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Background and aims: Unrecognized intestinal mucosal ischemia in severely ill patients may trigger development of multiple organ failure. Such ischemia can be evaluated by intraluminal tonometry reflecting mucosal PCO₂ and intramucosal pH (pH_i). The aims were to develop an apparatus for continuous saline tonometry (CST), to analyse circulatory control mechanisms during intestinal hypoperfusion and to evaluate the effect of dopexamine on intestinal circulation.

Methods: A modified standard tonometry catheter was integrated in a closed system with circulating saline. By measuring saline PCO₂ in a measurement unit pH_i could be calculated. This novel system was tested in vitro and in vivo. In a porcine study, CST was evaluated against standard saline tonometry, tissue oxygenation (PO_{2 TISSUE}), jejunal mucosal perfusion (laser doppler flowmetry; LDF) and mesenteric net lactate flux during graded reductions of superior mesenteric arterial pressure (P_SMA). Local control mechanisms for maintenance of intestinal oxygenation were analysed. Effects of dopexamine on the intestinal vascular bed were explored. Mucosal lactate production was assessed by microdialysis.

Results: CST measured accurate PCO₂ values and changes in pH_i during restricted intestinal circulation and at reperfusion. Local control mechanisms were insufficient at a P_SMA of 30 mmHg, pH_i was reduced to 7.10 and intestinal net lactate production was demonstrated. Absence of anaerobic intestinal metabolism was verified at P_SMA ≥ 50 mmHg, pH_i ≥ 7.22 and a PCO₂ gap ≤ 15.8 mmHg. Dopexamine induced negative regional metabolic effects at the lowest P_SMA, as expressed by decreased PO_{2 TISSUE} and pH_i, increased PCO₂ gap and intestinal net lactate production.

Conclusions: CST reflected changes in pH_i, induced by intestinal hypoperfusion and at reperfusion. Levels of P_SMA, pH_i and PCO₂ gap as indicators of aerobic conditions were defined. Dopexamine induced a decrease of PO_{2 TISSUE} and pH_i as well as an increase in lactate flux at the lowest P_SMA level.