New test identified periods of impaired brain activity in children during cardiac surgery

Issue: June 2012

A new method involving dynamic hemoglobin volume index monitoring may provide early signs of brain injury in children undergoing cardiopulmonary bypass for congenital heart disease.

Perspective from John Murkin, MD

The brain can automatically adjust blood vessel size to maintain constant blood flow when BP changes, and time and absolute arterial BP below the lower limit of pressure autoregulation increases the brain’s risk for ischemia. Ronald B. Easley, MD, of the Baylor College of Medicine, and colleagues developed the hemoglobin volume index, a method of monitoring that uses near-infrared spectroscopy, to determine this lower limit.

To test the feasibility of the new test during cardiopulmonary bypass, researchers conducted a multicenter observational pilot study in which they compared patient BPs with blood levels of glial fibrillary acidic protein — an indicator of brain damage.

Researchers were able to identify the lower limit of pressure autoregulation in 85% of 61 children undergoing cardiopulmonary bypass to repair congenital heart disease. When the children’s heart and lung function were taken over by cardiopulmonary bypass during surgery, both the hemoglobin volume index and glial fibrillary acidic protein became abnormal, and researchers observed peaks during re-warming (P<.002), indicating the period of highest risk for children undergoing cardiac surgery. Study results also showed a trend toward increased glial fibrillary acidic protein with increased time below a lower limit of pressure autoregulation (P=.06). Researchers found no clinical strokes.

“[These results pose] the question: Does having a BP below a lower limit of autoregulation increase the risk of brain injury?” Easley said during the American Heart Association Emerging Science Series webinar. “We hope to address this question better in ongoing studies where we widen the period of our observation to the preoperative and postoperative periods.”

For more information:

Easley RB. Abstract #136. Presented at: the American Heart Association Emerging Science Series webinar; April 25, 2012.

Disclosure: Dr. Easley received a research grant from the American Heart Association.

Perspective

John Murkin, MD

A number of physicians have looked over the years at cerebral autoregulation intraoperatively at using xenon and transcranial Doppler, and they have been able to define cerebral autoregulation. What Easley and colleagues have done is to be able to move this beyond population dynamics and now be able to look individually at our management of patients. I think this a fundamentally different paradigm and interesting work.

John Murkin, MD

Professor of Anesthesiology

Schulich School of Medicine & Dentistry London, Ontario, Canada

Disclosures: Dr. Murkin received a research grant from PSI #11-41, honoraria from Covidien and is a consultant/advisory board member for Ornim Medical.