Assessment of the microcirculatory flow in patients in the intensive care unit.

Various techniques have been used at bedside to assess the microcirculation of critically ill patients, including nailfold videomicroscopy, laser doppler techniques, and orthogonal polarization spectral imaging. Nailfold videomicroscopy was introduced first, but its value may be limited by the extreme sensitivity of nailfold microcirculation to external temperature or vasoconstrictive agents. Laser Doppler techniques can measure gastric or jejunal mucosal blood flow as well as skin and muscle blood flow, but do not take into account blood flow heterogeneity, a major parameter of microcirculation. The recent introduction of orthogonal polarization spectral imaging techniques allows direct visualization of microcirculation in critically ill patients, opening a new area for the investigation of the pathophysiologic processes involved in the hemodynamic alterations of shock states.