Higher hematocrit improves cerebral outcome after deep hypothermic circulatory arrest

Abstract

Background: Various degrees of hemodilution are currently in clinical use during deep hypothermic circulatory arrest to counteract deleterious rheologic effects linked with brain injury by previous reports. Material and methods: Seventeen piglets were randomly assigned to three Groups. Group I piglets (n = 7) received colloid and crystalloid prime (hematocrit < 10%), group II piglets (n = 5) received blood and crystalloid prime (hematocrit 20%), group III piglets (n = 5) received blood prime (hematocrit 30%). All Groups underwent 60 minutes of deep hypothermic circulatory arrest at 15° C, with continuous magnetic resonance spectroscopy and near-infrared spectroscopy Neurologic recovery was evaluated for 4 days (neurologic deficit score 0, normal, to 500, brain death; overall performance category 1, normal, to 5, brain death). Neurohistologic score (0, normal, to 5+, necrosis) was assessed after the animals were euthanized on day 4. Results: Group I had significant loss of phosphocreatine and intracellular acidosis durinG early cooling (phosphocreatine in group I, 86.3% ± 26.8%; group II, 117.3% ± 8.6%; group III, 110.9% ± 2.68%;p = 0.0008; intracellular pH in Group I, 6.95 ± 0.18: group II, 7.28 ± 0.04; group III, 7.49 ± 0.04; p = 0.0048). Final recovery was the same fur all groups. Cytochrome aa3 was inure reduced in group I during deep hypothermic circulatory arrest than in either of the other Groups (group I, -43.6 ± 2.6; group II, -16.0 ± 5.2; group III, 1.3 ± 3.1: p < 0.0001). Neurologic deficit score was best preserved in group III (p < 0.05 group II vs group III) on the first postoperative day, although this difference diminished with time and all animals were neurologically normal after 4 days. Histologic assessment was worst among group I in neocortex area (Group I, 1.33 ± 0.3; group II, 0.22 ± 0.1; group III, 0.40 ± 0.2, p < 0.05, group I vs group II;p = 0.0287, group I vs group III). Conclusion: Extreme hemodilution during cardiopulmonary bypass may cause inadequate oxygen delivery durinG early cooling. The higher hematocrit with a blood prime is associated with improved cerebral recovery after deep hypothermic circulatory arrest.