Short bowel syndrome: Clinical sciences

Short bowel syndrome is characterized by the insufficient length or function of the small intestines, resulting in malabsorption of water, electrolytes, as well as micro and macronutrients. It’s most commonly caused by extensive surgical resection of the small intestine due to trauma, inflammatory bowel disease, or congenital abnormality. Usually, patients with less than 200 cm of small bowel are at risk for developing short bowel syndrome as the decrease in absorptive surface area and shorter transit times through the gastrointestinal tract can impair the absorption of gastrointestinal contents. Consequently, patients can present acutely with volume depletion, or with metabolic abnormalities and weight loss from chronic intestinal failure. Management of short bowel syndrome requires multidisciplinary care, including nutritional support, medical management, and in some cases, surgery.

When a patient presents with a chief complaint suggestive of short bowel syndrome, the first step is to perform an ABCDE assessment to determine whether the patient is unstable or stable. If the patient is unstable, begin acute management by first stabilizing the airway, breathing and circulation. Then, establish IV access and administer fluids while monitoring vital signs like heart rate, blood pressure and oxygen saturation.

Next, perform a focused history and physical examination, and obtain labs including a complete blood count, comprehensive metabolic panel, and serum lactate to assess for dehydration and electrolyte abnormalities.

Typically, patients will have a history of extensive bowel resection. In adults, the most common reasons for bowel resection are inflammatory bowel disease, mesenteric ischemia, radiation enteritis, or trauma. Patients might present with severe diarrhea or high stoma output, if they have one. Keep in mind, high stoma output is defined as more than 1.2 liters per day. Additionally, they might report significant weight loss, decreased or absent urine output, lethargy, weakness, or altered mental status.

On physical exam, you might find tachycardia and hypotension as well as dry mucous membranes and decreased skin turgor, which are all signs of acute dehydration. If the patient has a stoma, make sure to examine the stoma and the contents of the ostomy bag, which might show watery stoma output.

Now, labs can show a variety of abnormalities. The complete blood count can be normal, or show anemia or elevations in multiple cell lines due to hemoconcentration. The comprehensive metabolic panel will often reveal electrolyte abnormalities, like hypokalemia; an elevated BUN to creatinine ratio; and elevated serum creatinine. In addition, you can expect serum lactate to be elevated. If these are your findings, you can diagnose your patient with short bowel syndrome with acute volume depletion.

The management for an unstable patient with short bowel syndrome and acute volume depletion begins with supportive care. This includes IV fluid resuscitation and strict monitoring of intake and output. Make sure to start intravenous electrolytes and micronutrient replacement as soon as possible. You can also initiate antisecretory medications, like proton pump inhibitors, and antidiarrheal medications, such as loperamide. Once the patient is stabilized, remember to check for other nutritional insufficiencies.

Alright, now that the unstable patients are taken care of, let’s go back and talk about stable ones. For stable patients, your first step is to perform a focused history and physical examination. You should also order a complete set of labs including CBC, CMP, prealbumin, magnesium, vitamin B12, Vitamins A, D, E, and K, iron, folate, zinc, citrulline, and fecal fat testing. These labs test for the patient’s nutritional status.

Similar to unstable patients, stable patients will also have a history of extensive bowel resection, chronic diarrhea, high stoma output if they have one, as well as significant weight loss, and fatigue. On physical exam, patients can be underweight, have a low BMI, and muscle wasting, which are signs of chronic undernutrition. You might also see watery stoma output, peripheral edema, peripheral neuropathy, bruising, or rash, all signs of malnutrition and vitamin deficiency.

Now labs might reveal microcytic anemia from iron deficiency, or macrocytic anemia due to folate or vitamin B12 deficiency. You can also expect to find one or more electrolyte abnormalities including hypokalemia, hypocalcemia, hypophosphatemia, hypomagnesemia; as well as abnormal vitamins and nutritional levels, such as low vitamin B12 and fat-soluble vitamins A, D, E, and K, as well as low folate and zinc. Additionally, these patients typically have low citrulline, which is an amino-acid produced by enterocytes in the small intestine. Lastly, fecal fat testing might be positive, indicating malabsorption of fat in the small intestine. Here’s a clinical pearl! The type and severity of electrolyte and nutrient deficiencies in patients with small bowel syndrome will vary depending on which portion of the bowel was resected and how much bowel remains. For example, vitamin B12 deficiency and bile acid-induced diarrhea are common after resection of the terminal ileum. Patients with end ileostomy typically have more severe deficiencies than patients with anastomosis of the ileum to the colon.

Alright, if these features are present, you can diagnose the patient with short bowel syndrome with chronic intestinal failure. In general, intestinal failure means that bowel function is below the minimum required for adequate hydration and nutrition. So, these patients often need parenteral supplementation.