Hemoglobin volume index helps monitor children during heart repair operations
A newly developed monitoring test may provide surgeons with real time data about a child’s brain health during heart surgery to repair congenital defects.
The new tool is significant because brain injury occurs in 30 percent to 70 percent of children undergoing procedures to repair congenital heart defects such as valve abnormalities.
Previously there was no method for detecting brain injuries as they occurred during operations.
R. Blaine Easley, MD, lead author and associate professor in anesthesiology and pediatrics at Baylor college of Medicine in Houston, led the test development. It requires only a small amount of blood to detect injury to brain tissue.
A second autoregulation monitoring test also was developed to non-invasively monitor children during surgery when blood flow to the brain may be low.
Dr. Easley said that because they found that autoregulatory changes occurred almost concurrently with signs of brain injury, they were able to develop a real-time monitoring system where such injuries can be detected as they happen.
This would allow doctors to modify patient management, such as more aggressively controlling blood pressure.
During the multi-center observational pilot study of high-risk children with congenital heart disease, investigators developed the “hemoglobin volume index,” a non-invasive monitoring technique capable of detecting changes in brain arteries.
These changes could indicate the brain is not receiving enough blood.
The brain automatically adjusts blood vessel size to ensure constant blood flow with blood pressure changes so they used the technique to determine the lowest blood pressure that occurred before that automatic adjustment was compromised. They then compared patient blood pressures with blood levels of glial fibrillary acidic protein (GFAP), an indicator of brain damage.
Researchers found that in 61 children between the ages of 1 and 17 who underwent heart repair surgery both the hemoglobin volume index and GFAP became abnormal when a heart and lung machine took over function during bypass operations. The worst readings were recorded during rewarming, the highest risk period for the child.
Investigators also found that a lower limit of pressure autoregulation was identified in 85 percent of children, though it varied between patients. These patients were considered at risk of decreased brain blood flow.
Most significantly, researchers discovered that longer periods of time in which a patient maintained a lower limit of pressure autoregulation were linked with an increase in GFAP. This suggested the link between periods of decreased blood flow autoregulation and decreased brain blood flow, and brain injury.
Investigators are planning a multi-center study to examine procedure test results, MRI changes and neurodevelopmental outcomes 18 months after surgery.
The study, funded in part by an American Heart Association clinical research program grant from the Southwest affiliate, was presented today during the American Heart Association’s Emerging Science Series webinar..