Background: Restoration of adequate tissue oxygenation is the goal of shock resuscitation. Commonly, central venous oxygen saturation and lactate clearance are used to monitor this therapeutic endpoint in sepsis. Tissue oxygen saturation (StO2) obtained by near-infrared spectroscopy (NIRS) has been introduced as an alternative.
Objective: To determine the temporal changes of tissue oxygen saturationand central venous oxygen saturation (ScvO2) in severe sepsis/septic shock patients from initial resuscitation to 72 hours after treatment, and to explore the relationship between both parameters including the association with outcomes.
Material and Method: A prospective, observational study was performed in a single center 14-bed university hospital, Medical Intensive Care Unit. The present study enrolled severe sepsis/septic shock patients aged >18 years. Central venous oxygen saturation and tissue oxygen saturation were measured at 0-1st hour (right after central venous catheter was placed), 1st-6th hour (the point when hemodynamic goal was achieved), 6th-9th hour, 9th-12th hour, 24th hour, 48th hour, and 72th hour in simultaneous fashion.
Results: Thirty-five patients were enrolled and 170 paired-measurements were made. During the first 24 hours, both tissue and central venous oxygen saturation gradually increased in the same direction. However, only fair correlation was observed (r = 0.253, p = 0.01) and the agreement was not satisfactory. Mean StO2 during the first 24 hours was higher in survived patients ((82.6+9.3 vs. 74.3+16.0, p = 0.016). When partitioned ScvO2 into ranges, namely ScvO2 <60%, 60-64%, 65 69%, 70-74%, 75-79%, 80-84% and >85%, the corresponding StO2 values were found randomly throughout the ScvO2 ranges, without specific predilection.
Conclusion: The temporal changes of StO2 and ScvO2 during sepsis/septic shock resuscitation were demonstrated. Their correlation and agreement were not satisfactory. No specific StO2 value for the reversal of tissue hypoxia was observed. More studies are needed to explore the benefit of StO2 as a bedside tool for tissue perfusion monitoring.

Keywords: Tissue oxygen saturation, StO2, Central venous oxygen saturation, Near-infrared spectroscopy, NIRS, Severe
sepsis, Septic shock