DIASPIRIN CROSS-LINKED HEMOGLOBIN DOES NOT INCREASE BRAIN OXYGEN-CONSUMPTION DURING HYPOTHERMIC CARDIOPULMONARY BYPASS IN RABBITS

Background: Decreased erythrocyte deformability due to cardiopulmonary bypass (CPB) and/or hypothermia, may result in brain capillary beds t hat have decreased erythrocyte transit, resulting in a generalized imp airment of brain oxygenation during CPB. Because brain capillary plasm a now continues even when erythrocyte now is absent, the authors' hypo thesized augmentation of plasma oxygen content with a non-erythrocyte- associated oxygen transport molecule would increase brain oxygen uptak e during hypothermic CPB. Methods: Anesthetized New Zealand white rabb its, maintained on CPB at 27 degrees C, were randomized to one of thre e groups. In group 1 (n = 13), plasma oxygen content was increased by administration of alpha-alpha diaspirin cross-linked hemoglobin. In th is group, pretreatment with 0.5 mg/kg verapamil was necessary to preve nt hypertension. In group 2 (n = 13), alpha-alpha diaspirin cross-link ed hemoglobin was not administered, but verapamil was given as before (control). In group 3 (n = 13), neither alpha-alpha diaspirin cross-li nked hemoglobin nor verapamil was administered (control). At 60 min of CPB, cerebral blood flow (microspheres) and cerebral metabolic rate f or oxygen (Fick) were determined. Results: Systemic physiologic variab les did not differ among groups. Although total arterial oxygen conten t was equivalent in all groups (similar to 12.1 ml O-2/dl), the alpha- alpha diaspirin cross-linked hemoglobin group had a much greater propo rtion of the total arterial oxygen content present in a non-erythrocyt e-associated form, 29 +/- 5% versus 6 +/- 2% and 5 +/- 3%, in groups 2 and 3, respectively. Nevertheless, neither cerebral blood flow (simil ar to 34 ml . 100 g(-1) . min(-1)) nor cerebral metabolic rate for oxy gen (similar to 1.2 ml O-2 . 100g(-1) . min(-1)) differed among groups . Conclusions: Because oxygen was equally available to the brain in al l groups, independent of whether oxygen was associated with erythrocyt es or not, it was concluded that erythrocyte/capillary interactions do not limit oxygen transfer from blood to brain during moderately hypot hermic CPB. The hypertensive response to alpha-alpha diaspirin cross-l inked hemoglobin during CPB is probably a result of nitric oxide scave nging.