Tissue partial pressure of carbon dioxide tension measurements and microcirculation visualization : New techniques for study low flow states

Microcirculation is the ultimate determinant of the outcomes of circulatory shock states. Microcirculatory function is the prerequisite for adequate tissue oxygenation and therefore organ function. It transports oxygen and nutrients to tissue cells, ensures adequate immunological function and, during disease, delivers therapeutic drugs to target cells. It ismadeup of the smallest blood vessels: arterioles, capillaries and venules [1] (Fig. 1). The previous techniques used for studying microcirculation (microscopes, laser Doppler or plethysmography) were able to provide only a global measurement of microvascular blood flow; a measurement expressed as an average value of whatever was the diameter or direction of single vessels. Recent technological developments allow more precise and direct investigation of the tissue perfusion, and especially of the microcirculatory blood flow. The new techniques are basically noninvasive measurements of tissue carbon dioxide tension (PCO2), for example at the oral cavity mucosa, and the orthogonal polarisation spectral (OPS) imaging techniques, which have allowed direct visualisation and monitoring of microcirculation at the bedside .