Correlation between Tissue Oxygen Saturation and Global Oxygenation Parameters in Emergency Patients: A Pilot Clinical Study

ABSTRACT

PURPOSE: Near-infrared spectroscopy (NIRS) can noninvasively assess changes in tissue oxygen saturation (StO₂). The primary concern of the current study is to determine whether StO₂ can be used as a surrogate for global oxygenation parameters such as central venous oxygen saturation (ScvO₂), lactic acid, and base deficit (BD) in patients presenting to the emergency department (ED). METHODS: This was a prospective, observational study in patients requiring central venous catheter placement, admitted to the ED with complaints classified as infectious and non-infectious etiology. The NIRS sensor (15 mm probe) was applied on the thenar eminence for at least 3 minutes and ScvO₂, arterial lactic acid, and BD were measured during insertion of a central venous catheter. Data were analyzed using a simple correlation and Bland-Altman plot. RESULTS: A total of 120 patients were enrolled in the study and further classified as an infection (n=39) and a noninfection (n=81) group. Lactic acid BD showed significant correlation with StO₂ in total and in non-infection patients but the degree of correlation was weak and these correlations were not observed in infection patients. Approximately 94% of the difference between StO₂ and ScvO₂ was placed within limit of agreement but there was a risk that StO₂ may overestimate ScvO₂ when ScvO₂ becomes lower. When patients were assigned to two groups according to laboratory results (lactic acid 4.0 mmol/L; BD > 3.0 mmol/L; ScvO₂> 65% or 75%), no significant difference in StO₂ was observed between the two groups. CONCLUSION: In ED patients suspected of having systemic hypoperfusion, StO₂ showed a weak correlation with lactic acid and BD in non-infection patients and no correlation in infection patients. In addition, as ScvO₂ decreased, the difference between StO₂ and ScvO₂ showed a tendency to increase, and StO₂ was much higher than ScvO₂ at low ScvO₂ level. Therefore, before using StO₂ as surrogate for ScvO₂, lactic acid and BD in critically ill patients presenting to the ED, further investigation should be conducted to overcome the limitations of NIRS addressed in this study.