SummaryCentral venous catheterisation is commonly performed during major surgery and intensive care, and it would be useful if central venous oxygen saturation could function as a surrogate for mixed venous oxygen saturation. We studied 50 patients undergoing living related liver transplantation. Blood samples were taken simultaneously from central venous and pulmonary artery catheters at nine time points during the pre-anhepatic, anhepatic, and postanhepatic phases. Four hundred and fifty sets of measurement were obtained. There was a good correlation between central venous oxygen saturation and mixed venous oxygen saturation. The mean (SD) difference (95% limit of agreement) was lowest at the first time point (1.06 (0.65)%, )1.94% to 2.7%) and then increased throughout the study but remained acceptable. The change in mixed venous oxygen and central venous oxygen saturations occurred mostly in parallel and as a result changes in mixed venous oxygen saturation were reflected adequately in the change in central venous oxygen saturation. The correlation between mixed venous oxygen saturation and cardiac output was poor. True mixed venous blood is derived from a pool of venous blood entering the pulmonary artery via the great veins in the chest. It contains blood which has traversed all systemic capillary beds capable of extracting oxygen, and is thoroughly mixed by the right ventricle. It has been suggested that the most suitable sites with respect to complete mixing are the right ventricular outflow tract and pulmonary artery [1,2]. Mixed venous oxygen saturation has been shown to be a surrogate for the balance between systemic oxygen delivery and consumption during treatment of critically ill patients [3]. Maintenance and monitoring of tissue oxygenation is one of the most important goals in the care of critically ill or unstable patients. Measurement of mixed venous oxygen saturation (Svo 2 ) requires placement of a pulmonary artery catheter, which may not be feasible in all patients. However, central venous access can be easily and safely obtained in both ICU and non-ICU settings, which makes central venous oxygen saturation (Scvo 2 ) monitoring a convenient surrogate for Svo 2 . There has been considerable debate regarding whether Scvo 2 is a satisfactory substitute for Svo 2 , particularly above 65% [4][5][6]. Although the absolute values of Scvo 2 and Svo 2 differ, previous studies have shown close tracking of the two measurements across a wide range of haemodynamic conditions [7].Profound haemodynamic and metabolic changes occur during adult orthotropic liver transplantation (OLT) [5,6]. During the dissection phase the disturbance is mainly due to bleeding and hypovolemia [8], while in the anhepatic phase there may be a 50% reduction of venous return with clamping of inferior vena cava [9]. Reperfusion of the graft during the neo-hepatic stage carries the risk of systemic hypotension (postreperfusion syndrome) [10]. The relationship between Svo 2 and Scvo 2 has not assessed in such conditions where haemody...
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