Comparison of Hematocrit Levels 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.

Inclusion Criteria:

- Undergoing repair of ventricular septal defect within 9 months of study entry

- Tetralogy of fallot

- D-transposition of the great arteries

- Atrio-ventricular septal defect

Exclusion Criteria:

- Birth weight less than 2.3 kg

- Recognizable phenotypic syndrome of congenital anomalies

- Extracardiac anomalies of greater than minor severity

- Previous cardiac surgery

- Associated cardiovascular anomalies requiring aortic arch reconstruction or
additional open surgical procedures before the planned developmental follow-up