This thesis contributes to the quest to better understand, monitor and predict outcomes of critically ill patients in circulatory shock who are at risk of oxygen deficits in tissues and cells. In... Show moreThis thesis contributes to the quest to better understand, monitor and predict outcomes of critically ill patients in circulatory shock who are at risk of oxygen deficits in tissues and cells. In the studies performed, we explored hypoxia severity in tissue and cells in addition to the commonly used parameters for perfusion and oxygenation in critically ill patients. We investigated the added predictive value of lactate and lactate clearance to the Acute Physiology and Chronic Health Evaluation IV model for predicting in-hospital mortality in critically ill patients with sepsis. We subsequently validated the findings in the Medical Information Mart for Intensive Care cohort. We also studied characteristics of the recently developed protoporphyrin IX-triple state lifetime technique. This measures mitochondrial oxygenation tension (mitoPO2) in vivo at the bedside. We examined the variability of the mitoPO2 measurements between and within healthy subjects. Next, we similarly assessed mitoPO2 values at various timepoints in critically ill patients with anemia before and after red blood cell transfusions and examined the associations between mitoPO2 and other parameters of critical illness and of tissue oxygenation and perfusion in critically ill patients. Show less