Non-invasive monitoring of the gastrointestinal mucosal perfusion has been shown to be useful as a predictor of outcome in many clinical settings including cardiac surgery. Tonometry is a non-invasive and reliable, though indirect method of splanchnic oxygenation monitoring.It has been confirmed that a decrease in pHim below 7.35 signifies a critical level of ischemia in the visceral vascular bed and is well correlated with a number of serious complications after major cardiac procedures.