Clinical review: use of venous oxygen saturations as a goal - a yet unfinished puzzle

Shock is defined as global tissue hypoxia secondary to an imbalance between systemic oxygen delivery (DO2) and systemic oxygen demand (VO2). Unrecognised and untreated global tissue hypoxia increases morbidity and mortality. Accurate detection of global tissue hypoxia is therefore of vital importance. Physical findings, vital signs, measuring central venous pressure and urinary output are important but insufficient for accurate detection of global tissue hypoxia [1-3]. Measurement of mixed venous oxygen saturation (SvO2) from the pulmonary artery has been advocated as an indirect index of tissue oxygenation [4]. As a result of an extensive debate in the literature [5-7], however, use of the pulmonary artery catheter has become somewhat unpopular. In contrast, insertion of a central venous catheter in the superior vena cava via the jugular of the subclavian vein is considered standard care in critically ill patients. Just like SvO2, the measurement of central venous oxygen saturation (ScvO2) has been advocated in order to detect global tissue hypoxia.Venous oxygen saturations have been the subject of research for over 50 years, but especially over the past decade the amount of literature describing changes in ScvO2 and SvO2 in critically ill patients, including high-risk surgical patients, increased substantially. This led to high expectations with respect to the use of venous oxygen saturation as a therapeutic goal. The aim of the present review is to summarise the evidence and to discuss the clinical utility of both SvO2 and ScvO2 in the treatment of critically ill patients, including high-risk surgical patients.We performed a search of the PUBMED database from 1980 to 2010 using combinations of the following terms: SvO2, ScvO2, venous oxygen saturation, venous saturation, critically ill, shock, septic shock, high risk surgery, surgery, operation. The articles published in English were included when published in a peer-reviewed journal. The clinical investigations