Hematocrit Strategy in Infant Heart Surgery

BACKGROUND:

The optimal degree of hemodilution during profoundly hypothermic CPB remains controversial, and widely dissimilar hemodilution studies have evolved at centers that perform infant cardiac surgery. HCT, a measurement of the volume of red blood cells, is of interest in cardiopulmonary bypass. Higher HCT levels expose individuals to the risks of microvascular occlusion (blockage in the small blood vessels), while lower HCT levels may critically limit oxygen delivery to the brain and other organs. Preliminary research suggests that higher HCT levels provide superior brain and myocardial protection, but there have not been any studies that report on outcomes after usage of higher versus lower HCT levels.

DESIGN NARRATIVE:

In this single-center, prospective, randomized study, hemodilution to a HCT level of 35% versus 25% will be compared with respect to neurodevelopmental outcome and early postoperative course in infants with congenital heart disease. The first aim of this study will test the hypothesis that hemodilution to a HCT level of 35%, compared to a level of 25%, will be associated with superior central nervous system protection. The primary outcome variable will be developmental outcome at age 1 year, assessed using the Bayley Scales of Infant Development. Secondary outcome variables include the following: 1) tissue release of S-100 protein as a measure of cerebral cellular injury; 2) cerebral hemodynamics and oxygenation, determined by near infrared spectroscopy (NIRS); 3) intrinsic cerebral vasoregulation, measured by NIRS and transcranial Doppler; and 4) at age 1 year, neurologic examination, the MacArthur inventory, and structural and volumetric findings of magnetic resonance imaging (MRI).

The second aim of this study will test the hypothesis that hemodilution to a HCT level of 35%, compared to a level of 25%, will be associated with better early postoperative cardiovascular status. The primary outcome measure will be serum lactate levels 1 hour after the surgery. Secondary outcome measures will include the following: 1) the duration of postoperative endotracheal intubation, ICU stay, and hospital stay; 2) serum lactate levels; 3) the PaO2/FiO2 ratio; 4) levels of circulating pro-inflammatory cytokines; and 5) the percent change in total body water, estimated by bioelectrical impedance. The structure of the study will allow assessment of whether 1-year outcomes can be predicted by perioperative variables other than the HCT strategies. Through the use of novel techniques such as NIRS and volumetric MRI, the study may also provide insight into mechanisms by which HCT and other perioperative variables affect the brain. The information obtained from this study should be broadly generalized to infants with other forms of congenital heart disease undergoing early repair and should have substantial impact on clinical practice.