Q: How to rule out Osmotic Diarrhea in ICU?


Answer: The easiest way to rule out osmotic diarrhea is via calculating simple formula of Osmotic gap

290-2 x (stool Na + Stool K)

Gap more than 100 mOsm/kg, is probably an osmotic diarrhea. 
Gap less than 50mOsm/Kg rules out osmotic diarrhea. 
Gap between 50 and 100 mOsm/kg is equivocal

In ICU most usual causes of osmoticc diarrhea are medications (containing nonabsorbable sugar alcohols like Sorbitol) and tube feeds.


Further reading: -  Here -Mechanisms, prevention, and management of diarrhea in enteral nutrition -  Kevin Whelan and Ste´phane M. Schneider -  Current Opinion in Gastroenterology 2011, 27:152–159