Near-infrared spectroscopy as a potential surrogate for mixed venous oxygen saturation for evaluation of patients with hemodynamic derangements

Introduction

Crookes and colleagues demonstrated that a decreased thenar muscle tissue oxygen saturation may reflect the presence of severe hypoperfusion (shock) in trauma patients better than traditional hemodynamic parameters [1]. Near-infrared spectroscopy (NIRS) may be a novel method for rapidly and noninvasively assessing changes in tissue level oxygenation. The purpose of this study was to compare and correlate NIRS measurements (StO₂) ith central venous blood saturation measurement (ScvO₂) in the setting of compromised systemic perfusion in critical patients in the emergency department (ED).

Methods

A prospective, nonrandomized, observational, study in patients >18 years, admitted to the critical care area (CAT 1) of the ED with various complaints classified as cardiovascular, pulmonary, neurological, trauma or gastrointestinal etiology (n = 500). The NIRS probe was applied to the right thenar eminence and data were collected and stored for analysis. StO₂ and ScvO₂ monitoring was performed within 15 minutes of admission to CAT 1, and values were recorded at a single point in time. The ED physicians were blinded to StO₂ values. Exclusion criteria included the Do Not Resuscitate status, peripheral vascular disease, cardiac arrest, amputated upper extremities or skin abnormalities in the monitoring site as well as refusal to participate.

Results

StO₂ correlation analysis was performed against all continuous variables. Subsequently, ANOVA was run for all of the continuous variables allowing pairwise comparisons. For this cohort of 500 patients, 305 paired data points of StO₂ and ScvO₂ were compared. StO₂ and ScvO₂ had a strong linear correlation that was statistically significant (r = 0.76, P < 0.001). We also observed that the time spent below an StO₂ <75% was associated with an APACHE score greater than 15 and also was associated with a higher admission rate to the ICU (P = 0.05).

Conclusion

NIRS has demonstrated with significance that there is a strong correlation with StO₂ and ScvO₂ in critically ill patients presenting to the ED. There also appears to be an association between the time a patient spends below an StO₂ <75% with an increased APACHE score and ICU admission.