Gut intramucosal pH and intraluminal PO2 in a porcine model of peritonitis or haemorrhage.

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Abstract
The tonometric method of detecting decreased gut intramucosal pH (pHi) is based on the fact that carbon dioxide can diffuse through the wall of the silastic balloon of the tonometer. By using deoxified saline and measuring PO2 as well as PCO2 this study aimed to follow changes in mucosal PO2 and relate them to changes in pHi in peritonitis versus haemorrhage. Twenty five pigs were used. Five were controls, in 10 peritonitis was induced by the instillation of faeces in the abdominal cavity, and 10 were bled, half of them stepwise during three hours, and half of them rapidly down to a mean (SEM) arterial pressure of 30 (10) mm Hg. The drop in pHi correlated well with decreasing intraluminal PO2 (r = 0.63 (0.13)) in haemorrhage. In peritonitis this drop occurred within a very limited change in intraluminal PO2 (r = 0.06 (0.17)). Thus oxygen seemed to be present in the mucosa at the same time as there were signs of anaerobic metabolism as evidenced by a low intramucosal pH. Impaired oxygen extraction or utilisation, or both, is proposed as an explanation to this seemingly paradoxical situation.