Wednesday January 10, 2007
Stool Osmolal Gap !


About one third of patients on enteral feeding develops diarrhea in ICU. One easy way to confirm diarrhea secondary to enteral feed is to calculate Stool Osmolal Gap. The formula of Stool Osmolal Gap is

Stool Osmolal Gap = Measured stool osmolality - 2 (stool Na - stool K)

A stool Osmolal Gap more than 160 mOsm/kg H2O is most probably related to enteral feed in ICU or may be due to medications. Other causes of higher stool osmolal gap are pancreatic insufficiency, celiac sprue, lactose intolerance etc. but they are relatively uncommon.


Note: In ICU if stool osmolal gap is less than 50 mOsm/kg H2O, secretory diarrhea from C.diff. colitis should be ruled out as a first thing.