Changes in immune function induced by CPB

· Cardiac surgical patients are more susceptible to infection due to the effects of CPB on the immune system

· Alterations in almost every component of the immune system occurs after CPB

Effects on Humoral Immunity

· Hemodilution —> dilution of immunoglobulins and complement

· Air-fluid interface trauma to Ig (denaturation)

· Exposure to oxygenator —> denaturation of immunoproteins

· Denatured immunoproteins constitute one stimulus to complement activation during CPB

· Complement activation occurs during CPB and is associated with neutrophile activation

· Respiratory complications correlate with the degree of complement activation

· Hypothermia, hemodilution & heparin reduce complement activation and subsequent neutrophile response and may protect the patient from harmful sequelae

· Circulating bradykinin increases during hypothermia and CPB and may contribute to altered vascular permeability and circulatory instability

Effects on Cellular Immunity

· Effect of CPB on cellular immunity is both direct & indirect

· Leukocyte & lymphocyte counts fall with the onset of CPB

· Bubble oxygenators cause a greater drop in white cell count than membrane oxygenators

· Bone marrow is stimulated by CPB

· After CPB, white cell count increases, while immunoglobulin & complement remain decreased

· Preoperative white cell counts are rapidly restored after concluding the bypass and indeed it is usual for a pronounced leukocytosis to persist for several days postoperatively

· Exposure of white cells to circuit —> alteration in cellular function with

i) decreased phagocytic activity

ii) decreased response to chemotactic stimulus

· Cardiotomy suction & bubble oxygenators depress serum opsonisation capacity

· Membrane oxygenators preserve serum opsonisation capacity

· Some lymphocyte changes observed after CPB are similar to those observed after blood transfusions