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16727

Non-Invasive Autoregulation Monitoring In Neonatal Hypoxic Ischemic Encephalopathy

Friday, October 19, 2012
Room R02-R05 (Morial Convention Center)
Jessica A. Howlett, MD1, Frances J. Northington, MD1, Maureen M. Gilmore, MD1, Jacky M. Jennings, PhD, MPH2, Aylin Tekes, MD3, Thierry A. Huisman, MD3, Christoph U. Lehmann, MD1, Eric R. Jackson, MD4, Charlamaine Parkinson, RN1, Abby C. Larson, BS4, Jessica L. Jamrogowicz, BS4 and Jennifer K. Lee, MD4, (1)Neonatology, Johns Hopkins, Baltimore, MD, (2)General Pediatrics and Adolescent Medicine, Johns Hopkins, Baltimore, MD, (3)Pediatric Radiology, Johns Hopkins, Baltimore, MD, (4)Pediatric Anesthesiology and Critical Care Medicine, Johns Hopkins, Baltimore, MD

Purpose: Little is known about neonates’ optimal blood pressure. Even less is known about the blood pressure needed for neuroprotection following neonatal brain injury. Hypothermia affects cerebral autoregulation in neonatal piglet studies1 but neonates with hypoxic ischemic encephalopathy (HIE) undergoing hypothermia have not been studied.

Objective: We propose a novel method of autoregulation monitoring with near-infrared spectroscopy (NIRS) that can identify mean arterial blood pressure (MAP) ranges that optimally support autoregulation in neonates with HIE. Our hypothesis is that more time spent below the optimal MAP is associated with injury on brain MRI following HIE and treatment with hypothermia.

Methods: In an observational pilot study, term infants with HIE had arterial blood pressure and cerebral NIRS monitoring during therapeutic cooling, rewarming and normothermia. The autoregulation indices, cerebral oximetry index (COx) and hemoglobin volume index (HVx), are continuously calculated by a Pearson correlation coefficient between the MAP and NIRS data with laptop and ICM+ software. COx and HVx values range from -1 to +1, are negative/near-zero during functional autoregulation and become more positive with impaired autoregulation.1 The optimal MAP with most robust autoregulation was defined as the MAP bin with an identifiable nadir read independently by two separate physicians. After rewarming, Infants underwent brain MRIs.

Results: In eighteen HIE infants enrolled, cord blood gas pH was 6.99(+0.1) with base deficit of 11.8(+3.9).  Brain MRIs were obtained on day of life 9(+3). Abnormalities were found in fifteen infants (83%). The HVx-defined optimal MAP correlated with injury with greater time spent below optimal MAP during rewarming in five regions (Fig. 1). Associations with COx and MRI injury during rewarming were seen in the three regions (Fig. 2).  

Conclusion: Autoregulation can be continuously monitored with COx and HVx. Preliminary data shows that infants with more time below the optimal MAP, as defined by HVx, have evidence of MRI brain injury. The trend was less apparent with COx, which may be affected by tissue metabolism altered during hypothermia and rewarming. Future studies using HVx to target optimal MAPs to support autoregulation may improve neonatal outcomes.

References:

1. Lee JK, et al. Cerebral blood flow and cerebrovascular autoregulation in a swine model of pediatric cardiac arrest and hypothermia. Critical Care Medicine. 2011 Oct;39(10):2337-45.

Figure 1: HVx derived the optimal MAP was found in 12 neonates. Spending more time below optimal MAP had injury in the Central Gyrus, Basal Ganglia, Thalamus, White Matter and Brain Stem. No correlation found in the Posterior Limb of the Internal Capsule (PLIC).

Figure 2: Optimal MAP as defined by COx in 13 infants. More time spent below the optimal MAP was associated with injury in the Basal Ganglia, Thalamus, and Brain Stem.