From Macrohemodynamic to the Microcirculation

ICU patients need a prompt normalization of macrohemodynamic parameters.
Unfortunately, this optimization sometimes does not protect patients
from organ failure development. Prevention or treatment of organ failure
needs another target to be pursued: the microcirculatory restoration.
Microcirculation is the ensemble of vessels of maximum 100 μm in
diameter. Nowadays the Sidestream Dark Field (SDF) imaging technique
allows its bedside investigation and a recent round-table conference
established the criteria for its evaluation. First, microcirculatory
derangements have been studied in sepsis: they are mainly characterized
by a reduction of vessel density, an alteration of flow, and a
heterogeneous distribution of perfusion. Endothelial malfunction and
glycocalyx rupture were proved to be the main reasons for the observed
microthrombi, capillary leakage, leukocyte rolling, and rouleaux
phenomenon, even if further studies are necessary for a better
explanation. Therapeutic approaches targeting microcirculation are under
investigation. Microcirculatory alterations have been recently
demonstrated in other diseases such as hypovolemia and cardiac failure
but this issue still needs to be explored. The aim of this paper is to
gather the already known information, focus the reader’s attention on
the importance of microvascular physiopathology in critical illness, and
prompt him to actively participate to achieve a more comprehensive
understanding of the issue.