Blood and brain tissue gaseous strategy for profoundly hypothermic total circulatory arrest

Brain tissue carbon dioxide tension, pH, and oxygen tension were measured in dogs undergoing hypothermic circulatory arrest below 20 degrees C with three types of blood gas manipulation. During core cooling, dogs were given pure oxygen (group I, n = 8), 5% carbon dioxide in oxygen (group II, n = 10), or 7% carbon dioxide in oxygen (group III, n = 4). During core cooling, brain tissue carbon dioxide tension decreased significantly in group I. During circulatory arrest, carbon dioxide tension rose by 21.5 mm Hg in group I, 35.3 mm Hg in group II, and 57.0 mm Hg in group III, nearly doubling in each group. From the last 5 minutes of core cooling to the end of rewarming, carbon dioxide tension was significantly higher in groups II and III than in group I. Brain tissue pH fell by 0.33 to 0.35 during 60 minutes of circulatory arrest and did not recover in groups II and III. Brain tissue oxygen tension decreased significantly during the latter two thirds of the circulatory arrest period in all three groups. To reduce progressive tissue hypercapnia and acidosis during and after circulatory arrest, a more hyperventilatory manipulation of blood gases than that achieved by alpha-stat strategy was thought beneficial for core-cooling perfusion.