The OxyCam: A novel hand-held vital microscope for quantitative measurement of microcirculatory perfusion and oxygenation

Background Hand-Held Vital Microscopy (HVM) has been utilized in clinical investigations to measure microcirculation, providing valuable insights into the pathophysiology of critical illness and its treatment. However, its clinical implementation has been hampered by several shortcomings. These included the need for automatic analysis software, for instant image stabilization, and for information regarding microcirculatory oxygenation. The aim of this study is to describe an HVM which has realized these research objectives. Methods This preclinical study introduces the OxyCam, a novel HVM device. OxyCam stabilizes images during recording and subsequently provides essential microcirculatory functional parameters through automatic analysis. Green and blue illuminated images, sequentially recorded and ratio imaged, allow calculation of the hemoglobin (Hb) oxygen saturation (µHbO 2 sat) of RBCs and are presented in pseudo color images. We validated the OxyCam on the hindlimb muscle of 9 male Wistar albino rats, mechanically ventilated at different levels of inspired oxygen (FiO 2 ). Comparison was made between OxyCam-green and blue images and to its predecessor the Cytocam. OxCam-generated µHbO 2 sat values were compared to HbO 2 sat fiber spectrophotometry (O2C). Results Green and blue illumination from the OxyCam yielded higher total vessel density (OxyCam green [31.4±4.3] mm/mm 2 ; OxyCam blue [32.5±4.2] mm/mm 2 , Cytocam [28.5±3.6] mm/mm 2 ) and functional capillary density (OxyCam green [25.4±6.4] mm/mm 2 ; OxyCam blue [26.2±7.9] mm/mm 2 ; Cytocam [23.0±4.5] mm/mm 2 ) than the Cytocam images OxyCam-blue gave higher tissue RBC perfusion values (OxyCam green [55.3±18.0] µm/min; OxyCam blue [69.5±25.5] µm/min; Cytocam [58.3±15.3] µm/min) than the OxyCam-green or Cytocam images. OxyCam-blue and green images gave better image quality than the Cytocam images. µHbO 2 sat imaging with the OxyCam was validated by demonstrating expected changes in µHbsat during different FiO 2 levels (100%, 60%, 21%, 0%). Furthermore, a correlation between the mean µHbO 2 sat of images and independently measured µHbsat by tissue spectrophotometry during different levels of FiO 2 was found. Finally, µHbO 2 sat images in pseudo-color (red to blue) are shown for the individual microvessels at different FiO 2 levels. Conclusions The OxyCam has been validated for measuring tissue perfusion and oxygenation and can be considered for point-of-care diagnosis of the microcirculation at the bedside.