A MECHANICAL IMPEDIMENT TO INTESTINAL FLOW; PHYSIOLOGICAL EFFECTS ON INTESTINAL ABSORPTION

Surgical options to enhance intestinal function in patients with short bowel syndrome

PURPOSE OF REVIEW

This review will provide the practitioner with an understanding of the spectrum of nontransplant surgical options for managing patients with short bowel syndrome (SBS).

RECENT FINDINGS

Intestinal lengthening procedures are a promising therapy to allow autonomy from parenteral nutrition. The recently described serial transverse enteroplasty is an effective procedure that is easier to perform and has similar outcomes to the more standard longitudinal lengthening procedure described by Bianchi.

SUMMARY

There are several surgical options for management of the SBS, including construction of intestinal valves or reversed intestinal segments, interposition of segments of colon, or intestinal lengthening procedures. The choice of technique is dictated by the patient's underlying pathophysiology and includes such factors as intestinal transit time, length of remnant bowel, presence of intact colon, and degree of small bowel dilation. Nontransplant surgical interventions are important adjuncts to the elimination of parenteral nutrition dependence and need for intestinal transplantation.

Management of the short bowel syndrome in the pediatric population

The short bowel syndrome in the pediatric population most commonly results from neonatal necrotizing enterocolitis. Multiple remedial surgical procedures have been developed to manage the rapid intestinal transit, decreased mucosal surface area, ineffective peristalsis, and short intestinal length in these patients. Despite significant morbidity, the overall outcome is favorable and warrants aggressive nutritional support, medical management, and surgical intervention in selected patients.

Mucosal morphology in isolated bowel segments: importance of exposure to luminal contents

An isolated bowel segment (IBS) is a loop of intestine that has been freed from its mesenteric attachment after the development of vascular collaterals between the antimesenteric surface of the gut and the host organ. Surgical creation of such artificially vascularized isolated bowel segments is of interest to researchers for a variety of studies, and may be useful in the treatment of short bowel syndrome, allowing longitudinal division of the remaining small bowel to double its length. We created four surgical variants to study the ability of the collateral blood supply to maintain mucosal integrity in the presence or absence of normal luminal contents. In all groups, a collateral blood supply was created in a 5- to 7-cm segment of adult rat jejunum by hepatoenteropexy (Iowa model II). In Thiry-Vella (T-V) and isolated bowel segment (IBS) rats, this segment was exteriorized at both ends to exclude luminal contents. Control and IBS in continuity (IBS-C) loops were left in continuity. The mesentery of IBS and IBS-C rats was divided 5 weeks later, leaving the experimental segment entirely dependent on the collateral circulation. All animals were harvested at 7 weeks after the initial surgery. Tissues were analyzed for mucosal weight, protein content per centimeter of bowel, length of villi, depth of crypts, DNA content, and sucrase activity. We found that segments retaining luminal continuity had significantly higher mucosal weight and DNA content per centimeter of bowel compared with exteriorized loops.

Intestinal transit time is delayed by artificial sphincters after massive enterectomy in dogs

Artificial sphincters were created in three groups of dogs after the resection of 87.5 percent of the intestine in each animal. Intestinal transit time was measured after 6 weeks by observing the passage of a radiopaque medium through the animals' intestinal tracts. No statistically significant differences were found between the intestinal transit times of dogs with one artificial sphincter and control animals. In dogs with two artificial sphincters there was a delay in the radiologically monitored intestinal transit time that was statistically significant compared with that of the control group.

Surgical therapy for the short bowel syndrome

The introduction of total parenteral nutrition has resulted in more patients surviving massive intestinal resection. Long-term parenteral nutrition is expensive, has potential complications, and causes inconvenience for the patient. Therefore, interest persists in surgical therapy for the short bowel syndrome. The goals of surgical therapy in the short bowel syndrome are to slow intestinal transit, increase the area of absorption, and reduce gastric hyperacidity. Patients with sufficient absorptive area, but rapid intestinal transit, benefit from antiperistaltic segments or colon interposition. Intestinal valves yield inconsistent results. Recirculating loops are associated with prohibitive morbidity and mortality. Experience with intestinal pacing is limited. Patients with dilated bowel segments may benefit from intestinal tapering or lengthening. Growing neomucosa holds promise but has not been evaluated clinically. Recent improvement in the results of intestinal transplantation in animals may warrant clinical trials. The efficacy of H2 receptor antagonists makes procedures for reducing gastric hyperacidity less necessary. None of the operations to treat the short bowel syndrome are sufficiently safe and effective to recommend their routine use. Operations should be performed only on selected patients to achieve specific goals. Although investigation continues, our emphasis should continue to be conservation of as much of the intestine as possible when massive resection is necessary.

An experimental model of a submucosally tunnelled valve for the replacement of the ileo-cecal valve

An enteric valve to prevent colonic content reflux and to prolong small bowel transit time was created by passing small bowel through a submucosal tunnel in the colon. Barium enema, Gl tract series, and iso- and antiperistaltic pressure measurements showed the valve to be of competence equal to the ileo-cecal valve. Late pathological examination revealed a patent valve with minimal scar formation. The optimal submucosal tunnel length was between 4 and 6 cm. This valve can, theoretically, increase the absorptive capacity in short bowel syndrome and may serve as a substitute for the critically important ileo-cecal valve.

Artificial sphincters as surgical treatment for experimental massive resection of small intestine

A modification of the technique of Schiller, DiDio, and Anderson was adopted by extending removal of the longitudinal layer of the muscular coat to the entire perimeter of a segment of the small intestine in dogs, resulting in the construction of artificial sphincters, to assist animals undergoing enterectomy. The creation of one or two artificial sphincters prolonged the survival of dogs undergoing massive resection of the small intestine (87.5 percent of the total length).