Table 2.

Microcirculation variables analyzed after image acquisition.

Variable	Abbreviation	Definition	Description
Proportion of perfused vessels	PPV	Grid-based score (3 horizonal and vertical lines). Percentage of perfused vessel per total number of vessel crossings	Binominal determination of red blood cell velocity: -Flow -No flow
De Backer score	–	Grid-based score (3 horizonal and vertical lines). Vessel crossings per grid length	Proxy of total vessel density, includes different vessel types. Together with PPV proxy of FCD
Microvascular flow index	MFI	Grid-based score per quadrant: 0 = stop flow 1 = intermittent flow 2 = sluggish flow 3 = normal flow	Assesses average red blood cell velocity per quadrant. Good reproducibility.
Total vessel density	TVD	Software supported, Total vessel area per surface area	Presents as an absolute number. Time-consuming analysis requiring manual correction of software supported vessel tracing. Measures vessel diameter.
Perfused vessel density	PVD	Percentage of perfused vessels × TVD	Similar to functional capillary density (FCD). Time consuming analysis
Heterogeneity index	HI	Coefficient of variation. Highest-lowest value/mean	Determines the heterogeneity of blood flow. Provides additional information. Calculation can use MFI or PPV
Functional capillary density (26)	FCD	Sum of the length of all capillaries containing moving RBCs

Adapted from (10).