Mark Wefers Bettink

Chapter 3 52 (VO 2 (t)) and Diffusive Oxygen Influx into the measurement volume (DOI(t)). The method to calculate ODR from the mitoPO 2 kinetics is: The VO 2 (t) is oxygen-dependent and, according to Michaelis-Menten kinetics, can be described as: Where V max is the not supply-dependent maximal tissue oxygen consumption and P 50 is the PO 2 at which cellular oxygen consumption is reduced to ½ V max . PO 2 (t) denotes the PO 2 in the measurement volume at time point t. 2.8 In human measurements Using COMET a dynamic measurement was performed on a healthy volunteer. Preceding the measurements an ALA plaster 4 cm 2 (2mg 5-amino-4oxopentacid / cm 2 ) was applied for approximately 10 hours (overnight) onto the skin of the sternum. A baseline of 20 seconds was measured before the microcirculation was occluded. The microcirculation occlusion was accomplished by application of external pressure by hand on the Skin Sensor. Secondly, we report an incidental finding we made during an ongoing feasibility study of the COMET. The study is performed in accordance with the declaration of Helsinki and patients are consented with a protocol approved by local ethics committee METC (CCMO number NL51937.078.15). This study is set up to determine the applicability, stability, and reproducibility of the COMET measurement over a longer period of time during neurosurgery. The shown incidental finding is an observation that occurred during non- protocolled administration of the central alpha-receptor agonist clonidine. MitoPO 2 was measured intraoperatively, simultaneously to tissue oxygenation saturation and perfusion parameters (O2C, oxygen to see version 2424, Lea Medizintechnik GmbH, Germany). The O2C measures three parameters: The local capillary venous saturation (SO 2 ), the local velocity of blood given in velocity units (VU) and the local micro vascular blood flow given in flow units (FU). Both the COMET Skin Sensor and the O2C probe (LFX- 43) were positioned on the sternum next to each other.