Near-infrared spectroscopy monitoring tissue oxygen saturation after cardiac surgery

Introduction

The aim of this study was to compare near-infrared spectroscopy with global parameters of tissue oxygenation after cardiac surgery, such as cardiac output (CI), mixed venous oxygen saturation (SvO₂) or lactate concentration. After cardiac surgery, the circulating blood volume and cardiac function is regularly reduced on the ICU [1]. This results in reduced microperfusion and peripheral vasoconstriction. The noninvasive InSpectra StO₂ monitor (Hutchinson Technology Inc., Hutchinson, MN, USA) measures the oxygen saturation in the microcirculation of the thenar muscle [2].

Methods

Forty patients after cardiac surgery were monitored with a StO₂ monitor and a Swan–Ganz catheter measuring CI and SvO₂ on the ICU. Additionally intermittent lactate and blood gas analysis was performed. ANOVA was used for statistics of results.

Results

The mean Euro-Score of the patients was 6.5 ± 3.7 including 24 aortocoronary bypass, five heart valve, three ascending aorta and eight combined cardiac operations. After admission were significantly reduced (Figure 1). The StO₂, CI and SvO₂ lactate concentration and noradrenaline dose were increased (P < 0.05). On day 1 the noradrenaline dose dropped after fluid substitution, but only the StO₂ value recovered.

Figure 1

Course of StO ₂ , cardiac output, SvO ₂ and lactate concentration.

Conclusion

After heart surgery StO₂ indicated the reduction as well as the recovery of microcirculation early, whereas the lactate concentration and SvO₂ seemed to demonstrate a delayed response especially of recovery. Management of postoperative fluid and catecholamine therapy by StO₂ to optimize microcirculation should be the subject of further studies.