[Monitoring by measurement of gastrointestinal mucosal pH value (pHi)]

Noninvasive measurement of mucosal pH by tonometry provides information on the adequacy of gastrointestinal mucosal oxygenation. The technique requires tonometer catheters (commercially available from Tonometrics) and a standard blood gas analyzer. After positioning of the catheter in the stomach or gut for at least 30 min, fluid is withdrawn from the prefilled balloon mounted on the catheter tip for pHi measurements. The pCO2 in the withdrawn fluid and bicarbonate concentration in the arterial blood are determined and pHi is calculated according to the Henderson-Hasselbalch equation. The tonometer technique has been validated in experimental studies and pHi has been shown to be a useful parameter to estimate adequacy of oxygenation of the mucosa surrounding the tonometer balloon. In surgical patients, pHi was found to be of high predictive value concerning incidence of complications; return of pHi towards higher values was found to be associated with a higher survival rate. In intensive care units, pHi-guided resuscitation proved to be superior to conventional therapy. Tonometric measurement of pHi is a useful parameter to monitor mucosal oxygenation and to provide information on the probability of complications and patient outcome. Further studies are needed in well-stratified patient groups with a present lower limit of pHi, triggering defined therapeutic interventions to improve mucosal oxygenation.