EFFECT OF HEMOGLOBIN CONCENTRATION ON OXYHEMOGLOBIN DISSOCIATION DURING HYPOTHERMIC BLOOD CARDIOPLEGIC ARREST

Background: This study compares oxyhemoglobin dissociation during the nonperfused periods of hypothermic cardioplegic arrest in two blood ca rdioplegic solutions with different hemoglobin concentrations. The hyp othesis is that more oxygen will dissociate from hemoglobin in a blood cardioplegic solution with a higher hemoglobin content than from a ca rdioplegic solution with a lower hemoglobin content. However, the incr ement in the volume of oxygen that dissociates from hemoglobin will be less than anticipated by a ratio of hemoglobin concentrations in the cardioplegic solution. Methods and results: Pigs (n = 22) were support ed by bypass and subjected to 60 minutes of hypothermic cardioplegic a rrest with either a high-hemoglobin (n = 10) or low-hemoglobin (n = 12 ) blood cardioplegic solution. Aortic root and coronary sinus blood sa mples were obtained before bypass and 5 seconds after the start of car dioplegic infusions at 20, 40, and 60 minutes of cardioplegic arrest, Oxyhemoglobin dissociation occurred in both experimental groups during the ischemic intervals of cardioplegic arrest. However, there were no significant differences between the high- and low-hemoglobin groups i n the arterial-venous oxygen content differences for samples taken aft er each of the three ischemic intervals (p values: control = 0.78; car dioplegia interval 1 = 0.95; interval 2 = 0.56; and interval 3 = 0.12) . Conclusions: The present study emphasizes the inherent limitations o f unmodified erythrocyte hemoglobin as an oxygen source in hypothermic alkalotic cardioplegic solutions. These limitations may be obviated b y methods that increase the dissolved oxygen content of the cardiopleg ic solution or methods that decrease the affinity of hemoglobin for ox ygen under conditions of hypothermia and alkalosis.