Understanding Neonatal Bowel Obstruction: Building Knowledge to Advance Practice Nicole T. de Silva, RN, MSc Jennifer A. Young, RN, MN Paul W. Wales, MD, MSc, FRCS(C) EONATA L INTESTINAL OBSTRUCTION ARISES FROM the tract is to transport enteral nutrients, fluids, and gases so Nvarious congenital anomalies of the gastrointestinal that digestion may occur. Knowledge of some key anatomic (GI) tract, as well as from acquired conditions. Common landmarks and structures is essential to understanding the clinical features include a history signs and symptoms that present of polyhydramnios, vomit- when the GI tract becomes ing, abdominal distension, and ABSTRACT obstructed (Figure 1). The GI failure to pass meconium in Providing care to neonates with bowel obstruction tract can be divided into three the first 24–48 hours of life. A requires a basic understanding of gastrointestinal (GI) major anatomic and functional detailed history, careful physi- anatomy and functional landmarks as well as knowledge of areas: (1) the proximal GI tract, the pathophysiology associated with intestinal blockage. cal examination, and subse- including the oral cavity, the Early recognition and prompt diagnosis necessitate astute quent radiographic imaging and assessment of common presenting symptoms and accurate esophagus, and the stomach; investigations help the neonatal interpretation of diagnostic investigations. Initial medical (2) the small intestine, made up nurse and nurse practitioner to management is focused primarily on gastric decompression of the duodenum, the jejunum support the infant appropriately and maintenance of fluid and electrolyte balance. This that begins just distal to the lig- in the face of a potential life- article describes features of the neonatal GI tract and ament of Treitz, and the ileum; threatening event. This article is discusses common causes of neonatal bowel obstruction. and (3) the large bowel, includ- intended to advance the knowl- ing the cecum with appendix, edge of neonatal nurses regard- the colon, and the rectum. The ing the diagnostic evaluation and initial management of smooth muscle (circular and longitudinal) layers of the GI infants with suspected intestinal obstruction. To understand tract are innervated by nerve cells called ganglia. In normal the etiology of symptoms, clinical presentation, and diag- circumstances, impulses from the ganglion cells result in nostic methods, health care providers must know the basic rhythmic constriction and relaxation of the bowel wall (peri- anatomy of the GI tract. Also reviewed here are the common stalsis), thus propelling the GI tract contents distally.1 causes of congenital intestinal obstruction that occur between Transition zones consisting of muscular tissue, referred the gastric outlet and the anus. to as valves or sphincters, act as “gatekeepers” or “brakes” to control the transit time of nutrients from one functional area ANATOMIC AND FUNCTIONAL to another. The flow of nutrients is slowed to allow enough LaNDMARKS OF THE GI TRACT time for the digestive process to occur. The most proxi- The GI tract is a conduit that extends from the proximal mal brake is the pylorus, which is positioned between the oral cavity to the distal rectum and anus. The purpose of stomach and the duodenum. The more distal brakes include Accepted for publication May 2005. 25 Years N EONATAL N ETWORK VOL. 25, NO. 5, SEPTEMBER/ O CT O B E R 2 0 0 6 3 0 3 FIGURE 1 n Selected gastrointestinal anatomy. Courtesy of The Hospital for Sick Children, Toronto, Ontario. the ileocecal valve, which lies between the small and large the common bile duct. Bile is stored in the gall bladder when intestine, and the anal sphincter and anus, which hold waste produced in excess. The gall bladder secretes bile into the in the rectum in preparation for evacuation from the body. common bile duct, which empties into the second or descend- Knowing where these functional brakes are located is impor- ing part of the duodenum at the major papilla (ampulla of tant, particularly for the purpose of diagnostic imaging. Vater) a few centimeters distal to the pylorus.3 The bile tints Three main arteries that arise from the abdominal aorta GI fluid green, and the presence or absence of bile-stained supply the major regions of the GI tract. The foregut (pharynx, fluid is useful for evaluating the location of an obstruction. esophagus, stomach, and proximal duodenum before the opening of the bile duct) obtains its blood supply from the TYPES OF OBSTRUCTION celiac artery. The midgut (small intestine, cecum, appendix, A blockage anywhere along the GI tract may be struc- and ascending and proximal transverse colon) is supplied by tural (mechanical) or physiologic (functional) (Table 1). the superior mesenteric artery. The hindgut (distal transverse Mechanical obstructions are more likely to require opera- colon, descending colon, sigmoid, and upper rectum) is sup- tive repair than functional (or paralytic) obstructions, which plied by the inferior mesenteric artery.2 Vascular insufficiency usually require medical treatment. A mechanical obstruction from thrombosis, strangulation, or low flow states can disrupt is usually caused by an intramural structural anomaly, such as the arterial supply of the bowel and lead to ischemic injury or an atresia, a stenosis, or a web. (Table 2 provides definitions malformation during any phase of development. and illustrations.) Mechanical obstructions physically slow or Three accessory digestive organs secrete substances block the forward flow of gas, fluids, and nutrients within the directly into the proximal GI tract: the pancreas, liver, and lumen, either partially or completely. Mechanical obstruc- gall bladder (see Figure 1). The pancreas secretes digestive tions, whether intraluminal or extraluminal and whether enzymes that drain into the pancreatic duct and empty pre- partial or complete, result in a narrowing of the diameter of dominantly into the duodenum at the ampulla of Vater. The the intestinal lumen. liver produces bile, which is emptied into the duodenum via 25 Years N EONATAL N ETWORK 3 0 4 SEPTEMBER/ O CT O B E R 2 0 0 6 , VOL. 25, NO. 5 n TABLE 1 Secondary Method of Classifying Intestinal Obstruction* Fluid and Electrolyte Imbalance Mechanical In comparison to adults, neonates secrete large volumes Intraluminal (within bowel lumen) of gastrointestinal fluids and electrolytes for their weight. If Meconium ileus (complicated and uncomplicated) all of the gastric content is lost through vomiting, short-lived Intraluminal tumor masses compensation occurs through depletion of the extracellular Extraluminal (outside of bowel lumen) fluid volume.4 In general, the obstructed bowel continues to Bands (adhesive, congenital Ladd’s-malrotation) secrete fluid, but reabsorption of the fluid and electrolytes is Masses (tumors, lymphoid tissue, cysts—duplication, ovarian, mesenteric) compromised. The amount and type of fluid loss depends on Hernias (inguinal, diaphragmatic, internal) the location of the obstruction. The degree of obstruction Intramural (within bowel wall) (partial or complete) and the extent of the vascular response Atresia/web/stenosis of the bowel wall (e.g., decreased stroke volume, hypotension) are directly Strictures (postinjury—i.e., necrotizing enterocolitis, ischemic injury) related to the amount of the fluid deficit.5 Strangulating Intussusception obstructions produce large fluid and serum protein loss as a Volvulus result of transudation (ascites) from the intestinal lymphatics Hirschsprung’s disease and increased mucosal permeability.5,6 Imperforate anus Functional (Loss of Peristalsis) Bacterial Translocation Pseudo-obstruction (neuropathic or myopathic in origin) After delivery, the baby’s gut becomes rapidly colonized Ileus with bacteria, especially if feeding has occurred.7 Intestinal Sepsis obstruction can lead to sepsis secondary to the overgrowth of Electrolyte imbalance (hypocalcemia, hypokalemia) these enteric organisms.8,9 The multiplication of bacteria and Narcotic induced the production of endotoxins quickly result in saturation of Metabolic (hypothyroidism) the mesenteric nodes, the lymphatic system, and the venules Retroperitoneal hematoma and eventual bacterial penetration of the bowel wall (bacte- Meconium plug syndrome rial translocation) into the bloodstream.10–12 Postoperative (handling/trauma) Prematurity/immaturity Circulatory Disturbances * As conceptualized by the authors The nutrient vessels encircle the bowel with a fine network of capillaries emanating from the mesentery. In the pres- ence of distention that increases the intraluminal pressure, Functional (physiologic) obstructions are caused by blood shunts away from the capillary bed.13 Mucosal oxygen decreased intestinal motility due to a direct inhibition of consumption decreases, and capillary venous congestion the smooth muscle in the bowel wall. Consequently, distal occurs. As engorgement progresses, the arterial blood supply propulsion of the contents of the bowel fails or is slowed. A decreases, and ischemia/infarction occurs.14,15 The brunt of combination of mechanical and functional obstructions may the circulatory compromise is borne by the dilated bowel just occur. Overall, obstructions can be further subdivided by proximal to the point of obstruction.16,17 location within the GI tract: proximal (just before or after Intraluminal distention alone is not the primary cause the ampulla of Vater), mid (jejunoileal), or distal (colonic). of bowel ischemia and ulceration.