An assessment of tonometry and regional splanchnic blood flow during aortic cross-clamping in the pig.

We aimed to evaluate the tonometer in the assessment of gastrointestinal ischaemia induced by an infrarenal aortic cross-clamp. Nine anaesthetized pigs were cannulated for haemodynamic monitoring and radionuclide labelled microsphere (RLM) injection. Gastric and sigmoid tonometers were positioned. After haemodynamic stabilization an infrarenal aortic cross-clamp was applied. Animals were sacrificed at the completion of the study and tissue sampled from the stomach and sigmoid colon for regional blood flow measurements. Measurements were made pre-clamp, post-clamp, pre-release and post-release. Haemodynamic parameters, gastric intramucosal pH (pHi) and blood flow did not change throughout the experiment. Arterial pH increased during cross-clamp and returned to baseline post-release. Arterial bicarbonate fell post release. Sigmoid blood flow fell during cross-clamp. The sigmoid pHi fall, delayed until pre-release, remained low post-release. Although there was a consistent fall in sigmoid pHi, 63% of post-clamp values remained within the baseline range. We conclude that maintaining haemodynamic parameters around baseline values resulted in maintenance of gastric mucosal perfusion as indicated by a steady gastric pHi. However, below the aortic cross-clamp, delay between change in sigmoid colon blood flow and change in pHi and wide variation in sigmoid pHi limits the value of an individual pHi measurement in detecting ischaemia.