Short Bowel Syndrome (SBS) is a condition in which the body cannot properly absorb nutrients because part of the small intestine is missing. Adults have 480cm of small intestine divided into duodenum, jeunum and ileum. The last part of the ileum connects with the colon through a valve called ileo-cecal valve and its function is to prevent the backflow of contents from the colon to the small intestine.
When the small intestine measures 180cm there is a risk of developing SBS, but at 60cm or less, regardless of the presence of the colon, the patient becomes dependant on parenteral nutrition (non-oral intake) since there is not enough intestine to allow minimum digestion and absorption. This state is also known as intestinal failure.
What are the causes of SBS in adults?
Surgical resection of small bowel:
Obstruction (thrombosis or embolism) of the mesenteric arteries that supply blood to the intestines. This leads to gangrene (dead tissue) and emergency resection.
Crohn’s disease causing repeated and multiple resection of small bowel.
Strangulated large hernias.
Inflammation of the intestines secondary to radiation therapy (radiation enteritis).
What are the common symptoms?
In general, each part of the intestines has a specific role absorbing specific nutrients, vitamins and minerals. Some implications of the disease will depend upon the part of the intestines that have been removed. The most common and general symptoms of SBS are diarrhea with large amounts of fat, weight loss, abdominal pain, gas, bloating, fatigue and weakness.
There may be other symptoms related to a specific vitamin or mineral deficiency: Dermatitis (fatty acids), inflammation in the mouth and tongue (niacin, riboflavin), neurological problems (Vitamin E), pallor and weakness (iron deficiency) among many others.
Implication of the site of intestinal resection:
The symptoms associated with bowel resection are highly dependent upon the physiology of the remaining small bowel, since each bowel segment has unique characteristics for absorption. Once a segment is removed, the remaining intestine will compensate the absence of the other, a process called “adaptation,” that usually lasts up to a year. Most of this intestinal adaptation occurs in the ileum.
The ileum is capable of undergoing marked adaptation by an increase in the villus surface area (increase the size of the lining), increase intestinal length, diameter and motor function. All these structural changes lead to an enhancement of nutrient uptake in the remaining segment of the bowel.
The consequences of the resection of specific parts of the intestines:
Here is where most nutrients (lipids, carbohydrates, proteins, vitamins and minerals) are absorbed. A marked reduction in their absorption is seen with very modest adaptative changes, though with time some will occur to compensate for its loss.
Here is where Vitamin B12, bile acids and fluids are absorbed. The ileum also regulates the speed of the intestine by slowing down gastric emptying to facilitate absorption of nutrients in the small bowel, a process called “ileal brake,” mediated by hormones secreted by its cells. Finally, loss of the valve that connects the terminal ileum with the colon (ileo-cecal valve) will be associated with a reduction in the intestinal time which impairs nutrient absorption, as well as loss of the barrier that prevents colonic material to reflux back into the ileum. This leads to an increase in bacterial population in the small bowel which causes malabsorption as well.
Here is where water, electrolytes and short chain fatty acids are absorbed, as well as up to 15% of energy requirements, primarily from fermented carbohydrates. This colonic property is used in patients in whom a large small bowel resection was done with a normal remnant colon. By increasing carbohydrates, the colon is capable of increasing absorption from 15 – 50% of energy requirements. This provides a great compensatory mechanism, a good example also of “adaptation.” For the above reasons, patients are more likely to tolerate small bowel resection when they have an intact colon.
How is SBS treated?
Once SBS is suspected in a patient, treatment begins as soon as possible. The likelihood of a successful transition from parenteral (venous infusion, also called total parenteral nutrition or TPN) to enteral (oral formulas or elemental food) feeding will depend upon the length and the segment of small bowel left, the presence or not of the colon and the ileo-cecal valve and at last the intestinal adaptation of the remaining bowel.
The process called “intestinal rehabilitation” refers to the multidisciplinary approach aimed at improving intestinal function and the decrease of parenteral nutrition dependency in a patient. This approach is nutritional, pharmacological and sometimes surgical. The goal is not only to free the patient from parenteral nutrition, but also avoid intestinal transplantation. No treatment is successful without patient education and understanding of the disease; this allows them to participate in their management plan as well as their close family members. It also allows them to set realistic expectations in terms of dietary modifications which are necessary to maximize nutritional benefits, minimize symptoms and avoid nutrient deficiencies.
1. Enteral feeding:
Should be introduced as soon as possible to promote intestinal adaptation since it stimulates release of digestive juices, hormonal secretions and maintains the integrity of the gut barrier and its inmmunoregulatory mechanisms. The goal is to taper parenteral nutrition and slowly start oral feedings. Initially, an elemental diet in continuous fashion increases absorption of lipids, proteins and net energy. Later on, a complex diet also in a continuous fashion promotes and facilitates intestinal adaptation thereby accelerating progression to oral feedings. Bolus feeding should be introduced slowly and progressively. Patients tend to tolerate complex carbohydrates much better than simple ones as well as fatty food. Ideally, nutrition should be frequent (every 2- 3 hours), balanced with proteins, carbohydrates, with lipids (40% at least) and without hypertonic beverages (sodas or juices) or high carbohydrate feedings.
3. Antidiarrheals: loperamide, codeine and diphenoxylate.
4. Antisecretory Agents: ranitidine, omeprazol (decrease acid) or octreotide (reduces fluid loss and slows transit, but slows adaptation process).
5. Antibiotics: decrease bacterial overgrowth that contributes to diarrhea and decrease nutrient absorption (ciprofloxacin, metronidazol or rifaximin).
6. Bile Sequestrants: agents that decrease diarrhea (cholestyramine). E. Growth Factors: agents that promote and enhance adaptation beyond normal limits, increasing intestinal absorptive capacity and decreasing the need for parenteral nutrition support.
E.1 Glucagon like peptide-2 (GLP-2): Teduglutide (GattexR), approved by the FDA recently for the treatment of SBS.
E.2 Glutamine and Growth Hormone (experimental).
F. Supplementation: vitamins such as B12, A, D, E, K and minerals, potassium, chloride, magnesium, calcium, zinc, iron and selenium.
Refers to specific types of surgical intervention that can contribute to the enhancement of the absorptive surface area and/or decrease in intestinal transient time. Some of them are:
1. In case of intestinal obstructions: lyses of adhesions. B. Reversal of an ostomy (colostomy or ileostomy).
2. Restoration of intestinal continuity.
3. Small bowel transplantation:
Only reserved for patients with SBS who are not candidates for parenteral nutrition that have developed complications from it. It is done only in highly specialized centers across the country.
What are the complications of SBS in adults?
If none of the treatments or options explained before work in a patient, the consequences of SMB are in a short term and can include dehydration, and electrolyte imbalances (loss of potassium, calcium and magnesium), as well as disequilibrium of the pH of the body (alkalosis or acidosis).
For mid and long term, osteoporosis due to calcium and Vitamin D malabsorption, kidney stones, increase of acid production in the stomach and decrease in gastric time leads to ulcers formation.
Online information for patients:
The Oley Foundation: www.oley.org
American Society for parenteral and Enteral Nutrition: www.nutritioncare.org
Short Bowel Syndrome Foundation: www.shortbowelfoundation.org
Short Bowel Support: www.shortbowelsupport.com