Evaluating microcirculation
Video images of the sublingual microcirculation were obtained using a handheld Cytocam IDF video microscope (Braedius Medical, Huizen, the Netherlands). This tool is developed to register the microcirculation in organ surfaces. The IDF imaging principle is based on the absorbance, by hemoglobin, of the green light (wavelength: 530 nm) emitted by the microscope. Consequently, red blood cells are visualized as black or gray dots.It is impossible to visualize the vessel walls using this device, and the capillaries are only visible when filled with red blood cells [A recently published validation study demonstrated that Cytocam IDF imaging offers better image quality than SDF imaging [After gently removing saliva with isotonic saline-drenched dressing, the microscope was applied to the sublingual mucosa while avoiding pressure artifacts, and image sequences from at least three sections were captured. Trained investigators used validated AVA v.3.2 software (AVA, MicroVision Medical BV, Amsterdam, the Netherlands) in the blinded analysis of video clips. The clips were arranged in a random order to avoid coupling. Expert recommendations [Each image was divided into four equal quadrants, whereby the flow in each was quantified by eye (0, no flow; 1, intermittent flow; 2, sluggish flow; 3, continuous flow) for each vessel diameter cohort (small, 10–20 μm; medium, 21–50 μm; large, 51–100 μm). The microvascular flow index (MFI) was calculated as the sum of each quadrant score divided by the number of quadrants in which the vessel type was visible. The final MFI was an average of at least 12 quadrants (three regions, four quadrants per region) derived from the overall flow impressions for all vessels within a particular range of diameters in a given quadrant [