Gastric tonometry: a new monitoring modality in the intensive care unit

In many critically ill patients, systemic measures of hemodynamic and O2 transport variables may not be sufficiently sensitive to portray the complex interaction between energy requirements and energy supply in all tissues. Gastric or intestinal tonometry has been proposed as a relative noninvasive index of the adequacy of aerobic metabolism in the gut mucosa, a tissue that is particularly vulnerable to alterations in perfusion and oxygenation. The gut mucosa lacks some of the microvascular control mechanisms that allow other tissues, such as the heart, skeletal muscle, and the brain, to increase tissue perfusion during times of stress, and, just like the canary, it will display metabolic changes indicative of dysoxia earlier than those more "vital" tissues. The tonometric measurement of mucosal PCO2 rests on the premise that equilibrium exists between mucosal and luminal PCO2. Increases in mucosal PCO2, or conversely, decreases in mucosal pH (pHi), are associated with the development of intestinal mucosa ischemia. The clinical utility of pHi to detect intestinal mucosal ischemia has been demonstrated in patients undergoing abdominal aortic surgery. Further, a low gastric mucosal pHi on admission to the ICU appears to be predictive of mortality and pHi-guided resuscitation may improve outcome in a subpopulation of patients admitted to the ICU with normal pHi, perhaps by preventing splanchnic ischemia and the development of a systemic oxygen deficit.