Impact of oxygenator design on hemolysis, shear stress, and white blood cell and platelet counts

Objective: To determine whether relative pressure drop, shear stress, hemolysis, and white blood cell and platelet counts are influenced by different oxygenator designs. To compare the oxygenator results with the average shear stress over an arterial cannula. Design: Prospective; patients enrolled consecutively. Setting: University hospital. Participants: Three groups of 12 adult patients, scheduled for routine cardiac surgery. Interventions: Each group was submitted to a different oxygenator design: group 1 to a high-pressure hollow-fiber membrane oxygenator (Sarns Turbo); group 2 to a medium-pressure hollow-fiber membrane oxygenator (Cobe Optima); and group 3 to a flat-sheet membrane oxygenator (Cobe Duo). Measurements and Main Results: Although the investigated oxygenators have important differences in pressure drop and shear stress, no statistical differences were found in hemolysis generation or blood handling among the different groups. Actually, the study shows much higher shear stress levels over an average arterial cannula than over any of the evaluated oxygenators. Conclusions: the pressure drop over an oxygenator does not correlate well with shear stress and hemolysis because the dimensions of the system (radius and length) must be included in the calculation of shear stress from pressure drop. Copyright (C) 1996 by W.B. Saunders Company