Near-infrared spectroscopy during stagnant ischemia: a marker of ScvO₂–SvO₂ mismatch in septic patients with low cardiac output

Introduction

Monitoring of oxygen saturation in the superior vena cava (ScvO₂) was suggested as a simpler and cheaper assessment of the global DO₂:VO₂ ratio and was used successfully as a goal in treatment of patients with septic shock and severe sepsis [1]. In patients with low cardiac output (CO) the difference between SvO₂ and ScvO₂ is more expressed and problematically large confidence limits and poor correlation were found between the two values [2]. The thenar muscle oxygen saturation (StO₂) measured with near-infrared spectroscopy (NIRS) during stagnant ischemia (cuff inflation-induced vascular occlusion) decreases slower in septic shock patients [3]. This may be due to slower muscle tissue oxygen consumption in sepsis. This phenomenon possibly contributes to the ScvO₂–SvO₂ mismatch in patients with low CO by adding more oxygenated venous blood to flow through the superior vena cava. The aim of present study was to determine the relationship between the StO₂ deceleration rate and the ScvO₂–SvO₂ difference in septic patients with low CO.

Methods

In septic patients with low CO and no signs of hypovolaemia, catheterization with a pulmonary artery floating catheter was performed. Blood was drawn from the superior vena cava and pulmonary artery at the time of each StO₂ measurement in order to determine ScvO₂ and SvO₂. The thenar muscle StO₂ during stagnant ischemia was measured using NIRS (InSpectra™) and the StO₂ deceleration rate (StO₂%/min) was obtained using the Inspectra Analysis Program V2.0.

Results

Fifty-four patients (47 male, seven female), age 68 ± 13 years, SOFA score 12.2 ± 2.5 points. CI 2.5 ± 0.7 l/min/m², SvO₂ 67 ± 10%, ScvO₂ 77 ± 8%. Lactate 3.5 ± 3.0 mmol/l, CRP 127 ± 78 mg/l. NIRS data: basal StO₂ 89 ± 8%, deceleration rate -12.6 ± 4.9%/min, StO₂ deceleration rate versus ScvO₂–SvO₂ 0.651, P = 0.001(Pearson correlation, P value).

Conclusion

The StO₂ deceleration rate during cuffing is inversely proportional to the difference between ScvO₂ and SvO₂ in septic patients with low CO. When using ScvO₂ as a treatment goal, this simple noninvasive NIRS measurement might be useful to discover those patients with normal ScvO₂ but probably abnormally low SvO₂.