A comparison of complete blood replacement with varying hematocrit levels on neurological recovery in a porcine model of profound hypothermic (< 5 degrees C) circulatory arrest

Profound hypothermia (<5<degrees>C) may afford better neurological protecti on after circulatory arrest; however, there are the oretical concerns relat ed to microcirculatory sludging of blood components at these ultra-low temp eratures. We hypothesized that at temperatures <5<degrees>C, complete blood replacement results in superior neurological outcome. Twelve Yorkshire pig s (30 kg) underwent thoracotomy, cardiopulmonary bypass (CPB), and were ran domly assigned to one of three target hematocrits during circulatory arrest : 0%, 5%, 15%. Hextend(R) (6% hetastarch in a balanced electrolyte vehicle) was used for the CPB prime and as an exchange fluid. Animals were cooled t o a temperature <5<degrees>C, underwent l-h circulatory arrest, and were wa rmed to 35 degreesC with administsation of blood to increase the hematocrit to >25% before separation from CPB. The primary outcome,peak postoperative neurobehavioral score, was compared between groups. The 0% group (mean +/- so) had significantly (P < 0.02) better neurobehavioral scores than the 5% and 15% groups (6.0 +/- 2.9 vs 1.3 +/- 1.0 and 15 +/- 0.6)respectively. Ot her variables (e.g., intracranial pressure) were similar between groups. In a porcine model of profound hypothermia (<5 degreesC) and circulatory arre st, complete blood replacement resulted in superior neurological outcome Th is finding suggests that at ultralow temperatures, the presence of some blo od component (e.g., erythrocytes, leukocytes) may be deleterious.