Table 2 Microcirculation parameters

Microvascular flow index

Perfusion quality (for small, medium, and large vessels^a)

MFI

Arbitrary

The image is divided into four quadrants; a number is assigned for each quadrant according to the predominant type of flow (0 = no flow; 1 = intermittent; 2 = sluggish; 3 = continuous). The MFI results from the averaged values

[7, 14, 41, 54]

De Backer score

Vessel density

\( \mathrm{V}{{\mathrm{D}}_{De}}_{Bac \ker}\kern0.5em =\kern0.5em Nx/L\mathit{\mathsf{g}} \)

1/mm

The image is divided by three vertical and three horizontal lines; the De Backer score is calculated as the number of vessels crossing the lines divided by the total length of the lines

[7, 14, 41–43]

Total vessel density

Vessel density (for small, medium, and large vessels^a)

TVD = L _v /A _FOV

mm/mm²

Total length of vessels is divided by the total surface of the analyzed area

[14, 41]

Proportion of perfused vessels (by length)

Perfusion quality (for small, medium, and large vessels^a)

PPV₁ = L _p /L _v

Percent

100 × number of perfused vessels is divided by the total number of vessels

[14, 41, 43]

Proportion of perfused vessels

PPV = N _p /N _v

Percent

100 × length of perfused vessels divided by total length of vessels

[7]

Flow heterogeneity index

Perfusion heterogeneity

FHI = (MFI _max  − MFI _min )/MFI _avg

Unitless

The difference between the highest MFI and the lowest MFI is divided by the mean MFI. MFI is intended as the averaged MFI of each site

[14, 41]

Perfused vessel density

PVD = PPV * VD_De Backer

1/mm

Vessel density × proportion of perfused vessels

[41]

Perfused vessel density

Functional vessel density (for small, medium, and large vessels^a)

\( \begin{array}{l}\mathrm{P}\mathrm{V}\mathrm{D}\kern0.5em =\kern0.5em {L}_p/{A}_{FOV}\kern0.5em \mathrm{or}\kern0.5em \\ {}\mathrm{P}\mathrm{V}\mathrm{D}\kern0.5em =\kern0.5em \mathrm{P}\mathrm{P}{\mathrm{V}}_1\kern0.5em *\kern0.5em \mathrm{T}\mathrm{V}\mathrm{D}\end{array} \)

mm/mm²

Total length of perfused vessels (sluggish or continuous) is divided by the total surface of the analyzed area (%)

[14, 36]