[Venous oximetry: physiology and therapeutic implications]

Abstract

Objectives: The aims of this review are to point out the determinants of oxygen saturation of the haemoglobin of mixed venous blood (SvO(2)), to specify the correlations existing between SvO(2) and central venous saturation in superior vena cava (ScvO(2)), to determine and finally to locate the current place of venous oximetry in clinical practice.

Data sources: A PubMed database research in English and French languages published until December 2006. The keywords were mixed venous blood oxygen saturation; oxygen consumption; oxygen delivery; oxygen extraction; tissue hypoxia; central venous oxygen saturation.

Data extraction: Data in selected articles were reviewed, clinical and basic science research relevant information was extracted.

Data synthesis: The SvO(2) reflects the peripheral extraction of oxygen (O(2)), O(2) delivery and consumption. Its value is related to four determinants: the O(2) consumption (VO(2)), cardiac flow (CF), haemoglobin level (Hb) and O(2) saturation of the haemoglobin of arterial blood (SaO(2)). ScvO(2) is more easily measurable than SvO(2). Under physiological conditions its value is 2 to 3% lower than that of SvO(2). In the critically ill patient, its value is 5% higher than that SvO(2). In most patients, changes in ScvO(2) values parallel those in SvO(2). The clinical interest of the monitoring of venous oximetry was underlined in cases of severe sepsis and septic shock, and during the perioperative period of major surgery.

Conclusion: The management of patients in critical states with therapeutic goals integrating the monitoring of venous oximetry may reduce the morbidity and mortality of patients undergoing major surgery or hospitalised in the intensive care unit.