A noninvasive method for monitoring intestinal ischemia: changes in the pulmonary clearance of helium instilled into the colon as an index of colonic blood flow

Abstract

To evaluate the concept that changes in colonic blood flow will predictably alter the absorption of colonic gas, we measured the pulmonary clearance rate of helium (CHe) which was instilled rectally into the colon of rabbits at a dose of 2 ml/kg. CHE reached a plateau after 20 min at 109 nmol/min/kg. Using hypoxemia as a cause for bowel ischemia, at PAO2 = 38 torr, we noted a marked decreased in CHe from 110 nmol/min/kg to 75 nmol/min/kg (p less than 0.025). Because helium absorption from the colon is diffusion limited, a model can be developed relating "subvillus" colonic blood flow to pulmonary helium clearance. From this model we would predict the hypoxemia induced change in CHe to be secondary to colonic hypoperfusion. This type of indirect monitoring could be useful in detecting patients with bowel ischemia.