Short bowel syndrome

What is short bowel syndrome?

The normal length of small bowel in an adult measures between 275 to 850 centimetres.¹ Around 9 litres of fluid passes through the small bowel daily and about 7 litres of those fluids are absorbed in the small bowel.

The absorption of most nutrients occurs in the first 100 centimetres of the jejunum. B12 and bile salts are absorbed in the last 100 centimetres of the ileum; magnesium is absorbed in the terminal ileum and proximal colon; water and sodium absorption occur throughout the bowel.

Short bowel syndrome (SBS) in adults is defined as less than 180 to 200 centimetres of remaining small bowel leading to malabsorption and malnutrition and the need for nutritional and fluid supplements. There is currently no accepted definition for SBS in children. The most frequent cause is surgical resection.

What causes short bowel syndrome? (Pathophysiology)

The manifestations of SBS are due to:²

• Loss of absorptive surface area.

• Loss of site-specific transport processes.

• Loss of site-specific endocrine cells and gastrointestinal hormones.

• Loss of ileocaecal valve.

Loss of large amounts of small intestinal absorptive mucosa results in malabsorption of water, electrolytes and nutrients. It also results in failure of resorption of the liquid produced by the gastrointestinal tract itself. This scenario is being increasingly referred to as 'intestinal failure'.³

Some 8,000-9,000 ml of fluid per day are produced, of which the normally functioning bowel retains all but 100-200 ml. One feature of SBS is thus the production of large amounts of liquid stool. The situation may be compounded by colonisation with bacteria.

Loss of significant lengths of ileum results in reduction of bile salt reabsorption, resulting in steatorrhoea.

SBS is not an inevitable consequence of loss of a significant amount of bowel. Other factors which come into play include:

• The length of premorbid bowel.

• Which segment of bowel is lost.

• The age of the patient at the time the bowel was lost.

• The remaining length of small and large intestine.

• Whether the ileocaecal valve is present or absent.

Three physiological changes may be identified.

• Acute phase - immediately after bowel resection. It is associated with malnutrition and fluid and electrolyte loss.

• Adaptation phase - 2-4 days after bowel resection, histological changes result in improved absorption and may influence the amount of parenteral nutrition required.

• Maintenance phase - the absorptive capacity of the bowel recovers to a greater or lesser extent. The degree of recovery will dictate the management of the patient in terms of the need for parenteral nutrition and nutritional supplements.

How common is short bowel syndrome? (Epidemiology)⁴

• The patient profile has changed over the years. Bowel strangulation and midgut volvulus were common aetiologies in the first decades of the twentieth century.

• By the 1950s and 1960s, the common causes had become mesenteric vascular accidents, including thrombosis and embolism of the superior mesenteric artery.

• The most common aetiology in adults is currently Crohn's disease.

• About 15% of people who have had gut resection develop SBS.

• There are no data on intestinal failure secondary to SBS, but extrapolated figures of home parenteral nutrition centres and single-centre studies suggest an incidence of 3-4 per million.

Symptoms of short bowel syndrome (presentation)⁵

History

The presenting history is usually diarrhoea and this may be coupled with weight loss, fatigue, malaise and lethargy.

The past history may be highly significant and may include Crohn's disease, or a history of several intestinal resections, a major abdominal catastrophe or vascular accident (eg, midgut volvulus or embolus of the superior mesenteric vessels.

Vitamin and mineral deficiency can cause:

• Night blindness and xerophthalmia (vitamin A).

• Paraesthesias (vitamins D and E, calcium, magnesium).

• Tetany (vitamins D and E, calcium, magnesium).

• Ataxic gait and visual disturbance due to retinopathy (vitamin E).

• Spontaneous bruising or prolonged bleeding (vitamin K).

• Dyspnoea, exertion and lethargy (vitamin B12, folic acid, iron).

• Anorexia.

Examination

Several features giving a clue to the diagnosis may be revealed by examination. These relate to the following nutritional abnormalities:

• Protein loss and malnutrition - there may be temporal wasting, loss of digital muscle mass, peripheral oedema, dry flaky skin, blunt lingual papillae and prominent ridges in the nails. Poor growth performance in children is characteristic.

• Deficiency of essential fatty acids (linoleic and linolenic) - growth restriction, dermatitis, alopecia.

• Vitamin A deficiency - corneal ulcerations, growth delays.

• B complex vitamins in general - stomatitis, cheilosis and glossitis.

• Vitamin B1 deficiency - oedema, tachycardia, ophthalmoplegia, depressed deep tendon reflexes.

• Vitamin B6 deficiency - peripheral neuropathies (also a feature of B12 deficiency) and seizures.

• Vitamin D depletion - poor growth, bowed extremities.

• Vitamin E deficiency - if severe, this can result in ataxia, oedema and depressed deep tendon reflexes.

• Vitamin K deficiency - petechiae, ecchymoses, purpura, or outright bleeding diatheses.

• Iron deficiency - pallor, spooned nails, glossitis.

• Zinc deficiency - angular stomatitis, poor wound healing, alopecia, scaly erythematous rash around the mouth, eye, nose and perineum.

Differential diagnosis

This may be wide-ranging and depending on presentation may include:

• Causes of chronic diarrhoea.

• Causes of malabsorption.

• Causes of growth failure.

Diagnosing short bowel syndrome (investigations)¹

Laboratory tests

• FBC - to check for anaemia; the type of anaemia may give a clue as to the nature of any deficiency (ie macrocytic or microcytic).

• Albumin - low albumin may indicate poor nutritional status whilst a high level may be seen in dehydration.

• LFTs - persistently elevated liver enzymes may indicate parenchymal damage. This should be differentiated from the transient elevation seen in patients on parenteral nutrition.

• Electrolytes - these may indicate dehydration and also need to be monitored in patients on parenteral nutrition in order for any abnormal levels to be corrected.

• Creatinine - may signal deteriorating renal function and suggest a change in nutritional support.

• Serum calcium, magnesium and phosphorus - to detect deficiencies which can affect many metabolic processes.

• Serum vitamin, mineral and trace element levels - to detect any deficiency.

• Coagulation profile - INR, prothrombin time (PT) and activated partial thromboplastin time (aPTT) should be assessed to exclude coagulopathy associated with hepatic dysfunction, especially in patients being considered for surgery.

Imaging

• Plain abdominal Xray - to exclude signs of ileus or obstruction and provide information on bowel status.

• Upper gastrointestinal series with small bowel follow-through - to identify areas of stricture and assess the appearance of small bowel mucosa. In the recovery stage, dilation of the bowel indicates that the adaptation phase has been reached.

• Abdominal CT scan with contrast - useful for identifying bowel obstruction, imaging the liver (and any consequent cirrhosis or early signs of liver dysfunction).

• Abdominal ultrasound - to exclude biliary sludge or gallstones, which may be associated with SBS.

Other tests

• Bone densitometry - to exclude metabolic bone disease which may develop as a consequence of calcium and vitamin D deficiency.

• Liver biopsy - in patients with abnormal LFTs. A variety of associated conditions may be found, including cholestasis, fatty change, non-alcoholic steatohepatitis and cirrhosis.

Associated diseases

Adults

• Crohn's disease.

• Radiation enteritis.

• Mesenteric vascular accidents.

• Trauma.

• Recurrent intestinal obstruction.

Children

• Necrotising enterocolitis (the most common cause).

• Ischaemic bowel infarction.

• Intestinal atresias.

• Intestinal volvulus.

• Congenital short small bowel.⁶

• Gastroschisis.

• Meconium peritonitis.

Managementof short bowel syndrome⁷

Interventions that may improve quality of life among patients dependent on parenteral nutrition and their carers include patient education, affiliation with support groups, treatment of concomitant symptoms and pharmacotherapies that decrease parenteral nutrition requirements.⁸

Medical¹

Most patients are treated with total parenteral nutrition (TPN) in the early stages. A decision is then taken as to whether the patient needs limited specialised enteral therapy or prolonged TPN. This will depend on the length and function of the remaining intestine and the mechanisms influencing transit time, including the functioning of the ileocaecal valve and colon. A combination of TPN and enteral feeding is often tried as this facilitates the discontinuation of TPN at the earliest possible stage.

Haemodynamic considerations are important and the volume of fluid replaced should be calculated according to the amount obtained from nasogastric suctioning and stool plus insensible losses. This volume should be added to the patient's usual daily maintenance volume. Urine output should be at least 1 litre daily.

Parenteral nutrition should provide adequate protein, calories, macronutrients and micronutrients. The time for adaptation, when improved absorption occurs, is controversial. Some authorities hold that maximal adaptation can take up to a year, others that little improvement is to be obtained after three months.

Excessive fluid and electrolyte loss (usually occurring in the first week after extensive intestinal resection) requires resuscitation with fluids, parenteral nutrition or both. Subsequent fluid replacement should be dictated by the amount of stool or ostomy output.

Levels of vitamins A, D, E and K and trace metals should be measured at regular intervals and replaced as appropriate.

Hypersecretion - usually noted within the first twelve months of resection - should be treated with an H₂-receptor antagonist or proton pump inhibitor.

The introduction of enteral feeding as soon as possible encourages bowel adaptation and may reduce the amount of time that parenteral feeding is required.⁹ Small amounts of oral food are introduced gradually.

Patients who have lost large amounts of ileum or colon may have significant fluid loss and may require prolonged intravenous fluid therapy.

A recombinant analog of glucagon-like peptide-2 (teduglutide) has been shown to result in a significant reduction in the requirement of intravenous fluids/parenteral nutrition.^{10 11} The National Institute for Health and Care Excellence (NICE) has recommended teduglutide as an option for treating SBS in people aged over 1 year, where it is provided under a commercial agreement.¹²

Probiotics do not have a protective role in preventing infection and protocol-based approaches with multidisciplinary teams have been shown to improve outcomes.¹³

Surgical

The treatment of SBS has to be individualised according to the clinical status of individual patients, and the decision on whether to resort to surgery and what operation to perform, depends upon many factors.

For patients with SBS, surgery can play an important role in preventing, mitigating, and, in some cases, reversing intestinal failure.¹⁴ There are several surgical options for management, including construction of intestinal valves or reversed intestinal segments, interposition of segments of colon, or intestinal lengthening procedures.¹⁵

In general, surgery is indicated as a last resort when all other therapeutic options, including parenteral and enteral feeding and pharmacological bowel compensation, have been tried. In some patients, operation may be required because of complications of prolonged parenteral nutrition or stasis of enteric content and bacterial overgrowth.

Surgery can be divided broadly into non-transplant surgery, transplant surgery without organ transplantation and combined intestinal and organ transplantation.

Non-transplant surgery
Various procedures have been tried to a greater or lesser degree of success. These include connecting residual small bowel to the colon to maintain intestinal integrity, intestinal lengthening and tailoring (the Bianchi procedure), tapering for dilated segments, strictureplasty, creation of intestinal valves or reversed bowel segments to reduce rapid transit time. It is likely that as these procedures improve, this type of surgery will become less of a 'last resort' and more of an option for those patients faced with long-term parenteral feeding.^{16 17} One study of 53 patients undergoing the Bianchi procedure reported a high survival rate, weight gain and a high quality of life.¹⁸ Bowel lengthening is technically feasible in over half of adult patients with SBS.

Transplant surgery¹⁹

• Intestinal transplantation: this has developed considerably over the last decade and results in adults are now similar to solid organ transplants.¹⁹ SBS is the leading indication (60-65%) for intestinal transplant in both adults and children.

• Isolated intestinal transplantation: this is mainly indicated for patients who have reasonable liver function or significant liver disease that has not progressed to cirrhosis. It may also be appropriate for patients who have significant fluid losses and who have episodes of frequent, severe dehydration despite appropriate medical management.

• Combined intestinal and organ transplantation: this is indicated for patients with SBS and end-stage liver failure. Renal transplantation may also be combined in appropriate patients.

Complications of short bowel syndrome

• Infection related to the indwelling venous feeding catheter.²⁰

• Thrombosis precluding adequate access for feeding.

• Complications of any underlying condition - eg, liver disease.

• Chronic complications outside of the gastrointestinal tract may include hepatobiliary disease, metabolic bone disease, lactic acidosis and kidney stone formation.²¹

General complications of surgery include haemorrhage, wound sepsis, postoperative pulmonary dysfunction, acute kidney injury and pulmonary embolism.

Complications of non-transplant surgery include:

• Bowel obstruction.

• Bowel necrosis.

• Bowel dysmotility and dysfunction.

• Anastomotic disruption.

• Stasis of intestinal contents with or without bacterial overgrowth.

Patients who undergo transplant surgery are at risk of all of the above but, in addition, may also develop:

• Acute rejection.

• Chronic rejection.

• Hepatic, portal, or mesenteric vein thrombosis.

• Systemic sepsis with ordinary pathogens or opportunistic organisms (eg, cytomegalovirus).

• Lymphoproliferative disorders or malignancies.

Prognosis

The prognosis is dependent on the underlying cause, the severity of SBS, the adaptation in the remaining bowel, the nature of any comorbidities and the effectiveness of management provided.²²

The most common cause of death of patients on TPN is liver failure, consequent upon chronic hepatic parenchymal damage.