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We appreciate the thoughtful comments and questions by Ghimire (1) on our recently published article (2) in Pediatric Critical Care Medicine. In our study, we sought to analyze the relationship of cerebral tissue oxygenation index (cTOI) variability, as measured by near-infrared spectroscopy, with neurodevelopmental outcome in survivors of surgery for congenital heart disease. After controlling for three well-established factors associated with neurodevelopmental outcome—single ventricle physiology, defects with aortic obstruction, and duration of deep hypothermic circulatory arrest—we found that patients with decreased cTOI variability following surgery were at increased risk of poor neurodevelopmental outcome.
As Ghimire (1) points out, there are additional risk factors for poor neurodevelopmental outcome for which we did not control for in our study. Among patients with d-transposition of the great arteries, 82% underwent balloon atrial septostomy with no differences in neurodevelopmental outcome or cTOI variability between those who did and did not undergo that procedure. Three patients (7%) in our cohort had postoperative seizures. There were no differences in neurodevelopmental outcome or cTOI variability based on seizure activity. It should be noted that during the period of study, universal electroencephalogram monitoring in the postoperative period at the study institution was not routine, thus our findings are largely limited only to clinically apparent seizures. The relationship between cTOI variability and seizure activity, both clinical and subclinical, warrants further study.
Finally, among the 57% of our cohort that underwent neuroimaging studies, stratified analyses by diagnosis classification yielded no relationships between abnormalities found on clinical neuroimaging studies and neurodevelopmental outcome or cTOI variability. More specialized neuroimaging using advanced MRI technology may identify features associated with cTOI variability and neurodevelopmental outcomes, and it is our intent to include this in future studies.

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