable degrees of obstruction or discontinuity of the biliary tree between the duodenum and the proximal branches of the hepatic ducts. Treatment is surgical (jejunal Roux-en-Y and portoenterostomy) and is tailored to the amount of extrahepatic bile duct architecture present. These Kasai procedures are most successful in patients operated on at an early age (before 6 to 9 months). This surgery is associated with many acute and chronic complications, including hepatic failure, ascending cholangitis, and cirrhosis with portal hypertension and varices. Despite these complications, the Kasai procedure persists because of the scarcity of suitable donor organs.[288]
Improved immunosuppressive drugs and surgical techniques have increased interest in and the success of liver transplantation. The perioperative and postoperative periods require a coordinated approach involving many disciplines: surgery, gastroenterology, anesthesia, immunology, and ICU staff. Reports to date suggest that although these children are critically ill, they do not pose unique clinical problems. Most of the clinical issues that arise can be anticipated. These children experience large blood losses and require massive replacement therapy in the operating room. Because of this situation, intravascular volume status, renal status, and hematology/coagulation profiles must be closely monitored, and basic liver failure therapy is indicated. The immunosuppression required for graft survival puts the patient at risk for infection with both "normal" and opportunistic organisms. Surveillance cultures and early aggressive antibiotic therapy are indicated. Perhaps the only unanticipated complication has been systemic hypertension, which appears to be unrelated to elevated CVP or pulmonary capillary wedge pressure. Many patients have required aggressive therapy (hydralazine, diazoxide, captopril).[289] [290] [291]
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