This nonrandomized, prospective observational study evaluated oxygen transport and utilization following red blood cell (RBC) or gelatin transfusion for the correction of hypovolemia in 39 post-cardiac surgery patients, and compared outcome to no treatment.

Results show no significant difference in systemic oxygen parameters between the three study groups. The authors’ approach is unique because they concomitantly monitored the sublingual mucosal microcirculatory oxygenation indices (blood flow index, hemoglobin content and saturation). As expected, RBC transfusion increased blood hemoglobin content systemically and at the microvascular level. Microvascular perfusion was unchanged for the different treatments and no treatment. Sidestream dark-field imaging used to evaluate functional microvascular density classifies flow according to four categories in two ranges of vessel sizes. It was shown that RBC transfusion increased “medium vascular (venular) density” but not smaller sized vessels density.

It is unclear how this phenomenon supports the efficacy of RBC transfusion in this patient group since it is interpreted as RBCs pooling in the compliant vessels. The study design limits the interpretation of the efficacy of treatment with RBCs or gelatin, or no treatment because even though patients underwent the same procedure they had significantly different etiological conditions. Nonetheless, studies which monitor both systemic and microvascular effects of transfusion are important since systemic conditions do not always reflect the state of microcirculatory function.

– Amy G. Tsai