The influence of hemodilution on outcome after hypothermic cardiopulmonary bypass: Results of a randomized trial in infants

Background: We hypothesized that cognitive impairment and hemodynamic instability after infant cardiac surgery with cardiopulmonary bypass might be exacerbated by hemodilution. Methods: In a single-center randomized trial with blinded assessment of outcomes, we compared use of 2 hemodilution protocols during hypothermic cardiopulmonary bypass with infant cardiac surgery. The primary perioperative end point was lowest cardiac index in the first 24 hours postoperatively, and primary end points at age I year were scores on the Psychomotor Development Index and Mental Developmental Index of the Bayley Scales. Results: Among 147 subjects, 74 were assigned to the lower-hematocrit strategy (21.5% +/- 2.9%, mean +/- SD at onset of low-flow bypass) and 73 to the higher-hematocrit strategy (27.8% +/- 3.2%). In intent-to-treat analyses the lower-hematocrit group had lower nadirs of cardiac index (P=.02), higher serum lactate levels 60 minutes after cardiopulmonary bypass (P=.03), and a greater percentage increase in total body water on the first postoperative day (P =.006). Blood product use and adverse events were similar in the 2 groups. At age I year (113 children), the lower-hematocrit group had worse scores on the Psychomotor Development Index (81.9 +/- 15.7 vs 89.7 +/- 14.7, P =.008), as well as more Psychomotor Development Index scores at least 2 SDs below the population mean (16/56 [29%] vs 5/53 [9%], P =.01). The groups had similar Mental Developmental Index scores and findings on neurologic examination. Inferences using hematocrit as a continuous variable were similar to those based on intent-to-treat analyses. Conclusions: Hemodilution to a hematocrit level in wide use for cardiopulmonary bypass and thought to be safe is associated with adverse perioperative and developmental outcomes in infants.