The present invention relates to a method of identifying or monitoring circulatory failure in a subject, which method comprises assessing the subject's microcirculation in respect of the following parameters: (a) functional capillary density (FCD)； (b) heterogeneity of the FCD； (c) capillary flow velocity； (d) heterogeneity of capillary flow velocity； (e) oxygen saturation of microvascular erythrocytes (SmvO2)； and (f) heterogeneity of SmvO2； wherein parameters (a) to (d) are assessed visually by microscopy and parameters (e) and (f) are assessed by diffuse reflectance spectroscopy (DRS)； well as apparatus and software designed for performance of such a method.
