Tissue capnometry: Does the answer lie under the tongue?

Abstract

Increases in tissue partial pressure of carbon dioxide (PCO2) can reflect an abnormal oxygen supply to the cells, so that monitoring tissue PCO2 may help identify circulatory abnormalities and guide their correction. Gastric tonometry aims at monitoring regional PCO2 in the stomach, an easily accessible organ that becomes ischemic quite early when the circulatory status is jeopardized. Despite substantial initial enthusiasm, this technique has never been widely implemented due to various technical problems and artifacts during measurement. Experimental studies have suggested that sublingual PCO2 (PslCO2) is a reliable marker of tissue perfusion. Clinical studies have demonstrated that high PslCO2 values and, especially, high gradients between PslCO2 and arterial PCO2 (DPsl-aCO2) are associated with impaired microcirculatory blood flow and a worse prognosis in critically ill patients. Although some questions remain to be answered about sublingual capnometry and its utility, this technique could offer new hope for tissue PCO2 monitoring in clinical practice.