Near-infrared spectroscopy technique to evaluate the effects of red blood cell transfusion on tissue oxygenation

Abstract

Introduction: The aim of this study was to evaluate the effects of red blood cell (RBC) transfusions on muscle tissue oxygenation, oxygen metabolism and microvascular reactivity in critically ill patients using near-infrared spectroscopy (NIRS) technology.

Methods: This prospective, observational study included 44 consecutive patients hospitalized in the 31-bed, medical-surgical intensive care unit of a university hospital with anemia requiring red blood cell transfusion. Thenar tissue oxygen saturation (StO2) and muscle tissue hemoglobin index (THI) were measured using a tissue spectrometer (InSpectra Model 325; Hutchinson Technology Inc., Hutchinson, MN, USA). A vaso-occlusive test was performed before and 1 hour after RBC transfusion by rapid inflation of a pneumatic cuff around the upper arm. The following variables were recorded: THI, the StO2 desaturation slope during the occlusion (%/minute) and the StO2 upslope of the reperfusion phase following the ischemic period (%/second). Muscle oxygen consumption (NIR VO2; arbitrary units) was calculated as the product of the inverse StO2 desaturation slope and the mean THI over the first minute of arterial occlusion.

Results: Blood transfusion resulted in increases in hemoglobin (from 7.1 (6.7 to 7.7) to 8.4 (7.1 to 9) g/dl; P < 0.01) and in oxygen delivery (from 306 (259 to 337) to 356 (332 to 422) ml/minute/m2; P < 0.001). However, systemic VO2 was unchanged. RBC transfusion did not globally affect NIRS-derived variables, but there was considerable interindividual variation. Changes in the StO2 upslope of the reperfusion phase after transfusion were negatively correlated with baseline StO2 upslope of the reperfusion phase (r2 = 0.42; P < 0.0001). Changes in NIR VO2 after transfusion were also negatively correlated with baseline NIR VO2 (r2 = 0.48; P = 0.0015). There were no correlations between RBC storage time and changes in StO2 slope or NIR VO2.

Conclusions: Muscle tissue oxygenation, oxygen consumption and microvascular reactivity are globally unaltered by RBC transfusion in critically ill patients. However, muscle oxygen consumption and microvascular reactivity can improve following transfusion in patients with alterations of these variables at baseline.

Figure 1

Relationship between baseline and change in thenar tissue oxygen saturation reperfusion phase upslopes. x axis: Baseline thenar tissue oxygen saturation (StO₂) upslope of the reperfusion phase (%/second); y axis: the difference between the StO₂ upslopes of the reperfusion phase after and before transfusion (%/second). r² = 0.42; P < 0.0001.

Figure 2

Relationship between baseline muscle oxygen consumption and change in muscle oxygen consumption. x axis: baseline muscle oxygen consumption (NIR VO₂; arbitrary units); y axis: difference in NIR VO₂ after and before transfusion (ΔNIR VO₂; arbitrary units). NIR VO₂ was calculated as the product of the inverse value of the thenar tissue oxygen saturation (StO₂) desaturation slope and the mean tissue hemoglobin index over the first minute of arterial occlusion. r² = 0.48; P = 0.0015.