9. Short bowel syndrome

Kirstine Farrer and Lindsay Harper

LEARNING OBJECTIVES

By the end of this chapter the reader will be able to:

• Define intestinal failure and state the main nutritional consequences of short bowel syndrome in relation to the site of bowel resection;

• Describe the nutritional management for a patient with a high output enterostomy and how to monitor this type of patient;

• State the pharmacological action of medicinal agents used to treat short bowel syndrome and oral rehydration solutions;

• Identify appropriate extended roles for dietitians in gastrointestinal disease; and

• Demonstrate awareness of the current legal situation regarding non medical prescribing including patient group directions.

Historical context

This chapter aims to focus on the dietetic and pharmacological management of patients with intestinal failure and short bowel syndrome (SBS). Patients with type 1 intestinal failure, i.e. patients who require some parenteral support (perhaps only replacement of electrolyte fluids), may, with intensive dietetic and pharmacological intervention, obviate the need for long-term parenteral nutrition (PN).

In England there are two designated national centres for the management of acute intestinal failure (IF): one at Salford Royal NHS Foundation Trust, Manchester, and the other at St Marks Hospital, London. Patients presenting with acute IF are relatively rare in the UK, and their management is complex. Fleming and Remington defined IF as follows:

A reduction in the functioning gut mass below the minimal amount necessary for adequate digestion and absorption of food. ¹

Intestinal failure is caused by underlying conditions, e.g. Crohn’s disease, due to nonfunctioning absorptive surface, radiation enteritis or chronic intestinal obstruction, e.g. malignant disease; by dysmotility disorders; or by extensive removal of the small bowel, e.g. following mesenteric artery occlusion, or trauma. Recently, Lal et al reported that there are varying degrees of intestinal failure²:

• Type 1 intestinal failure—occurs following abdominal surgery and requires short-term fluid or nutritional support.

• Type 2 intestinal failure—characterised by sepsis and metabolic and complex nutritional needs, e.g. mesenteric vascular disease or a small bowel resection for Crohn’s disease. This requires resolution of sepsis before repletion of lean body mass can be achieved. A multiprofessional approach is required and reconstructive surgery may be an option in the long term.

• Type 3 intestinal failure—associated with the long-term need for PN, potentially in the home setting.

Patients who have SBS can be divided in to two groups, absorbers and secretors. In patients who are absorbers the stoma output is less than the oral intake, whereas in secretors the output is greater than the input. Absorbers tend to have more than 100 cm of small intestine and the stoma output is 2 L or less. In secretors the length of small intestine is usually less than 100 cm and the stoma output is 3 L or greater. ³ When deciding on appropriate drug therapy for short bowel it is important to know which group the patient falls into, as different drugs are more effective in either absorbers or secretors.

SBS leads to the loss of the absorptive capacity of the intestine, causing a variety of symptoms. The patient is unable to absorb water and electrolytes, leading to diarrhoea or high output from a stoma, depending on the anatomy of the patient. In severe cases the patient may become dehydrated and develop electrolyte deficiencies. The patient may also develop bacterial overgrowth, which may further worsen the diarrhoea or the output from the stoma. ⁴ The absorption of nutrients may also be affected and the patient may become malnourished and nutritional support may be required. The enteral route is the preferred route but in severe cases the parenteral route will be required. All patients are encouraged to eat and drink even if receiving parenteral nutrition, in order to maintain the integrity of the intestine and prevent hepatic cholestasis. ⁵ Enteral nutrition also prevents atrophy of the intestine and encourages the adaptation of the remaining intestine. ⁵

The dietitian and pharmacist working within this speciality aim to optimise the nutritional status of the patient, safely and effectively, taking into account the risks associated with refeeding syndrome and assisting in monitoring the metabolic and nutritional efficacy of the parenteral and enteral regimen, which can be challenging when the surgical team needs to stabilise a septic, catabolic patient. The pharmacist has an extensive knowledge of drug–nutrient interactions, PN formulation and the correction of abnormal electrolytes appropriately.

Physiology and pathophysiology

Site of the resection

In the normal human intestine most nutrients are absorbed and digested in the duodenum, jejunum and ileum with fluid being absorbed in the large bowel. The total length of small bowel from the duodeno-jejunal flexure to the ileocaecal valve has been reported to be between 275 and 850 cm. ⁶ Following a small bowel resection the ileum adapts to assume a more absorptive function. From a surgical and medical perspective loss of the ileum is more detrimental than that of the jejunum; hence surgeons will always attempt to salvage this section of small bowel if at all feasible. Intestinal transit is rapid in the jejunum, but slows down in the ileum. An ileum resection results in fast transit time, and therefore exposure and contact time between nutrients, chyme and absorptive surface area is also reduced. ⁷ Loss of more than 50 cm of terminal ileum also results in malabsorption of vitamin B ₁₂ and fat soluble vitamins. ⁷ The terminal ileum also plays an important role in absorbing bile acids; more than 90% are reabsorbed in the terminal ileum, and therefore if more than 25% of the terminal ileum has been resected, bile acids in the colon impede the absorption of sodium and water, resulting in diarrhoea. ⁷

Oxalate kidney stones

The absorption of oxalate from the gut is enhanced following jejuno-ileal bypass or jejuno-colonic anastomosis. Risk factors for oxalate stone formation include decreased urinary volume and urinary pH, hyperuricosuria, hyperoxaluria and hypocitraturia. ⁸ Normal healthy individuals only absorb a fraction of dietary oxalate; however, following restoration of continuity between the ileum and colon, patients frequently experience fat malabsorption and oxalate absorption is increased. One study reported the formation of calcium oxalate renal stones in 25% of patients with less than 200 cm of jejunum anastomosed to colon. ⁹ The restriction of dietary fat and oxalate have been demonstrated as being effective in reducing urinary oxalate excretion. ¹⁰ Calcium can precipitate with fatty acid to form soaps, hence oxalate is available for rapid absorption in the colon. Patients should be advised to avoid spinach, rhubarb, beetroot, nuts, chocolate, tea, wheat bran and strawberries. ¹⁰

Intestinal adaptation

The remaining length and type of residual bowel is only one factor in predicting the clinical and nutritional outcome of the patient. A diseased bowel, as in the case of Crohn’s disease, will have a reduced absorptive capacity. Structural and functional adaptation following a resection can occur over a two-year period in the healthy remaining bowel; however, the main adaptive process will occur in the first few months. ¹¹ An enterectomy will facilitate enhanced epithelial proliferation, and increased crypt and villous height, which is associated with dilation and elongation of the remaining intestine. Luminal nutrients have the greatest trophic effect on the adaptation process and some papers advocate the use of glutamine and short chain fatty acids; however, this has yet to be proven. ¹² The preservation of the colon may have an important role to play in adaption. This concurs with clinical experience, whereby patients with an intact section of ileum and colon demonstrate an improvement of absorption over time, whilst patients with a jejunostomy do not and are frequently dependent on PN unless access to the distal small bowel is possible.

Nutritional therapy and dietetic application

Dietetic knowledge and confidence to treat these patients can be limited; it is clear that improved postgraduate education for dietitians is required on the management of intestinal failure and HPN. ¹³ The most common queries dietitians receive from colleagues are outlined in Table 9.1.

**Table 9.1** Summary of dietetic queries received over a 12-month period
Theme	Total number of queries
Management of short bowel syndrome	37
Fistuloclysis/distal feeding and other enteral feeding in IF	25
HPN—indications and regimens	24
HPN—monitoring, vitamins + minerals (policies and protocols)	13
Management of other causes of IF	5

Assessment and monitoring of nutritional status

Assessment of nutritional status should include anthropometric measurements: weight, height, body mass index (BMI), mid-arm circumference and tricep skinfold measurements. Body weight is still the gold standard objective tool used in nutritional assessment, as it is simple and calibrated scales are readily available. Caution is required in patients with high output stomas resulting in precarious fluid balance as rapid fluctuations in weight are likely to reflect changes in hydration, rather than lean body mass. Weight is often expressed as an index of height to give a measure of body mass index (BMI), where a BMI of 20–25 kg/m ² is considered desirable. A BMI of < 18.5 kg/m ² is used to define undernutrition. ¹⁴ It is generally accepted that a loss of body weight greater than 10% in the preceding 3 months (and non-intentional) is considered significant in terms of clinical outcome and that 20% recent weight loss is evidence of protein energy malnutrition. ^15,¹⁶ Patients should be weighed on admission and on a weekly basis. ¹⁷ Some patients present with psychological issues due to altered body image related to rapid weight loss as a consequence of malabsorption and loss of functional status which has a negative impact on quality of life. By measuring weight and mid-arm anthropometry it can provide a baseline and subsequent measure of improvement in nutritional status for the patient. ¹⁸ Measurement of upper arm anthropometry by the same dietitian in order to avoid interobserver error can be compared to standardized tables but consideration must be given to the demographics of the original populations recruited to compile the reference tables, the sample size and whether these reference tables apply to a the patient population. ^19.^20.^{and 21.}

Biochemical monitoring of serum and urinary electrolytes provide an essential adjunct when assessing fluid balance and the efficacy of the nutrition support. Regular monitoring of patients receiving PN is essential to ensure safe and effective nutritional therapy. Monitoring must include clinical, nutritional and biochemical parameters. The information in Table 9.2 can to be used as a guide but each practitioner should follow local practice guidelines.

**Table 9.2** Summary of biochemical monitoring ²²
Parameter	Frequency	Notes
Sodium	Daily Once stable twice weekly, then weekly	• Increased sodium: usually dehydration, rarely sodium excess. Often associated with increased urea. Check fluid balance and consider increased fluid input • Decreased sodium: usually fluid overload rather than depletion. Check for losses. Check fluid balance and consider decreased fluid input
Potassium	Daily Once stable twice weekly, then weekly	• Increased potassium: consider sample haemolysis, lipaemia or contaminated sample • Decreased potassium: check for increased gastrointestinal losses Check for hypomagnesaemia if resistant to treatment
Urea	Daily Once stable twice weekly, then weekly	• Increased urea: occurs in renal failure, suggestive of dehydration Consider increased fluid input • Decreased urea: suggestive of fluid overload or poor nutritional status. Consider decreased fluid input
Creatinine	Daily Once stable twice weekly, then weekly	• Elevated in renal failure
Phosphate	Daily Once stable twice weekly, then weekly	• Increased phosphate: occurs in renal failure • Decreased phosphate: may be a result of refeeding syndrome or existing alcohol abuse
Calcium	Daily Once stable twice weekly, then weekly	• Increased calcium: occurs in renal failure • Decreased calcium: may be result of refeeding syndrome or phosphate supplementation
Magnesium	Daily Once stable twice weekly, then weekly	• Increased magnesium: occurs in renal failure • Decreased magnesium: may be result of refeeding syndrome or existing alcohol abuse. May get hypomagnesium from increased GI losses
Glucose	Three to four times daily until stable, then daily, then weekly	• Elevated glucose: may need to start insulin • Hypoglycaemia: may occur in PN if stopped abruptly. Consider reducing rate of PN over last 1–2 hours
Liver function tests	Twice weekly, then monthly when stable	• May be elevated as a result of underlying or pre-existing hepatic disease, drug therapy, sepsis, long-term PN, overfeeding • Treat accordingly
Albumin	Twice weekly, then monthly when stable	• Poor marker of nutritional status. An indicator of the severity of disease • Treat appropriately
FBC, PT	Weekly, then monthly	• Low Hb result may be associated with lack of iron in PN • WCC rises in infection
Triglycerides	Weekly, then three monthly	• If elevated review fat intake
Trace elements	Monthly	• Long-term PN patients only • Treat appropriately
Zinc	Monthly	• Characteristic rash occurs in deficiency, often associated with poor wound healing. Increased loss in fistula/diarrhoea
Urinary electrolytes	Weekly, then monthly	• Urinary sodium is particularly useful in patients with complex fluid balance

Changes in nutritional status often occur because of non-nutritional factors. Failure to improve nutritional status may be due to sepsis/acute disease state, rather than the inadequate provision of nutrition. Monitoring and noting the trend view of markers of the inflammatory response, such as C-reactive protein (CRP), white blood cell count (WCC) and platelets, are useful in indicating sepsis and when the patient is entering the anabolic phase. Albumin levels are considered to reflect disease severity rather than nutritional status, as levels can fall following surgery, with inflammatory markers, and can be normal in cases of severe malnutrition, such as anorexia nervosa. ^23.^24.^{and 25.} However, albumin may be a predictive factor for anastomic leak; it is common practice that surgeons will aim for a patient’s albumin to be within the normal range prior to reconstructive surgery. ²⁶

Long-term provision of PN is associated with hepatobiliary complications from mild elevation of LFTs to hepatic steatosis and intrahepatic cholestasis. ²⁷ By actively encouraging oral diet this results in the stimulation of biliary and chyme secretions. Therefore oral intake should be encouraged, unless it is contraindicated, e.g. bowel perforation with intra-abdominal cavities, abscesses, or fistula. Lumen and Shaffer reported an inverse relationship between raised alkaline phosphatase and remaining length of small bowel, especially patients with < 100 cm of small bowel. ²⁷

Most patients with SBS can be managed by oral enteral nutrition and may require PN, depending on the absorptive capacity of the remaining bowel (Table 9.3).

**Table 9.3** Summary of clinical and anthropometric monitoring ²⁸
Parameter	Frequency	Notes
Clinical condition of patient	Minimum of daily	• Observe closely for changes, e.g. pyrexia, vomiting, diarrhoea, increased gastrointestinal losses. Inform senior clinician if necessary
Weight	Weekly	• Plot on weight chart • Inform consultant/nutrition team if weight decreases over 2 or more weeks
Height	On admission	• Record in notes
Mid-arm muscle circumference	Monthly	• Record in notes
Temperature	Daily	• Pyrexia could be associated with catheter-related sepsis. Patient requires urgent review by clinician
Fluid balance	Daily	• Record fluid input/output over 24 hours to indicate fluid overload/dehydration
Total energy intake	Daily	• Calculate PN administered versus PN prescribed. Inform PN pharmacist if less than 90% administered • For patients receiving a combination of PN with enteral nutrition or food, ensure an accurate record of intake is maintained and reviewed twice weekly
Catheter entry site	Daily	• Follow local practice when handling catheter • Inform clinician if any problems, e.g. phlebitis, extravasation observed
Cardiac monitoring	Continuous	• Consider for patients receiving PN with potassium concentration in excess of 40 mmol/L

Eating is associated with many cultural, behavioural, social and psychological factors as well as a means of providing the body with macro- and micronutrients. Patients may have experienced many adverse side effects of malabsorption, e.g. abdominal pain, cramps and diarrhoea, and may be apprehensive to eat.

Short bowel—end jejunostomy

In this group of patients the main challenge is achieving electrolyte and fluid balance. Additional sodium may need to be added to the diet at an optimal concentration of 120 mmol/L or consumed as oral rehydration solution, although compliance with the rehydration solutions can be an issue due to limited palatability. ²⁹ Patients should be educated to:

• Recognise the symptoms of dehydration: dizziness, thirst and reduced/concentrated urine;

• Restrict hypotonic fluids, e.g. water, tea, coffee, squash to 1000–1500 mL/day;

• Take additional fluids as an oral glucose-electrolyte rehydration solution, with a sodium content > 90 mmol/L, as outlined below; ³⁰ and

• Take medications to reduce stoma losses in relation to meal times.

Nutritional requirements for fluid, electrolytes and nutrients are not likely to change over time, which is in contrast to patients with a colon in continuity with small bowel. ³¹

Oral rehydration mixtures

These mixtures contain water, electrolytes and glucose to aid the active transport of sodium. Care must be taken to ensure that hypotonic solutions are not used as this will increase the gastrointestinal output. ³² The patient may also develop bacterial overgrowth, which may further worsen the diarrhoea or the output from the stoma. ³² Patients with a stoma output of greater than 1200 mL may gain benefit from sipping up to a litre of these solutions throughout the day. There are a number of different solutions available for use but they must contain at least 90 mmol/L to prevent sodium loss in the gut. Concentrations of greater that 90 mmol/L of sodium may aid sodium absorption. ³² There are a number of measures which can be instituted to increase the palatability of the solutions such as adding flavourings and keeping the solution chilled. There is evidence that swapping the sodium bicarbonate for sodium citrate or using glucose polymers in the solution may further increase palatability of the solutions. ³³

Pharmacological treatments for short bowel syndrome

There are a number of pharmacological treatments which may be used to reduce stoma/fistula output in patients with SBS. ³² In many cases a combination of agents will be used to control the output. If these agents are used correctly it may prevent a patient requiring long-term parenteral support. ³² The choice of pharmacological agent used to reduce the diarrhoea or the output from the stoma will depend on the length and type of bowel remaining. The most common classes of drug used are the antimotility and antisecretory agents.

If the patient has any coexisting diseases the drug therapy should be reviewed as the absorption of drugs may be reduced. The dose may need to be increased or syrup used to increase the surface area to improve the absorption. In some cases a different route may need to be employed to ensure effective therapy, e.g. topical patches for hormone replacement therapy, or pain control. ³⁴ It is common practice to administer antibiotics parenterally to ensure the minimum inhibitory concentration is achieved.