Mark Wefers Bettink

Chapter 11 190 General discussion In the work we presented in this thesis we have shown robustness and sensitivity of the COMET monitoring technique in our pre-clinical work. The main goal, measuring mitochondrial dysfunction in sepsis, was partly achieved in our ICU study, we failed to reach sufficient participants to analyze the data. We were able to measure cellular oxygenation in patients under anesthesia and started to show the additional value of the COMET monitor as a monitor of cellular oxygenation during anesthesia. The electron transport chain and its production of adenosine triphosphate (ATP) is the best-known function of mitochondria. However, the role of mitochondria in homeostasis of the cell is not limited to the production of ATP. Mitochondria play a key-role in calcium metabolism and cell death mechanisms ( Chapter 2 ). Measuring mitochondrial oxygenation in vivo at the bedside may help in determining the role of mitochondrial dysfunction in acute changes during severe illness [1]. We described the journey of the protoporphyrin IX triplet state life technique (PpIX-TSLT) from a laboratory setup to a CE- marked device for use at the bedside. We described the function of COMET monitor and its first use on a patient during neurosurgery in chapter 3. The technique of the COMET monitor has extensively been calibrated in cells, organs and rats [2,3]. The calibration of the monitor in human skin could not be performed in the same way as in the preclinical work, given that complete deoxygenation of the site of measurement by nitrogen admission to healthy volunteers is not considered safe. Using direct pressure on the probe in combination with arterial occlusion of the arm provided the lowest measurable concentration of oxygen in the mitochondria. This approximation of the zero oxygen condition together with the combination of arterial puncture and blockage of mitochondrial respiration allowed for a two-point verification of the calibration constants in man. Measuring cellular oxygen consumption with the COMET monitor by the method of only arterial occlusion showed similar dynamics as the O2C, OxiVenT and INVOS parameters. The dynamic measurement of mitoVO 2 with direct pressure on the probe gave a faster and more pronounced reduction of mitoPO 2 . We showed that earlier calibration in the lab was successfully translated to the COMET monitor (chapter 4). In part two of this thesis we described the changes of mitochondrial oxygen consumption in a lipopolysaccharide(LPS)-induced endotoxemia rat model. Although we measured a decline of mitochondrial respiration in vivo, these changes were not matched by our ex vivo measurements of mitochondrial oxygen consumption ( chapter 5 ). Measurement