I have finally kum to the koncluzion that a good reliable sett of bowels is wurth more tu a man than enny quantity ov brains.

Josh Billings, 1818 - 85

The short bowel syndrome is characterized by:

1.Inadequate length of intestine

2.Diarrhoea

3.Steatorrhoea

4.Weight loss

5.Nutritional deficiency

6.Rapid intestinal transit

7.Hypergastrinaemia.

The syndrome can result from congenital deficiency of the intestine or may follow surgical resection for infarction or otherwise incurable disease (Table 1) 318. The majority of cases occur at the extremes of life: the most common cause in neonates is necrotizing enterocolitis, and in the elderly, mesenteric vascular occlusion.

The mean length of the adult small intestine in life has been estimated at 450 cm but it is 200 cm longer when measured at autopsy. Precise measurement is impossible because of constant variations in tone and contractility, which can be modified by drugs and by stretching, particularly along the antemesenteric border. Repeated measurements at laparotomy on the same patient invariably produce a different answer each time, so any claim to precision is entirely illusory. This fundamental problem has led to various opinions about both the length of intestine that can be resected without producing any detectable effects on intestinal absorption and the minimum length required to support life. Such claims are intrinsically pointless: much depends on the actual segments of bowel resected, the presence of an intact ileocaecal valve, and the colon and also on the normality or otherwise of the remaining intestine. As a general rule 50 per cent of the small intestine can be resected without causing severe or persistent malabsorption. As more intestine is removed the effects of malabsorption become progressively more severe, and lifelong dependence on medical support is inevitable for any patient with less than 100 cm of small intestine.

Resection is the only lifesaving option for patients with intestinal infarction, but intestine of doubtful viability can be conserved initially, a final decision being made at a planned laparotomy 24 h later. If more than half the small intestine is being resected such a ‘second look’ policy can save valuable inches of intestine and make a great difference to the long-term well-being of the patient. When the gut is diseased, but viable, the indications for intestinal resection are often relative: when the disease process is so extensive that less than 200 cm of intestine remain unaffected abnormal but functionally useful intestine can be conserved. In patients with Crohn's disease the recognition that limited resections and strictureplasties through diseased small intestine can be accomplished with uncomplicated healing has saved a number of patients from massive gut resection in the last 5 years. The more widespread use of such techniques would undoubtedly be beneficial, since prevention of the short bowel syndrome is preferable to its treatment.

The operative mortality for massive intestinal resection is high, particularly in the very young and old. Mortality is partly a consequence of the seriousness of the underlying pathology; acute mesenteric vascular occlusion still carries an overall mortality rate of more than 90 per cent. Intestinal resection is technically simple and many lives can be saved by adequate perioperative resuscitation and postoperative intensive monitoring and care. An understanding of the functional disturbances to be expected will allow appropriate corrective therapy to be instituted.

The pathophysiological changes that occur after massive resection of the small intestine can conveniently be considered in the three clinical phases which are commonly described: the acute, adaptive and chronic phases. Although this scheme is helpful in understanding the problems encountered in this complex disorder the phases are by no means distinct or exclusive and have many features in common.

This phase begins as soon as the postoperative ileus has recovered and lasts for about 4 weeks. Its characteristic feature is profuse watery diarrhoea with the passage of 5 to 10 litres of fluid daily per rectum or through the stoma. Severe fluid and electrolyte depletion is liable to occur and unless the loss is replaced as it takes place, a life-threatening situation can rapidly develop. These problems, which basically arise as a consequence of acute loss of much of the intestinal surface area and rapid intestinal transit, are particularly severe if the ileocaecal valve has been removed or if there has been associated colonic resection, since most normal fluid and electrolyte absorption occurs in the colon. The problem is compounded by gastric hypersecretion secondary to the hypergastrinaemia which commonly occurs. A large volume of acidic fluid is presented for intestinal absorption and delayed gastric emptying may result in vomiting or nasogastric aspiration of large volumes of fluid, causing further fluid and electrolyte depletion. Acute peptic ulceration (stress ulcer) is liable to develop and routine prophylaxis with H&sub2;-receptor antagonists and antacids is a sensible precaution.

In the early part of this phase the patient will also experience the catabolism which always occurs as part of the normal metabolic response to severe trauma. Fluid losses gradually diminish and, provided there has been adequate replacement of water and electrolytes, together with maintenance of calorie and nitrogen balance by parenteral nutrition, the patient will survive to enter the adaptive phase.

Intestinal adaptation to massive gut resection is a complex process which can take up to 2 years. The process is more effective in the ileum after proximal resection but occurs to a lesser extent in jejunum after distal intestinal resection. The changes affect the whole of the remaining bowel but are most marked in the small intestinal mucosa. Teleologically the process can be regarded as an attempt to increase total mucosal surface area and thereby increase intestine absorption. There is an increase in the circumference of the intestine, but only minimal increase in length. Villous height and crypt depth also increase due to epithelial hyperplasia, producing an increased number of absorptive cells, although the number of crypts and cells per unit area is unchanged. There is an increase in total mucosal cell turnover with an increased rate of migration of epithelial cells from crypt bases to the tips of the villi, but the life of an individual cell appears to remain the same. These changes are more marked in the ileum than in the jejunum, possibly because in the intact bowel the jejunum is already adapted for maximal absorption, whereas the ileum provides a reserve capacity to be called upon in the event of incomplete absorption of nutrients from the jejunum.

The terminal ileum serves a special role in the absorption of bile salts and vitamin B&sub1;&sub2;: this function is unique and is irreplaceable if the terminal ileum has been resected. Reduced bile salt reabsorption interrupts the enterohepatic circulation and causes a reduction in the bile salt pool. Gastric hypersecretion may reduce the pH of jejunal contents, allowing bile salt precipitation and inactivating pancreatic lipase. Pancreatic fibrosis can also arise as a consequence of massive intestinal resection, and all of these factors combine to cause steatorrhoea and reduced absorption of fat soluble vitamins.

Intestinal adaptation requires the presence of food in the intestinal lumen; together with bile and pancreatic secretions this appears to exert a trophic effect on intestinal mucosa. Humoral factors also play an essential part, along with gastrin and enteroglucagon, although the exact role of these and other hormones is unknown. Heterotopic autotransplants of intestinal mucosa in animals subjected to massive intestinal resection show hypertrophy, as does intestinal mucosa in parabiotic animals. Serum from animals with the short bowel syndrome also exerts a stimulatory effect on mucosal cells in tissue culture.

This lifelong phase begins when all of the adaptive changes which can occur have taken place. It is an intrinsically unstable state which is easily disturbed by relatively minor gastrointestinal upsets or intercurrent illness. Acute disturbances in the form of diarrhoea and fluid and electrolyte depletion may still occur, with intravenous fluid replacement being required even by patients who are usually able to survive on enteral nutrition alone. The characteristic problems of this phase are the long-term maintenance of a sufficient intake of calories and nitrogen and the prevention and correction of deficiencies of minerals, essential amino acids, fatty acids, vitamins, and trace elements which are liable to develop. The recognition of these deficiencies has become easier as experience with increasing numbers of patients surviving to this stage has built up.

The objective of management is to maximize the degree to which enteral nutrition contributes to the patient's total intake. Some individuals are able to maintain their health with an oral diet alone, others require frequent or intermittent supplementation by parenteral infusions. The most severely disabled will require total long-term parenteral nutrition: in these patients the preservation of venous access sites and prevention of cannula sepsis is a major priority.

A number of interesting specific problems are liable to develop in the chronic phase. Gallstones may form as chronic bile salt depletion results in the secretion of lithogenic bile and the precipitation of cholesterol in the gallbladder. There is also an increased incidence of urinary calculi, particularly oxalate stones. Oxalates in the diet are normally precipitated by calcium, but in patients with the short bowel syndrome calcium coprecipitates with unabsorbed fatty acids, leaving oxalate to be absorbed. This problem can be overcome by restriction of dietary oxalate intake and the administration of additional calcium supplements.

These form the mainstay of treatments in this condition and are dealt with in detail in Section 16.9 117.

Drugs have a limited role, apart from certain specific indications. H&sub2;-receptor antagonists may be required to control acid secretion in patients in whom persistent hypergastrinaemia is a problem. Their availability has largely removed the need for vagotomy, which is fortunate since in some patients the associated gastric drainage operation exacerbated diarrhoea by producing an incontinent stomach.

Antidiarrhoeal agents, particularly those which exert their effects by reducing gut motility, are frequently prescribed but any benefit produced is likely to be marginal, except in patients who have retained a useful length of colon.

Antibiotics may be required to treat gut or catheter sepsis but can have a deleterious effect on intestinal absorption by producing changes in the intestinal bacterial flora. They should be used with caution.

Many surgical procedures have been designed to treat the short bowel syndrome; most are experimental although several have been used in patients. The large number of operations described bears tribute to surgical ingenuity, although several procedures border on the fanciful. Attempts to slow intestinal transit and increase the duration of contact between gut contents and the absorptive mucosa have included interposing segments of stomach, small intestine, and colon, either isoperistaltic or reversed; construction of intestinal valves, baffles, or strictures; recirculating intestinal loops of various designs; attempts to provide a framework for the growth of intestinal neomucosa, and the use of retrograde electrical pacing of the intestinal myoelectrical activity.

Three surgical procedures may have some role to play in the practical clinical management of patients with the short bowel syndrome.

The optimum length of small intestine to reverse is around 10 cm: longer lengths increase the likelihood of development of intestinal obstruction. The effect of reversal has been assumed to be due to a delay in transit, with increased time available for absorption of nutrients from intestine proximal to the reversed segment. There may also be some increase in absorption from the reversed segment itself since retrograde perfusion of intestine has been shown to increase intestinal absorption. The usefulness of this operation will remain limited by technical difficulties and the reluctance to sacrifice even a small segment of intestine in patients who have so little.

This ingenious operation relies on the fact that the final distribution of blood supply from the mesenteric arcade is arranged so that each side of the intestine is independently vascularized. It is possible to separate the leaves of the mesentery, with its contained vessels, and divide the intestine longitudinally; anastomosis of the two tubes end to end doubles the length of intestine, while halving its circumference (Fig. 1) 990. Increase in intestinal absorption is predicted from the known fact that intestinal adaptation results in intestinal dilatation but little increase in length. This operation has been used to improve intestinal function in a number of infants.

Experimental intestinal allotransplantation has been investigated for more than 30 years, but the results of clinical application have, until recently, been disappointing. This treatment, which is discussed in detail elsewhere, holds out the best hope for the future of finally achieving a cure for patients with the short bowel syndrome (see Section 10.8.2 77).

Mitchell A, Watkins RM, Collin J. Surgical treatment of the short bowel syndrome. Br J Surg 1984; 71: 329–33.

Williamson RCN. Intestinal adaptation. N Engl J Med 298: 1393–1402; 1444–50.