Effects of oncotic pressure and hematocrit on outcome after hypothermic circulatory arrest

A recent study found that a higher-perfusate hematocrit was associated with improved neurologic recovery after deep hypothermic circulatory arrest. The current study examined the relative contributions of oxygen delivery and colloid oncotic pressure to this result, as well as the efficacy of different colloidal agents and modified ultrafiltration.

Twenty-six piglets were randomized into five groups (n = 5 or 6 animals per group): control group 1--blood and crystalloid prime, hematocrit of 20%; group 2--blood and hetastarch prime, hematocrit of 20%; group 3--blood and pentafraction prime, hematocrit of 20%; group 4--blood and crystalloid prime with 10 minutes of modified ultrafiltration; group 5--whole blood prime, hematocrit of 30%. All groups underwent 60 minutes of deep hypothermic circulatory arrest at 15 degrees C.

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 versus 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 recovery of phosphocreatine and intracellular acidosis, as measured by magnetic resonance spectroscopy, during rewarming than group 1 did (phosphocreatine, p = 0.0329; intracellular acidosis, p = 0.0462). Group 3 also showed accelerated recovery of intracellular acidosis (p = 0.0411). Cytochrome a,a3 recovery, determined by near-infrared spectroscopy, was significantly better in group 5 than in group 1 and worse in group 2 than in group 1 after rewarming. The neurologic deficit score and overall performance category score were best in group 5 (neurologic deficit score, p = 0.012; overall performance category score, p = 0.046) on the first postoperative day. Group 3 also had a better overall performance category score than group 1 did (p = 0.0068). Only group 1 and 2 animals showed histologic damage.

Both higher hematocrit and higher colloid oncotic pressure with pentafraction improve cerebral recovery after deep hypothermic circulatory arrest. The higher hematocrit improves cerebral oxygen delivery but does not reduce total body edema. Modified ultrafiltration after cardiopulmonary bypass is less effective than having a higher initial prime hematocrit or colloid oncotic pressure.