Regional capnometry to evaluate the adequacy of tissue perfusion
Tissue hypoperfusion is a major cause of morbidity and mortality in critically ill patients but cannot always be detected by measuring standard whole-body hemodynamic and oxygen-related parameters (e.g., blood pressure, cardiac output, and central venous oxygen saturation). Preclinical and clinical studies have demonstrated that low-flow states are consistently associated with large increases in venous and tissue PCO2. Monitoring regional PCO2 with gastric tonometry (PgCO2) is known to have independent prognostic value for predicting postoperative complications and mortality. The PgCO2 gap might also be of value as a treatment target (endpoint) in critically ill patients. However, this tool has several limitations and has not yet been developed commercially, thus restricting its use. Regional capnography with sublingual and transcutaneous sensors might be an alternative noninvasive option for evaluating the adequacy of tissue perfusion in critically ill patients. However, further studies are needed to determine whether or not this monitoring technique is of value—particularly as an endpoint for guiding resuscitation. Bladder PCO2, has only been evaluated in animal studies, and so remains to be validated in patients.