Mark Wefers Bettink

Preface and outline 11 1 The complex pathophysiology of a critically ill patient, especially in severe sepsis and septic shock, requires a multilevel approach. In attempting to understand the interplay between macrocirculation, microcirculation and parenchymal cells, the mitochondria are key players that shouldnot beoverlooked.We see substantial progress in thedevelopment of technologies to assess aspects of mitochondrial function at the bedside, for example direct measurement of mitochondrial oxygen tension and oxygen consumption. 11,12 Measurement of mitoPO 2 and mitoVO 2 The method used to measure mitoPO 2 and mitoVO 2 is described in detail by Mik et al. 11,13 In short, protoporhyrin IX (PpIX) is the final precursor of heme in the heme synthetic pathway. PpIX synthesis takes place in the mitochondria and aminolaevulinic acid (ALA) is the rate limiting product in this process. ALA administration leads to a substantial enhancement of PpIX concentration in the mitochondria. PpIX possesses a triplet state that reacts strongly with oxygen, making its delayed fluorescence lifetime oxygen- dependent according to the Stern-Volmer equation. 14 MitoVO 2 is measured directly after local occlusion of the microcirculation and thus stopping oxygen supply, this is obtainedby local pressure on themeasurement probe. This simple procedure of stopping oxygen supply creates reproducible stop flow conditions and therefore reproduceable mitoVO 2 measurements. The first implementation of this technique was described by Harms et al. 15 Whilst it might be relevant to measure mitochondrial oxygenation and oxygen consumption in sepsis, no golden standard for these measurements exists. In fact, most mitochondrial function tests are invasive or can only be performed in a research setting (NMR and NADH fluorometry). In this thesis, we present the translational journey of a Cellular Oxygen METabolism monitor (COMET) from an animal model to the patient with sepsis. We show the possibility of bedside monitoring of mitochondrial oxygenation (mitoPO 2 ) and mitochondrial oxygen consumption (mitoVO 2 ) for a patient with sepsis. Outline This thesis is divided in 3 parts. Part one focusses on the development of the COMET monitor and its calibration in humans. Part two focusses on the changes in mitochondrial function in a sepsis like experimental model (rat or human volunteers) or during sepsis (patients). Part three focusses on perioperative use of the COMET monitor as a parameter of cellular oxygenation.