Myths and Facts Regarding Lactate in Sepsis M. Nalos, A. S. McLean, and B. Tang Introduction Lactate has a questionable reputation amongst professionals caring for patients with sepsis. The concern is partly justified, as lactate is indeed a sentinel marker of shock and poor prognosis in sepsis [1]. Traditionally, elevated serum lactate is synony- mous of tissue hypoxia, in particular when associated with metabolic acidosis and frequently clinicians guide fluid resuscitation or inotrope/vasopressor use based on that premise [2]. The concept is based on the distinction between two types of gly- colysis: aerobic and anaerobic (insufficient oxygen availability for mitochondrial ATP production), the latter being regarded as the main source of increased lactate [2, 3]. In this chapter, we argue that such a view of pathophysiology in sepsis is more a “habit of mind” then a real phenomenon and has limited clinical relevance [4]. We will argue that lactate is a crucial molecule in energy metabolism, acid base homeostasis and cellular signaling in sepsis largely independent of tissue oxygena- tion. M. Nalos ()  A. S. McLean Department of Intensive Care Medicine, Nepean Hospital Penrith, Australia Department of Intensive Care Medicine, University of Sydney, Nepean Clinical School Penrith, Australia email: mareknalos@gmail.com B. Tang Department of Intensive Care Medicine, University of Sydney, Nepean Clinical School Penrith, Australia Centre for Immunology and Allergy Research, Westmead Millennium Institute Sydney, Australia 69 © Springer International Publishing Switzerland 2016 J.-L. Vincent (ed.), Annual Update in Intensive Care and Emergency Medicine 2016, DOI 10.1007/978-3-319-27349-5_7