25. 1 Acute pancreatitis

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Содержание Historical aspects Mechanical Obstruction Paralytic Ileus

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HISTORICAL ASPECTS

Hippocrates observed and treated intestinal obstruction. Praxagoras (350 B.C.), who created an enterocutaneous fistula to relieve an obstruction, performed the earliest known operation for intestinal obstruction. Nonoperative treatment remained the general rule, however, and included reduction of hernias, opium for pain, orally administered mercury or lead shot to open the occluded bowel, electrical stimulation, and gastric lavage.

In the nineteenth century, amid considerable debate, surgical procedures became more frequent for intestinal obstruction. Most of the significant advances in the management of this disorder occurred after the turn of the twentieth century. Hartwell and Hoguet observed in 1912 that parenteral administration of saline solution prolonged the lives of dogs with intestinal obstruction. Administration of intravenous fluid has become a cardinal principle in the management of intestinal obstruction today. The second decade of the twentieth century saw the development of radiographic techniques for the diagnosis of intestinal obstruction. In the 1930s, nasogastric or intestinal tubes were employed to prevent or relieve intestinal distention in patients with intestinal obstruction. Antibiotics were added to the therapy of bowel obstruction in the 1940s and 1950s. Replacement fluids, intestinal decompression, antibiotics, and improvements in surgical and anesthetic techniques have reduced the mortality in simple intestinal obstruction; however, the recognition and treatment of strangulating intestinal obstruction remain important problems for surgeons today.

ETIOLOGY

When gastrointestinal luminal content is pathologically prevented from passing distally, intestinal obstruction exists. Mechanical occlusion of the bowel into its lumen or paralysis of the intestinal muscle, called paralytic ileus, may cause intestinal obstruction.

Mechanical Obstruction

Three types of abnormalities may produce mechanical obstruction.

1. Obstruction of the intestinal lumen may be caused by several kinds of disease, such as polypoid tumors of the bowel. Intussusception is an invagination of the bowel lumen, with the invaginated portion (the intussusceptum) passing distally into the ensheathing outer portion (the intussuscipiens) by peristalsis. Unrelieved intussusception can occlude the blood supply of the intussusceptum. In adults, intussusception is usually caused by an abnormality of the bowel wall, such as a tumor or Meckel's diverticulum; in infants and children, intussusception may occur without apparent anatomic cause. Large gallstones, which can enter the intestinal lumen via a cholecystoenteric fistula, can cause obturation to produce a rare condition called gallstone ileus.

Feces, meconium, or bezoars may obstruct the intestine. Bezoars occur more frequently in children, the mentally retarded, and the toothless, and in patients after gastrectomy.

2. Intrinsic bowel lesions producing intestinal obstruction are often congenital (atresia, stenosis, duplication); they occur most commonly in infants and small children and are described in Chapter 38. Strictures of the intestine may result from neoplasm, as in carcinoma of the sigmoid colon, or from inflammation, as in Crohn's disease. Rarely, one encounters iatrogenic strictures following intestinal anastomosis or radiation therapy.

3. Lesions extrinsic to the bowel cause intestinal obstruction. Occlusion of the intestine by adhesions from previous operations or inflammation is the leading cause of small intestinal obstruction. Adhesions may obstruct by kinking or angulation or by creating bands of tissue that compress the bowel. External hernias are the second most common cause of mechanical small intestinal obstruction. Inguinal, femoral, umbilical, and incisional hernias are important causes of bowel obstruction. The risk of intestinal obstruction is the principal reason for the elective repair of hernias. Internal hernias due to congenital abnormalities of the mesentery or to surgical defects in the mesentery occasionally cause bowel obstruction. Extrinsic masses such as neoplasms and abscesses may cause mechanical bowel obstruction. A volvulus is an extrinsic abnormality in which a portion of the alimentary canal rotates or twists about itself; the twist usually involves the blood supply of the twisted portion of the bowel. This abnormality can kink the gut and produce mechanical obstruction, frequently occluding the blood supply to the bowel. A volvulus usually accompanies an underlying abnormality; for example, midgut volvulus is caused by the mesenteric abnormality of malrotation. Cecal volvulus occurs when the cecum or right colon is on a mesentery rather than being retroperitoneal. Sigmoid volvulus develops when the sigmoid colon is abnormally long or redundant. Another type of volvulus occurs when adhesions fix the intestine to a point that acts as a pivot for the volvulus. The most common causes of intestinal obstruction in adults are adhesions, usually from previous operations, hernias, and neoplasms. Neoplasms are the most common cause of colon obstruction.

Paralytic Ileus

Paralytic ileus, a common disorder, occurs to some extent in most patients undergoing abdominal operations. Several neural, humoral, and metabolic factors cause this abnormality. Reflexes that inhibit intestinal motility, such as the intestinointestinal reflex, result from prolonged intestinal distention. Distention of other organs, such as the ureter, can inhibit intestinal motility. Spine fracture, retroperitoneal hemorrhage, or trauma can also produce paralytic ileus. A humoral factor in paralytic ileus is suggested by experiments in dogs, in which motility of transplanted (denervated) intestinal loops was inhibited during experimental peritonitis. The substances responsible for this phenomenon are unknown. Clinically, peritonitis causes paralytic ileus. Electrolyte imbalances, particularly hypokalemia, contribute to paralytic ileus by interfering with the normal ionic movements during smooth muscle contraction. Finally, ischemia of the intestine rapidly inhibits motility.