Gastric Tonometry

Abstract

Because tissue hypoxia plays a major role in the morbidity and mortality of critically ill patients, achieving adequate tissue oxygenation is considered the main goal in the intensive care unit during initial management of patients with shock, severe sepsis, trauma, and the multiorgan dysfunction syndrome. Unfortunately, systemic parameters of tissue oxygenation are not reliable enough to represent “true” tissue oxygenation status. Methods developed to monitor oxygen tissue metabolism, such as phos-phorus-31 nuclear magnetic resonance, near-infrared spectroscopy, and tissue Po2 electrodes are still far from clinical application. A new approach to this problem is the measurement of gastric intramucosal pH (pHi) with a gastric tonometer. This device consists of a modified nasogastric tube attached to a silicone balloon that is filled with saline. After an equilibration period, saline solution can be sampled and its Pco2 measured in a blood-gas analyzer. Arterial bicarbonate is simultaneously measured. Gastric pHi is then easily calculated using the Henderson-Hasselbalch equation. Its value has been experimentally validated, comparing it with direct electrode tissue pH measurements. A growing body of evidence supports its clinical value at the present time. Several clinical investigations show that pHi is a sensitive and specific prognostic marker. Gastric pHi behavior is able to predict multiorgan dysfunction and mortality in different groups of critically ill patients. Its use to guide resuscitation maneuvers could contribute to mortality reduction. From the few years of basic and clinical research in which this technique has been used, it appears to be a useful tool to assess tissue oxygenation status.