The Correlation of Near-Infrared Spectroscopy with Changes in Oxygen Delivery in a Controlled Model of Altered Perfusion

Abstract

Alterations in regional tissue perfusion may precede global indications of shock. This study compared regional tissue oxygenation saturation (StO2) using near-infrared spectroscopy with standard hemodynamic and biochemical variables in 40 patients undergoing cardiopulmonary bypass (CPB). Mean arterial pressure, cardiac output, oxygen delivery, arterial blood gases, and lactate were recorded at specific intervals during surgery. Data were organized by stage of procedure, and the relationship of StO2 to established parameters was investigated. With initiation of CPB, StO2 declined by 12.9 per cent (standard deviation +/- 14.75%) with a delayed increase in lactate from 0.9 (interquartile range [IQR], 0.6-1.5) mmol/L to 2.3 (IQR, 1.8-2.5) mmol/L. The minimum StO2 value preceded the maximum lactate level by an average time of 93.9 (standard deviation +/- 86.3) minutes. Additionally, a decrease in StO2 corresponded with an increase in base deficit of 4.84 (standard deviation +/- 2.37) mEq/L over the same period. Calculated oxygen delivery decreased from a baseline value of 754 (IQR, 560-950) mL/min to 472 (IQR, 396-600) mL/min with initiation and maintenance of CPB. For patients undergoing CPB, StO2 is a reliable, noninvasive monitor of perfusion, which correlates well with oxygen delivery and identifies perfusion deficits earlier than lactate or base deficit.