Challenges to intestinal pO₂ measurement using EPR

Acute and chronic intestinal ischemia has been linked to the development of gastrointestinal symptoms such as abdominal pain, nausea and vomiting, bowel dysfunction and more seriously, the complications of sepsis, shock and death. Advances in electron paramagnetic resonance (EPR) oximetry have resulted in accurate and reliable in vivo measurement of the partial pressure of oxygen (pO(2)) in solid organs (e.g., muscle, heart) [1], but has yet to be tested in thin walled organs such as intestine. Our ultimate goal is to noninvasively monitor intestinal pO(2) during acute and chronic intestinal ischemia in a rat model. A series of experiments to deliver oxygen-sensitive indicator probes to the small/large intestine by intravenous, luminal and wall injection, as well as direct placement of a solid probe against the outer intestinal wall were attempted. Only the LiNc:BuO:PDMS chip sutured to the peritoneal wall and in direct contact with the intestine allowed for noninvasive pO(2) measurement by EPR. However, the validity of site-specific intestinal pO(2) measurement could not be confirmed and the obtained pO(2) value likely reflected peritoneal cavity oxygenation. Developing methods for probe placement on or inside the intestinal wall are needed for noninvasive, site-specific intestinal pO(2) measurement by EPR to track changes during acute and chronic intestinal ischemia.