[Intramucosal pCO2 measurement as gastrointestinal monitoring]

The improvement of tissue perfusion by alterations in global parameters has led to the concept of supranormal oxygen delivery. However, this approach did not cause a significant reduction in the mortality of critical illness. As a consequence, recent research activity concentrates on regional monitoring and on the therapy of especially vulnerable, injury-prone organ systems. Gastric tonometry, a monitoring device of the gastrointestinal region that has produced promising results, can be considered as an area of special attention. The intramucosal pCO2 (piCO2) and the calculated intramucosal pH (pHi) of gastric tonometry can indicate an impairment of the gastrointestinal perfusion and thus point to an immanent injury of the barrier function of the gut mucosa. In clinical practice, however, apart from several technical problems with conventional, discontinuous gastric tonometry, some misconceptions exist in respect of the interpretation of derived pHi data. The technical problems can be overcome by a new fibreoptic piCO2 measurement, an automatic and continuous technique. The analysis of the obtained data must take the physiology of the CO2- and HCO3(-)-metabolism into account. Coupling of the locally derived piCO2 with systemic arterial HCO3- concentration that results in the pHi as the sensitive parameter of the gastrointestinal malperfusion as suggested by Fiddian Green, is not correct. Taking respiratory pCO2 changes into consideration, only the PiCO2 can detect gastrointestinal malperfusion. Therefore, the rather confusing terms "gastric tonometry" and "pHi measurement" should be avoided and the new monitoring technique be defined as "intramucosal pCO2 measurement". Continuous piCO2-measurement is a monitoring technique with high sensitivity in detecting gastrointestinal hypoperfusion based on an intramucosal CO2 accumulation. The clinical significance of the primary parameter piCO2 as well as the suitability of this technique as a monitoring tool for the daily routine must be re-assessed.