Near-infrared spectroscopy for assessing the tissue oxygen extraction rate during sepsis: relationship with outcome

Introduction

Microcirculatory dysfunction impairs tissue oxygenation during sepsis. We applied near-infrared spectroscopy (NIRS) to evaluate the tissue oxygen extraction rate in sepsis and its relationship with outcome.

Methods

A prospective observational study; 14 septic patients underwent NIRS monitoring (thenar eminence) with a vascular occlusion test (using a 40% StO₂ target) at admission to the ICU. Healthy volunteers (n = 27) were studied as controls. The slope of the desaturation curve was assessed separately for the first (StO₂ down1) and the last part (StO₂ down2) of the curve and the difference between, Down2 - Down1, was calculated.

Results

StO₂ Down1 was lower in healthy volunteers as compared with septic patients (P < 0.05); no difference was seen between ICU survivors (n = 7) and nonsurvivors (n = 7). StO₂ Down2 was similar between healthy volunteers and ICU survivors, while it was higher in nonsurvivors (P < 0.01 vs. healthy). ICU nonsurvivors showed higher Down2 - Down1 as compared with ICU survivors (P < 0.01, Figure 1).

Figure 1

Conclusion

Tissue oxygen extraction was reduced in septic patients. Nonsurvivors showed a flattening in the last part of the desaturation curve during a VOT, while the first part of the StO₂ downslope did not show any difference between survivors and nonsurvivors. This may reflect a tissue hypometabolic status, which may be better elicited in the final part of the ischemic challenge.