Microcirculatory oxygenation and shunting in sepsis and shock

Objective: To review optical spectroscopic techniques for assessment of the determinants of tissue oxygenation and to evaluate the notion that the dis turbances in oxygen pathways in sepsis can be accounted for by enhanced fun ctional shunting of parts of the microcirculation. Data Resources: Experimental data from previous research and the literature were analyzed. Study Selection:The data selected pertained to a) whether cellular distress in sepsis is caused by tissue hypoxia or disturbed metabolic pathways, b) optical spectroscopic techniques used to study microcirculatory oxygenation , and c) possible mechanisms underlying shunting of the microcirculation in hypoxemia and sepsis. Study Synthesis: Despite resuscitation of oxygen-derived variables, signs o f regional tissue hypoxia persist in sepsis. The mechanisms underlying this condition are expected to be associated with oxygen pathways in the microc irculation. Optical spectroscopic techniques are providing new insights int o these mechanisms. These include absorption spectroscopy for hemoglobin sa turation of erythrocytes, reduced nicotinamide adenine dinucleotide fluores cence for tissue mitochondrial bioenergetics, and palladium-porphyrin phosp horescence for microvascular Po-2. Reduced nicotinamide adenine dinucleotid e videofluorescence studies have shown the heterogeneous nature of hypoxia. Measurement of gut microvascular Po-2 in pigs has shown the development of a Po-2 gap between microvascular Po-2 and venous Po-2 during hemorrhage an d endotoxemia, with a larger gap occurring in sepsis than in hemorrhage. It is hypothesized that this difference is caused by the enhanced shunting of the microcirculation present in sepsis. Conclusions: Microcirculatory distress may form one of the earliest stages in the progress of sepsis to multiple organ failure, and shunting of the mi crocirculation may be an important contributing factor to this development. To evaluate the severity of microcirculatory distress and the effectivenes s of resuscitation strategies, new clinical technologies aimed at the micro circulation will need to be developed. It is anticipated that optical spect roscopy will play a major role in the development of such tools.