Innovative Tests Monitor Brain Health During Pediatric Cardiac Surgery

Two new monitoring strategies could help detect and prevent brain damage in infants and children with congenital heart disease (CHD) undergoing surgery to repair their cardiac defects.

Researchers at Baylor college of Medicine (Houston, TX, USA) conducted a multicenter observational pilot study in 61 children (aged one week to 17 years) with CHD undergoing surgery, to evaluate the feasibility of two new brain-monitoring strategies. To do so, they developed the hemoglobin volume index (HVI), a noninvasive monitoring technique to assess changes in the brain arteries; this monitoring technique allowed them to determine the lowest pressure before automatic adjustment was compromised. The researchers also compared patient blood pressure changes with the blood levels of glial fibrillary acidic protein (GFAP), an indicator of brain damage.

The researchers found that a lower limit of pressure autoregulation (LLA) could be identified in 85% of the children and varied widely between patients, putting them at risk of brain hypoperfusion. Both the hemoglobin volume index and GFAP became abnormal when the childrens' heart and lung function was taken over by cardiopulmonary bypass during surgery, with the worst readings during rewarming, indicating that this was the period of highest risk for the child undergoing heart surgery. The researchers also found that the more time spent below LLA was associated with some increase in GFAP, suggesting a link between periods of decreased blood flow autoregulation and decreased brain blood flow and brain injury. The study was presented during the American Heart Association (AHA) Emerging Science Series, held during April 2012 in Dallas (TX, USA).

“Because the autoregulatory changes occurred almost concurrently with signs of brain injury, we may have a real-time measure where we can detect when injury is occurring and modify how we are managing the patients, for example being more aggressive with controlling blood pressure,” said lead author associate professor in anesthesiology and pediatrics Blaine Easley, MD.

Cerebral perfusion pressure (CPP) is the net pressure gradient causing brain perfusion. It must be maintained within narrow limits, because too little pressure could cause brain tissue to become ischemic, and too much could raise intracranial pressure (ICP). As a result, the body relies on autoregulation, an internal adaptive mechanism that works to mitigate response to stimuli. While most systems of the body show some degree of autoregulation, it is most clearly observed in the kidney, the heart, and the brain, which is very sensitive to overperfusion, and thus cerebral autoregulation plays an important role in maintaining an appropriate blood pressure.

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