Gastric tonometry and intramucosal pH - Theoretical principles and clinical application

Gastric or intestinal luminal tonometry is a method for monitoring critical ly ill patients. It offers an index of the adequacy of aerobic metabolism i n a tissue that is particularly sensitive to alterations in its perfusion s urd oxygenation: the gut mucosa. It is based on the measuring the increase in tissue CO2 production that accompanies anaerobic metabolism. The method simply consists of a balloon in the stomach, which measures intramucosal pC O(2). From this measurement and from the arterial bicarbonate concentration gastric intramucosal pH (pHi) can be calculated, assuming that bicarbonate concentration in the gastric mucosal tissue is in equilibrium with systemi c arterial bicarbonate. Despite possible clinical benefit from the measurem ent and the therapy of low pHi values in critically ill patients, the theor etical, experimental and pathophysiological implications for the monitoring of intramucosal acidosis in the gut are not yet fully understood. There ar e still some open methodological questions crucial for further clinical int erpretation.