Cerebral Blood Flow in Premature Infants

Abstract Background Hypercarbia increases cerebral blood flow secondary to cerebral vasodilatation, while hypocarbia can lead to vasoconstriction with a subsequent decrease in cerebral blood flow. The aim of this study was to examine CO2 cerebral vasoreactivity in a cohort of premature infants and to identify factors which influence this reactivity. Methods We prospectively studied a cohort of hemodynamically stable premature infants [birth weight (BW) <1500 g and gestational age (GA) ≤34 weeks]. Subjects underwent two studies, one in the first 72 h and the second after 1 week of life. Infants were continuously monitored via a physiology station that included transcutaneous CO2 (tcPCO2) monitor, near-infrared spectroscopy (NIRS), arterial pulse oximetry and heart rate. The total hemoglobin (Hb-T) signal of NIRS was used as an indicator of cerebral blood volume (CBV). Correlation between tcPCO2 and Hb-T was performed in each 1-h period using Pearson’s correlation. Factors affecting the CO2 cerebrovascular reactivity were examined using bivariate and linear regression analyses. Results A total of 3847 1-h epochs were obtained from 140 studies of 72 premature infants. tcPCO2 correlated positively with Hb-T in 42% of epochs. In regression analysis, factors associated with increased percentage of positive correlation epochs were male sex and younger postmenstrual age (PMA; β = 0.176, 0.169 and P-value = 0.036, 0.047 respectively). Factors associated with increased strength of positive correlation were mechanical ventilation and increased average tcPCO2 (β = 0.198, 0.220 and P-value = 0.024, 0.011 respectively). Conclusion Increased prematurity, male sex, mechanical ventilation and hypercarbia are associated with stronger PCO2 cerebrovascular reactivity in premature infants. This association may explain their role in the pathogenesis of brain injury.

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Abstract TP400: Evoked Functional Cerebral Hemodynamic and Metabolic Responses in Premature Infants with and without Germinal Matrix Hemorrhage

Stroke ◽

10.1161/str.48.suppl_1.tp400 ◽

2017 ◽

Vol 48 (suppl_1) ◽

Author(s):

Pei-Yi Lin ◽

Fang-Yu Cheng ◽

Katherine Hagan ◽

Yvonne Sheldon ◽

Ellen P. Grant ◽

...

Keyword(s):

Blood Flow ◽

Cerebral Blood Flow ◽

Premature Infants ◽

Neonatal Intensive Care ◽

Near Infrared ◽

Continuous Wave ◽

Oxygen Metabolism ◽

Correlation Spectroscopy ◽

Germinal Matrix ◽

Germinal Matrix Hemorrhage

We have created an innovative new method which uses frequency domain near-infrared spectroscopy (FDNIRS) in combination with diffuse correlation spectroscopy (DCS) to quantitatively measure cerebral blood flow (CBF) and oxygen metabolism (CMRO 2 ) right at the infant’s bedside. We have previously found CBF and CMRO 2 are more sensitive indicators of cerebral pathophysiology than hemoglobin saturation (SO 2 ). Using FDNIRS-DCS, we had found extremely premature infants with germinal matrix hemorrhage (GMH) have lower cerebral blood flow (CBF) and oxygen metabolism (CMRO 2 ) than gestational age-matched controls. For this study, we investigate whether GMH, along with age and hematocrit levels, affect evoked hemodynamic responses. The study protocol was reviewed and approved by the Institutional Review Board for Partners Healthcare. We enrolled eleven premature infants in the neonatal intensive care unit at Brigham and Women’s Hospital. Three of them had Grade I GMH diagnosed by head ultrasound on the first three days of life. We integrated continuous wave NIRS (CWNIRS) with DCS to measure dynamic changes of cerebral hemoglobin concentrations (HbO) and CBF in response to somatosensory stimuli. For each measurement, we measured differential path length factors and baseline cerebral hemoglobin concentrations with FDNIRS to quantify relative hemodynamic and metabolic changes (rHbO, rCBF and rCMRO 2 ) in response to tactile stimulation. We observed a faster response time to reach peak value in preterm infants with increasing postmenstrual age (PMA), demonstrating the response matures with age to become more adult-like (r=-0.513, p=0.007). In addition, infants measured at older PMA tend to have responses with a larger undershoot in HbO. However, the HbO undershoot did not translate into an undershoot in CMRO 2 . The HbO undershoot may therefore be a consequence of low hematocrit during the first two months of life which results in insufficient oxygen supply and leads to abnormally large oxygen extraction from the blood. We found the activation pattern of Grade I GMH infants did not differ from premature infants without hemorrhage. The study is ongoing and shows our method is suitable to measure cerebral maturation in neonates with hemorrhage.

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