Discussing the use of bile salt-binding resins, such as colestyramine (cholestyramine USAN), and somatostatin peptide drugs, such as octreotide, for the treatment of diarrhoea we saw that these drugs are only used for specific types of diarrhoea, such as secretory diarrhoeas. One example given was diarrhoea following vagotomy.

But why does vagotomy cause diarrhoea? Vagotomy is a surgical technique indicated for patients who develop acute complications from peptic ulcer disease or chronic symptoms despite being on maximally tolerated medical therapies. Damage to the vagus nerve can also occur following bariatric surgery, fundoplication, and oesophagal resection.  Postvagotomy diarrhoea has been described in up to 30 percent of patients. Many patients have transient watery diarrhoea for three to six months postvagotomy but in some the diarrhoea can be severe and chronic.

One might think that vagotomy should cause constipation, not diarrhoea, since cutting the vagus nerve decreases parasympathetic innervation of the gastrointestinal tract and the “rest and digest” functions of the parasympathetic nervous system promote gastrointestinal secretions and motility.

However, vagotomy often also damages branches of the vagus nerve innervating the liver and gallbladder. This leads to gallbladder distension and secretion of excess bile salts. This triggers diarrhoea. The fact that colestyramine can control postvagotomy diarrhoea supports the hypothesis that excess bile salts in the intestine are involved in stimulating colonic secretions and causing the diarrhoea.

Additionally, some patients with vagotomy develop gastric retention and require an additional drainage procedure several months after the initial operation.  This can lead to gastric dumping of hyperosmolar gastric contents into the small bowel within 30 minutes of a meal. This triggers an influx of water into the lumen resulting diarrhoea. The acute reduction in plasma volume due to the rapid influx of water into the bowel can also trigger diaphoresis, dizziness, hypotension, tachycardia, and headache.

Reference:

Perez, A. Vagotomy. Soybel, D., Lamont, JY, Chen W, ed. UpToDate. Waltham, MA: UpToDate Inc. http://www.uptodate.com (Accessed on November 29, 2017).