EFFECTS OF ONCOTIC PRESSURE AND HEMATOCRIT ON OUTCOME AFTER HYPOTHERMIC CIRCULATORY ARREST

Background. A recent study found that a higher-perfusate hematocrit wa s associated with improved neurologic recovery after deep hypothermic circulatory arrest. The current study examined the relative contributi ons of oxygen delivery and colloid oncotic pressure to this result, as well as the efficacy of different colloidal agents and modified ultra filtration. Methods. Twenty-six piglets were randomized into five grou ps (n = 5 or 6 animals per group): control group 1-blood and crystallo id prime, hematocrit of 20%; group 2-blood and hetastarch prime, hemat ocrit of 20%; group 3-blood and pentafraction prime, hematocrit of 20% ; group 4-blood and crystalloid prime with 10 minutes of modified ultr afiltration; group 5-whole blood prime, hematocrit of 30%. All groups underwent 60 minutes of deep hypothermic circulatory arrest at 15 degr ees C. Results. Groups 2 and 3 showed less body weight gain (analysis of variance, p = 0.001; group 2 versus group 1, p = 0.0009; group 3 ve rsus group 1, p = 0.0009) and body water content after cardiopulmonary bypass (analysis of variance, p = 0.001; group 2 versus group 1, p = 0.003; group 3 versus group 1, p = 0.013). Group 5 showed more rapid r ecovery of phosphocreatine and intracellular acidosis, as measured by magnetic resonance spectroscopy, during rewarming than group 1 did (ph osphocreatine, p = 0.0329; intracellular acidosis, p = 0.0462). Group 3 also showed accelerated recovery of intracellular acidosis (p = 0.04 11). Cytochrome a,a3 recovery, determined by near-infrared spectroscop y, was significantly better in group 5 than in group 1 and worse in gr oup 2 than in group 1 after rewarming. The neurologic deficit score an d overall performance category score were best in group 5 (neurologic deficit score, p = 0.012; overall performance category score, p = 0.04 6) on the first postoperative day. Group 3 also had a better overall p erformance category score than group 1 did (p = 0.0068). Only group 1 and 2 animals showed histologic damage. Conclusions. Both higher hemat ocrit and higher colloid oncotic pressure with pentafraction improve c erebral recovery after deep hypothermic circulatory arrest. The higher hematocrit improves cerebral oxygen delivery but does not reduce tota l body edema. Modified ultrafiltration after cardiopulmonary bypass is less effective than having a higher initial prime hematocrit or collo id oncotic pressure. (C) 1998 by The Society of Thoracic Surgeons.