Decrease in red blood cell deformability caused by hypothermia, hemodilution, and mechanical stress: Factors related to cardiopulmonary bypass

During extracorporeal circulation in cardiopulmonary bypass (CPB) surgery, blood is exposed to anomalous mechanical and environmental factors, such as high shear stress, turbulence, decreased oncotic pressure caused by diluti on of plasma, and moderate and especially deep hypothermia widely applied d uring CPB in infants. These factors cause damage to the red blood cells (RB Cs), which is manifest by immediate and delayed hemolysis and by changes in the mechanical properties of RBCs. These changes include, in particular, d ecrease in RBC deformability impeding the passage of RBCs through the micro vessels and may contribute to the complications associated with CPB surgery . We investigated in vitro the independent and combined effects of hypother mia, plasma dilution, and mechanical stress on deformability of bovine RBCs . Our studies showed each of these factors to cause a significant decrease in the deformability of RBCs, especially acting synergistically. The impair ment of RBC deformability caused by hypothermia was found to be more pronou nced for RBCs suspended in phosphate buffered saline (PBS) than for RBCs su spended in plasma. The decrease in RBC deformability caused by mechanical s tress was significantly exacerbated by dilution of plasma with PBS. In summ ary, results of our in vitro study strongly point to a possible detrimental consequence of conventional CPB arising from increased RBC rigidity, which may lead to impaired microcirculation and tissue oxygen supply.