Oxygen transport rate and erythrocyte deformability.
While commenting on what are seemingly contradictory results, Buchwald and Menchaca1 appropriately recognize important differences between our 2 studies.2,3 In their study, they demonstrated an increased rate of oxygen transport with red blood cells that were stored for longer duration compared with fresh red blood cells.2 These findings are intriguing, but without a demonstrated mechanism, they leave us wondering how red blood cells may be more effective in delivering oxygen after prolonged storage in the blood bank. In our very different study, we measured red blood cell membrane deformability and showed loss of deformability after longer storage intervals >21 days).3 We and others have proposed that loss of membrane deformability impairs red cell ability to traverse capillary beds, because the diameter of the red blood cell is virtually the same dimension as the capillary lumen. In Buchwald's study, it is unlikely that any loss of deformability during storage would have influenced their measured rate of oxygen transport since their model used a simulated capillary bed made of Silastic tubing with a 100 mm internal lumen diameter a diameter roughly 15 times greater than a typical human capillary (approximately 7 mm) Furthermore, neither of our studies measured other important parameters that shift the hemoglobin oxygen dissociation curve, thus altering oxygen transport, such as 2,3 diphosphoglycerate, pH, or Pco2 concentrations, all of which have been shown to be abnormal after longer durations of blood storage.4 Other adverse changes in red blood cells occurring during storage include loss of nitric oxide5 and increased endothelial adherence,6 both of which may impair blood flow and result in decreased oxygen delivery. These parameters also would not have been accounted for in an in vitro study. We conclude by agreeing with Buchwald and Menchaca1 that there are many complex changes that occur during blood storage and that more research is needed to determine which parameters of the "storage lesion" are most clinically relevant and whether fresher red blood cells are more effective in delivering oxygen.
Anesthesia and analgesia