Diaspirin cross-linked hemoglobin does not increase brain oxygen consumption during hypothermic cardiopulmonary bypass in rabbits

Abstract

Background: Decreased erythrocyte deformability due to cardiopulmonary bypass (CPB) and/or hypothermia, may result in brain capillary beds that have decreased erythrocyte transit, resulting in a generalized impairment of brain oxygenation during CPB. Because brain capillary plasma flow continues even when erythrocyte flow is absent, the authors' hypothesized augmentation of plasma oxygen content with a non-erythrocyte-associated oxygen transport molecule would increase brain oxygen uptake during hypothermic CPB. Methods: Anesthetized New Zealand white rabbits, maintained on CPB at 27°C, were randomized to one of three groups. In group 1 (n = 13), plasma oxygen content was increased by administration of α-α diaspirin cross-linked hemoglobin. In this group, pretreatment with 0.5 mg/kg verapamil was necessary to prevent hypertension. In group 2 (n = 13), α-α diaspirin cross-linked hemoglobin was not administered, but verapamil was given as before (control). In group 3 (n = 13), neither α-α diaspirin cross-linked hemoglobin nor verapamil was administered (control). At 60 min of CPB, cerebral blood flow (microspheres) and cerebral metabolic rate for oxygen (Fick) were determined. Results: Systemic physiologic variables did not differ among groups. Although total arterial oxygen content was equivalent in all groups (~12.1 ml O2/dl), the α-α diaspirin cross-linked hemoglobin group had a much greater proportion of the total arterial oxygen content present in a non-erythrocyte-associated form, 29 ± 5% versus 6 ± 2% and 5 ± 3%, in groups 2 and 3, respectively. Nevertheless, neither cerebral blood flow (~34 ml · 100g-1 · min-1) nor cerebral metabolic rate for oxygen (~1.2 ml O2 · 100g-1 · min-1) differed among groups. Conclusions: Because oxygen was equally available to the brain in all groups, independent of whether oxygen was associated with erythrocytes or not, it was concluded that erythrocyte/capillary interactions do not limit oxygen transfer from blood to brain during moderately hypothermic CPB. The hypertensive response to α-α diaspirin cross-linked hemoglobin during CPB is probably a result of nitric oxide scavenging.