Monitoring the microcirculation in the critically ill patient: current methods and future approaches.
OBJECTIVE
To discuss the techniques currently available to evaluate the microcirculation in critically ill patients. In addition, the most clinically relevant microcirculatory alterations will be discussed.


METHODS
Review of the literature on methods used to evaluate the microcirculation in humans and on microcirculatory alterations in critically ill patients.


RESULTS
In experimental conditions, shock states have been shown to be associated with a decrease in perfused capillary density and an increase in the heterogeneity of microcirculatory perfusion, with non-perfused capillaries in close vicinity to perfused capillaries. Techniques used to evaluate the microcirculation in humans should take into account the heterogeneity of microvascular perfusion. Microvideoscopic techniques, such as orthogonal polarization spectral (OPS) and sidestream dark field (SDF) imaging, directly evaluate microvascular networks covered by a thin epithelium, such as the sublingual microcirculation. Laser Doppler and tissue O(2) measurements satisfactorily detect global decreases in tissue perfusion but not heterogeneity of microvascular perfusion. These techniques, and in particular laser Doppler and near-infrared spectroscopy, may help to evaluate the dynamic response of the microcirculation to a stress test. In patients with severe sepsis and septic shock, the microcirculation is characterized by a decrease in capillary density and in the proportion of perfused capillaries, together with a blunted response to a vascular occlusion test.


CONCLUSIONS
The microcirculation in humans can be evaluated directly by videomicroscopy (OPS/SDF) or indirectly by vascular occlusion tests. Of note, direct videomicroscopic visualization evaluates the actual state of the microcirculation, whereas the vascular occlusion test evaluates microvascular reserve.
De Backer
Daniel
D
Department of Intensive Care, Erasme University Hospital, Université Libre de Bruxelles, Route de Lennik 808, 1070, Brussels, Belgium. ddebacke@ulb.ac.be
Ospina-Tascon
Gustavo
G
Salgado
Diamantino
D
Favory
Raphaël
R
Creteur
Jacques
J
Vincent
Jean-Louis
JL
D016638:Critical Illness / Q000401:mortality; D006684:HLA-DR Antigens / Q000097:blood; D006801:Humans; D008833:Microcirculation / Q000502:physiology*; D008991:Monitoring, Physiologic / Q000379:methods*; D018805:Sepsis / Q000276:immunology / Q000401:mortality
D006684:HLA-DR Antigens