**4. Assessment of microcirculation**

The assessment of these factors can be analysed in five parameters: (i) total microvascular density (TVD), (ii) perfused microvascular density (PVD), (iii) proportion of perfused microvessels (PPV), (iv) microvascular flow index (MFI) and (v) heterogeneity of microvascular flow index. The first two reflect density, (iii) and (iv) reflect the flow, and (v) represents the heterogeneity of flow. Microcirculatory blood flow can be detected at the bedside by videomicroscopic techniques, and by laser Doppler flowmetry, near-infrared spectroscopy (NIRS), tissue reflectance spectrophotometry, or by tonometry. These techniques provide simple and quantitative data. Biochemical parameters that show microcirculation are reliable and include lactate, tissue CO2 content and venous oxygen saturation.
