The impact of induction of general anesthesia and a vascular occlusion test on tissue oxygen saturation derived parameters in high-risk surgical patients.

OBJECTIVES: Tissue oxygen saturation (StO(2)) assessed using Near Infrared Spectroscopy and its derived parameters during a vascular occlusion test (VOT) can detect microvascular changes in septic shock patients. General anesthesia (GA) impacts microcirculation. Our aim was to study the effects of general anesthesia on StO(2) and StO(2) derived parameters obtained during VOT in patients referred for cardiac surgery. METHODS: We studied 15 patients referred for cardiac surgery before and after induction of GA. Before GA induction, we also studied 15 healthy volunteers (non patients) in order to compare baseline physiological data between patients and healthy subjects. Hemodynamic and microcirculatory (StO(2), ischemic slope, reperfusion slope, and hyperemic response) data were recorded at each step. We used the Inspectra StO(2) system (Hutchinson Inc, MN, USA) with a sensor placed on the thenar eminence. StO(2) values were obtained at baseline and during a VOT. A sphyngomanometer was placed on the forearm above the StO(2) probe and the cuff was then rapidly inflated 30 mmHg above systolic pressure and was maintained inflated until the StO(2) value reached 40%. It was then rapidly deflated. RESULTS: Healthy volunteers had significantly higher reperfusion slope than patients (348 [251-393] vs. 261 [185-279] %/min; P < 0.05). GA induction induced no significant change in StO(2) value compared to baseline (79 [75-85] vs. 80 [76-86]%; P = 0.57). We observed a significant decrease in ischemic slope (from -12 [-16--8] to -8 [-10--6] %/min; P = 0.004) and in reperfusion slope (from 261 [185-279] %/min to 164 [151-222] %/min; P = 0.008) suggesting a decrease in local metabolic rate and a negative impact on reperfusion reserve induced by anesthesia. CONCLUSION: StO(2) derived parameters during a VOT are impacted by GA induction. These parameters may have potential for microcirculation assessment in patients undergoing surgery.

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