Postnatal adaptation of brain circulation in preterm infants

Analysis of cranial ultrasound images for newborn

Introduction

Neonatal cranial ultrasound plays an important role in the evaluation of neonatal brain development and related diseases.

Methods

This paper preliminarily explored the analysis and interpretation methods of neonatal brain ultrasound images, and applied the relevant medical image analysis methods to analyze the relevant neonatal brain ultrasound images in more detail.

Results

Compared with other types of imaging methods, ultrasound has its unique advantages and characteristics in such applications as neonatal head imaging.

Discussion

The analysis steps and schemes adopted in this paper have certain reference significance for the analysis of other neonatal brain pictures.

Early arterial pressure monitoring and term-equivalent age MRI findings in very preterm infants

INTRODUCTION

Variability of arterial blood pressure (ABP) has been associated with intraventricular hemorrhage in very preterm neonates (VPT) and may predict other brain lesions assessed at term-equivalent of age (TEA).

METHODS

This was a prospective single-center study including VPT with early invasive continuous ABP monitoring and assessed at TEA using brain magnetic resonance imaging (TEA-MRI). The association between early mean ABP (MABP) and TEA-MRI findings was modeled by multivariate logistic regression analysis using covariates selected by the LASSO method.

RESULTS

Among 99 VPT, the LASSO procedure selected consecutive periods of lowest MABP of 30 min on day 1 (d1) and 10 min on day 2 (d2) as the most relevant durations to predict TEA-MRI findings (OR [95% CI], 1.11 [1.02-1.23], p = 0.03 and 1.13 [1.01-1.27], p = 0.03, respectively). ROC curve analysis showed optimal thresholds at 30.25 mmHg on d1 and 33.25 mmHg on d2. This significant association persisted after adjustment with covariates including birthweight, gestational age, sex, and inotrope exposure. Final models selected by LASSO included the decile of the birthweight and lowest MABP for 30 min on d1 and 10 min on d2, for which the areas under the ROC curve were 74% and 75%, respectively.

CONCLUSION

Early continuous ABP monitoring may predict brain TEA-MRI findings in VPT.

IMPACT

Early arterial blood pressure monitoring may contribute to predicting brain damage upon MRI at term-equivalent of age for infants born very preterm. Careful blood pressure continuous monitoring in very preterm infants may identify infants at risk of long-term brain damage. Umbilical artery catheterization provides the best option for continuously monitoring arterial blood pressure in very preterm infants.

Cerebral neurovascular embryology, anatomic variations, and congenital brain arteriovenous lesions

Cerebral neurovascular development is a complex and coordinated process driven by the changing spatial and temporal metabolic demands of the developing brain. Familiarity with the process is helpful in understanding neurovascular anatomic variants and congenital arteriovenous shunting lesions encountered in endovascular neuroradiological practice. Herein, the processes of vasculogenesis and angiogenesis are reviewed, followed by examination of the morphogenesis of the cerebral arterial and venous systems. Common arterial anatomic variants are reviewed with an emphasis on their development. Finally, endothelial genetic mutations affecting angiogenesis are examined to consider their probable role in the development of three types of congenital brain arteriovenous fistulas: vein of Galen malformations, pial arteriovenous fistulas, and dural sinus malformations.

Cerebral Hemodynamics Are Not Affected by the Size of the Patent Ductus Arteriosus

INTRODUCTION

Although patent ductus arteriosus (PDA) has been implicated to play a role in the development of cerebral ischemia and intraventricular hemorrhage (IVH) through a cerebral steal phenomenon, there is conflicting data on the impact of PDA size on cerebral blood flow (CBF). Cerebral autoregulation is the brain's innate protective mechanism to maintain constant CBF despite changes in blood pressure, and it is unclear if it is influenced by PDA hemodynamics.

OBJECTIVE

To delineate the relationship between PDA size and CBF velocity (CBFv) in premature infants.

METHODS

113 premature infants born at 23-29 weeks' gestation had echocardiograms performed during the first week after birth to evaluate for PDA. The infants were divided into 3 groups according to PDA size: none-to-small, moderate, or large. All infants had continuous recordings of umbilical artery blood pressure (ABP) and CBFv during the first week after birth. Critical closing pressure (CrCP) was calculated from ABP and CBFv tracings. Diastolic closing margin (DCM), defined as diastolic blood pressure minus CrCP, was calculated as a marker for the risk of developing IVH.

RESULTS

Infants with a large PDA (n = 16) had the lowest ABP across all phases of the cardiac cycle (systole [p = 0.003], mean [p = 0.005], and diastole [p = 0.012]) compared to infants with a moderate (n = 19) or none-to-small PDA (n = 78). Despite blood pressure being different, systolic, mean, and diastolic CBFv were not different across groups. Cerebral autoregulation, as measured during systole, was intact regardless of the PDA size. CrCP and DCM were also not different across groups.

CONCLUSIONS

In this cohort, CBFv and cerebral autoregulation during systole were not influenced by PDA size. Intact cerebral autoregulation may play a role in maintaining CBFv regardless of PDA size and differences in ABP.

A theory for polymicrogyria and brain arteriovenous malformations in HHT

Hereditary hemorrhagic telangiectasia (HHT) is generally considered a disorder of endothelial dysfunction, characterized by the development of multiple systemic arteriovenous malformations (AVMs), including within the brain. However, there have recently been a number of reports correlating HHT with malformations of cortical development, of which polymicrogyria is the most common type. Here we present 7 new cases demonstrating polymicrogyria in HHT, 6 of which demonstrate a brain AVM (bAVM) in close spatial proximity, with the aim of providing a common origin for the association. Upon reviewing patient genetics and imaging data and comparing with previously reported findings, we form 2 new conclusions: (1) polymicrogyria in HHT appears exclusively associated with a subset of mutations in the transmembrane protein endoglin that is involved with blood flow-related mechanotransduction signaling during angiogenesis and (2) the polymicrogyria is characteristically unilateral, typically focal, and correlates with vascular regions experiencing low fluid shear stress during corticogenesis in utero. Integrating these with findings in the literature from genetics and molecular biology experiments, we propose a theory suggesting haploinsufficient endoglin mutations, especially those that are dominant-negative, may predispose focal, aberrant hypersprouting angiogenesis during corticogenesis that leads to the production of polymicrogyria. This hypoxic insult may further serve as the revealing trigger for later development of a spatially coincident bAVM. This hypothesis suggests an essential role for endoglin-mediated hemodynamic mechanotransduction in normal corticogenesis.

Temporal evolution of quantitative EEG within 3 days of birth in early preterm infants

For the premature newborn, little is known about changes in brain activity during transition to extra-uterine life. We aim to quantify these changes in relation to the longer-term maturation of the developing brain. We analysed EEG for up to 72 hours after birth from 28 infants born <32 weeks of gestation. These infants had favourable neurodevelopment at 2 years of age and were without significant neurological compromise at time of EEG monitoring. Quantitative EEG was generated using features representing EEG power, discontinuity, spectral distribution, and inter-hemispheric connectivity. We found rapid changes in cortical activity over the 3 days distinct from slower changes associated with gestational age: for many features, evolution over 1 day after birth is equivalent to approximately 1 to 2.5 weeks of maturation. Considerable changes in the EEG immediately after birth implies that postnatal adaption significantly influences cerebral activity for early preterm infants. Postnatal age, in addition to gestational age, should be considered when analysing preterm EEG within the first few days after birth.

Circulatory Changes and Cerebral Blood Flow and Oxygenation During Transition in Newborns With Congenital Heart Disease

This review aims to describe how the complex events of cardiovascular transition may affect the brain of infants with congenital heart disease (CHD). In particular, we describe the vulnerabilities of the neonatal brain in the transitional period during and immediately after delivery and propose management strategies that can potentially influence neurodevelopmental outcomes in this patient population. Delayed brain development has been identified in the third trimester fetus with certain forms of CHD. Neonates with critical CHD are at risk for brain injury even before their neonatal operation. The transitional period from fetal to neonatal life is marked with hemodynamic changes that can affect cerebral blood flow and oxygenation and may exacerbate injury and influence outcome. We propose specific perinatal management strategies tailored to maternal-fetal pairs aimed at optimizing hemodynamic stability, especially cerebral blood flow and oxygenation, to maximize the neurodevelopmental potential of infants with CHD.

The Ontogeny of Cerebrovascular Critical Closing Pressure

Premature infants are at risk of vascular neurological insults. Hypotension and hypertension are considered injurious, but neither condition is defined with consensus. Critical closing pressure (CrCP) is the arterial blood pressure (ABP) at which cerebral blood flow ceases. CrCP may serve to define subject-specific low or high ABP. Our objective was to quantify CrCP as a function of gestational age (GA). One hundred eighty-six premature infants with a GA range of 23-33 weeks, were monitored with umbilical artery catheters and transcranial Doppler insonation of middle cerebral artery flow velocity (FV) for 1-h sessions over the first week of life. CrCP was calculated using an impedance model derivation with Doppler-based estimations of cerebrovascular resistance and compliance. CrCP increased significantly with GA (r = 0.47; slope = 1.4 mmHg/week gestation), an association that persisted with multivariate analysis (p < 0.001). Higher diastolic ABP and higher GA were associated with increased CrCP (p <0.001 for both). CrCP increases significantly at the end of the second and beginning of the third trimester. The low CrCP observed in premature infants may explain their ability to tolerate low ABP without global cerebral infarct or hemorrhage.

Can the Assessment of Spontaneous Oscillations by Near Infrared Spectrophotometry Predict Neurological Outcome of Preterm Infants?

The aim was to assess the correlation between cerebral autoregulation and outcome. Included were 31 preterm infants, gestational age 26 1/7 to 32 2/7 and <24 h life. Coherence between cerebral total haemoglobin (tHb) or oxygenation index (OI) measured by near-infrared spectrophotometry (NIRS) and systemic heart rate (HR) or arterial blood pressure (MAP) was calculated as a measure of autoregulation. In contrast to previous studies, low coherences in the first 24 h were significantly associated with intraventricular haemorrhage, death or abnormal neurodevelopmental outcome at 18 months or later. We suggest that our results can be explained by the concept of a multi-oscillatory-functions-order.

MR assessment of pediatric hydrocephalus: a road map

PURPOSE

This study was conducted to design a rational approach to the MR diagnosis of hydrocephalus based on a pathophysiologic reevaluation of its possible mechanisms and to apply it to the different etiological contexts.

METHOD

A review of the literature reports describing new physiologic models of production and absorption and of the hydrodynamics of the CSF was made.

RESULTS

Besides the secretion of CSF by the choroid plexuses, and its passive, pressure-dependent transdural absorption (arachnoid villi, dural clefts, cranial, and spinal nerve sheaths), water transporters, aquaporins, allow water (if not ions and organic molecules) to exchange freely between the brain parenchyma and the CSF spaces across the ependymal and the pial interfaces (including the Virchow-Robin spaces). Consequently, the CSF bulk flow is not necessarily global, and situations of balanced absorption-secretion may occur separately in different CSF compartments such as the ventricular, intracranial, or intraspinal CSF spaces. This means that rather than from a hypothetical pressure gradient from the plexuses to the dural sinuses, the dynamics of the CSF depend on the force provided in those different compartments by the arterial systolic pulsation of the pericerebral (mostly), intracerebral, and intraventricular (choroid plexuses) vascular beds.

CONCLUSION

Using MR imaging, diverse varieties of hydrocephalus may tentatively be explained by applying those concepts to the correspondingly diverse causal diseases. Hopefully, this may have an impact on the choice of the treatment strategies also.

Randomized, Placebo-Controlled Trial of Dobutamine for Low Superior Vena Cava Flow in Infants

OBJECTIVE

To gather information for a future confirmatory trial of dobutamine (DB) for circulatory impairment (ie, low superior vena cava [SVC] flow).

STUDY DESIGN

A total of 127 infants born at < 31 weeks gestational age were serially scanned from birth to 96 hours after birth. The infants were randomly assigned to 2 groups and were treated with DB (stepwise dose increase, 5-10-15-20 μg/kg/min) or placebo if they had an SVC flow < 41 mL/kg/min within the first 24 hours after birth. The primary outcome measures were the achievement and maintenance of an SVC flow ≥ 41 mL/kg/min. Secondary outcome measures were the short-term evolution of clinical and biochemical variables, near-infrared spectroscopy, cranial Doppler ultrasound, and clinical outcomes.

RESULTS

SVC flow increased throughout the first 96 hours for the entire cohort. All of the randomized infants (n = 28) except 2 achieved and maintained an SVC flow ≥ 41 mL/kg/min after intervention; however, the infants treated with DB (n = 16) showed a higher heart rate and improved base excess compared with those treated with placebo (n = 12). Low SVC flow was associated with low gestational age (P = .02) and poor condition at birth (P = .02). Low SVC flow significantly increased the risk of severe ischemic events (OR, 13; 95% CI, 2.4-69.2; P < .01).

CONCLUSION

This exploratory trial demonstrates a tendency toward improved short-term clinical and biochemical perfusion variable outcomes in infants with low SVC flow treated with DB.

TRIAL REGISTRATION

ClinicalTrials.gov (NCT01605279) and the European Clinical Trials Database (EurodraCT 2009-010901-35).

Ontogeny of cerebrovascular critical closing pressure

BACKGROUND

Premature infants are at risk of vascular neurologic insults. Hypotension and hypertension are considered injurious, but neither condition is defined with consensus. Cerebrovascular critical closing pressure (CrCP) is the arterial blood pressure (ABP) at which cerebral blood flow (CBF) ceases. CrCP may serve to define subject-specific low or high ABP. Our objective was to determine the ontogeny of CrCP.

METHODS

Premature infants (n = 179) with gestational age (GA) from 23-31 wk had recordings of ABP and middle cerebral artery flow velocity twice daily for 3 d and then daily for the duration of the first week of life. All infants received mechanical ventilation. CrCP was calculated using an impedance-model derivation with Doppler-based estimations of cerebrovascular resistance and compliance. The association between GA and CrCP was determined in a multivariate analysis.

RESULTS

The median (interquartile range) CrCP for the cohort was 22 mm Hg (19-25 mm Hg). CrCP increased significantly with GA (r = 0.6; slope = 1.4 mm Hg/wk gestation), an association that persisted with multivariate analysis (P < 0.0001).

CONCLUSION

CrCP increased significantly from 23 to 31 wk gestation. The low CrCP observed in very premature infants may explain their ability to tolerate low ABP without global cerebral infarct or hemorrhage.

Superior vena cava flow and intraventricular haemorrhage in extremely preterm infants

OBJECTIVE

To evaluate the relationship between superior vena cava flow (SVCF) measurements within the first 24 h of life, and development of intraventricular haemorrhage (IVH) in extremely preterm infants.

STUDY DESIGN

Single centre retrospective cohort study of 108 preterm infants born less than 28 weeks' gestation. Main outcome measure was degree of IVH at day 7 postnatal age.

RESULTS

The mean GA of the study group was 25.4 weeks. Mean SVCF was lower (75 ml/kg/min) in infants later diagnosed with IVH (n = 46) compared to infants, who did not develop IVH (87.7 ml/kg/min, p = 0.055). PDA diameter was inversely associated with SVCF (p = 0.024) and reversal of flow in the descending aorta (p = 0.001). Sensitivity analysis did not confirm an independent association of SVCF with development of IVH [OR 0.990 (0.978-1.002), p = 0.115].

CONCLUSION

Our study describes early SVCF in extremely preterm infants is associated with the extent of ductal shunting, but insensitive in predicting IVH.

Insights into cerebrospinal fluid and cerebral blood flows in infants and young children

This study investigates the craniospinal flows of blood and cerebrospinal fluid using phase-contrast magnetic resonance imaging (MRI) on 23 control neonates and infants (5 d-68 mo old). Mean arterial cerebral blood flow increased with age of infant from 180 mL/min after birth to 1330 mL/min around 6 years of age. This corresponds to 51 mL/min/100 g and 95 mL/min/100 g, respectively. Cervical cerebrospinal fluid stroke volume increased from 38 × 10(-3) mL to 752 × 10(-3) mL per cardiac cycle. After arterial systolic blood inflow, we observed a delay of the venous outflow that was always preceded by cerebrospinal fluid flushing out through the spinal canal. These results highlighted the importance of compliance of the spinal compartment and the interaction of blood and cerebrospinal fluid dynamics. The capacity of the spinal compartment to receive intracranial cerebrospinal fluid in presence of fontanels was demonstrated. We provide reference values to understand the physiology of cerebrospinal fluid and cerebral blood.

Effect of oxygen inhalation on cerebral blood flow velocity in premature neonates

BACKGROUND

The study tested the hypothesis that hyperoxemia and hypoxemia differentially alter cerebral blood flow velocity (CBFV) in a gestational age-dependent manner.

METHODS

Cases comprised 98 neonates with mild respiratory distress, receiving oxygen for >24 h in first 48 h of life. Ninety-eight age- and-weight-matched healthy neonates served as controls. Infants with perinatal asphyxia, shock, sepsis, malformations, acidosis/alkalosis, and hypo/hypercarbia were excluded. Resistance index (RI), pulsatility index (PI), peak systolic flow velocity (PSV), and vascular diameter were measured in internal carotid, vertebral, and middle cerebral arteries by transcranial doppler ultrasonography between 24 and 48 h of life with immediate postdoppler arterial blood gas analysis. For subgroup analysis, neonates were divided by gestational age and PaO2.

RESULTS

An overall decrease in RI/PI and increase in PSV and vasodilation was observed in cases. Hyperoxemia (PaO2 >90 mm Hg) was more common in premature neonates. Neonates <32 wk showed an increase in CBFV (decreased RI/PI and increased PSV/diameter) in association with hyperoxemia. An opposite response was observed in neonates ≥ 32 wk, where CBFV increased in response to hypoxemia (PaO2 <50 mm Hg) and decreased in hyperoxemia. Increased CBFV showed high predictive accuracy for immediate mortality and intracranial hemorrhage.

CONCLUSION

Depending on gestational maturity, hyperoxemia or hypoxemia produce differential effects in CBFV.

Observational study of cerebral hemodynamics during dopamine treatment in hypotensive ELBW infants on the first day of life

OBJECTIVE

To evaluate cerebral hemodynamics during dopamine treatment in hypotensive (mean arterial blood pressure (MABP)<gestational age) extremely low birth weight (ELBW) infants.

STUDY DESIGN

Continuous monitoring of cerebral blood flow velocity (CBFv), MABP and PCO2 was performed in hypotensive ELBW infants on the first day of life, beginning with an ∼15-min baseline reading and continued during advancing dopamine infusion until MABP was optimized. Physiological variables and CBFv reactivity were compared before and after MABP was optimized.

RESULT

Fifteen hypotensive ELBW infants (625±174 g; 24 (23 to 24.8) weeks) were studied. Mean CBFv increased from 10.9±3.7 to 15.7±5.7 cm s(-1) (P=0.001) simultaneously as MABP increased from 22.3±2.8 to 35.2±9.7 mm Hg (P<0.001). Mean CBFv reactivity (95% confidence interval (CI)) was 3.9 (1.6 to 6.2) %mm Hg(-1). Nine infants died and/or developed severe intraventricular hemorrhage (IVH).

CONCLUSION

Mean CBFv increased pressure-passively as MABP was optimized by dopamine treatment in very sick hypotensive ELBW infants on the first day of life.

Calibration of a prototype NIRS oximeter against two commercial devices on a blood-lipid phantom

In a blood-lipid liquid phantom the prototype near-infrared spectroscopy oximeter OxyPrem was calibrated against the INVOS® 5100c adult sensor in respect to values of regional tissue oxygen haemoglobin saturation (rStO2) for possible inclusion in the randomised clinical trial - SafeBoosC. In addition different commercial NIRS oximeters were compared on changing haemoglobin oxygen saturation and compared against co-oximetry. The best calibration was achieved with a simple offset and a linear scaling of the OxyPrem rStO2 values. The INVOS adult and pediatric sensor gave systematically different values, while the difference between the NIRO® 300 and the two INVOS sensors were magnitude dependent. The co-oximetry proved unreliable on such low haemoglobin and high Intralipid levels.

The effects of closed tracheal suctioning plus volume guarantee on cerebral hemodynamics

OBJECTIVE

To compare the effects of open tracheal suctioning (OS) plus intermittent mandatory ventilation (IMV) vs. closed tracheal suctioning (CS) plus volume guarantee ventilation (VG) on changes in mean cerebral blood-flow velocity (CBFv) of ventilated very low birth weight (VLBW) infants.

STUDY DESIGN

A total of 75 normotensive, ventilated VLBW infants (with normal cranial ultrasounds) had monitoring of mean CBFv, PCO2 and mean arterial blood pressure (MABP) before, during and after 220 tracheal suctioning sessions during the first week of life. Multiple linear regression analysis was used to determine the factor(s) influencing the magnitude of relative changes from baseline in mean CBFv after suctioning.

RESULT

In all, 49 VLBW infants receiving IMV had monitoring during 124 OS sessions between July 2002 and May 2005; 26 VLBW infants receiving VG had monitoring during 96 CS sessions between January 2006 and July 2007. The average magnitude of relative changes in mean CBFv was significantly less with CS+VG, and was associated with the magnitude of relative changes in PCO2 and suctioning-ventilator group.

CONCLUSION

The average magnitude of relative changes in mean CBFv was reduced in VLBW infants with CS+VG vs. OS+IMV.

Early postnatal hypotension and developmental delay at 24 months of age among extremely low gestational age newborns

OBJECTIVES

To evaluate in extremely low gestational age newborns, relationships between indicators of hypotension during the first 24 postnatal hours and developmental delay at 24 months of age.

METHODS

The 945 infants in this prospective study were born at <28 weeks, were assessed for three indicators of hypotension in the first 24 postnatal hours, and were evaluated with the Bayley Mental Development Index (MDI) and Psychomotor Development Index (PDI) at 24 months corrected age. Indicators of hypotension included: (1) mean arterial pressure in the lowest quartile for gestational age; (2) treatment with a vasopressor; and (3) blood pressure lability, defined as the upper quartile for the difference between the lowest and highest mean arterial pressure. Logistic regression was used to evaluate relationships between hypotension and developmental outcomes, adjusting for potential confounders.

RESULTS

78% of infants in this cohort received volume expansion or vasopressor; all who received a vasopressor were treated with volume expansion. 26% had an MDI <70 and 32% had a PDI <70. Low MDI and PDI were associated with low gestational age, which in turn, was associated with receipt of vasopressor treatment. Blood pressure in the lowest quartile for gestational age was associated with vasopressor treatment and labile blood pressure. After adjusting for potential confounders, none of the indicators of hypotension were associated with MDI <70 or PDI <70.

CONCLUSIONS

In this large cohort of extremely low gestational age newborns, we found little evidence that early postnatal hypotension indicators are associated with developmental delay at 24 months corrected gestational age.

Near-infrared spectroscopy: a methodology-focused review

Near infrared spectroscopy (NIRS) is a light-based technology used to monitor tissue oxygen status. Refinements to the method since it was first described have extended its applicability to different research and clinical settings due to its non-invasiveness, instrument portability and ease of use. Classic NIRS recordings, based in the Beer-Lambert law, can be used for the trend monitoring of changes in tissue perfusion-oxygenation parting from an arbitrary zero point. However, in order to derive intermittently quantitative values in absolute terms, certain manoeuvres must be performed. More recently, the evolution of the technique has led to the development of instruments that provide an absolute value of regional hemoglobin saturation in a continuous manner. This review will focus on the physical principles of tissue spectroscopy including a brief description of the different operating principles that are currently in use or under development. The theoretical details, experimental procedures and data analysis involved in the measurements of physiological variables using NIRS will be described. The future beyond the scope of NIRS and potential lines of research will also be discussed.

Aplicação clínica da ultrassonografia craniana com Doppler em neonatos prematuros de muito baixo peso

OBJETIVO: Analisar o valor do diagnóstico precoce de alterações hemodinâmicas em hemorragias e eventos hipóxico-isquêmicos pela avaliação de imagens e mensuração do índice de resistência por meio da ultrassonografia craniana com Doppler em neonatos prematuros de muito baixo peso. MATERIAIS E MÉTODOS: Cinquenta neonatos prematuros de muito baixo peso foram submetidos a ultrassonografia craniana com Doppler com a técnica transfontanela anterior e transtemporal sequenciais. RESULTADOS: Foram detectadas alterações cerebrais em 32% dos prematuros, sendo 22% com hemorragia intracraniana, 8% com leucomalácia periventricular e 2% com toxoplasmose. Dentre os 34 casos (68%), do total de neonatos, nos quais não foram detectadas lesões cerebrais pela ultrassonografia craniana, 18 (53%) apresentaram alterações no índice de resistência. O índice de resistência variou conforme a época do exame. CONCLUSÃO: Existe correlação entre a presença de alterações na hemodinâmica cerebral e subsequente desenvolvimento de hemorragias e lesões hipóxico-isquêmicas, pela mensuração do índice de resistência. Alterações do índice de resistência, embora não preditoras de morte, estão relacionadas com a gravidade do quadro clínico em neonatos prematuros de muito baixo peso.

Effects of congenital heart disease on brain development

Brain and heart development occurs simultaneously in the fetus with congenital heart disease. Early morphogenetic programs in each organ share common genetic pathways. Brain development occurs across a more protracted time-course with striking brain growth and activity-dependent formation and refinement of connections in the third trimester. This development is associated with increased metabolic activity and the brain is dependent upon the heart for oxygen and nutrient delivery. Congenital heart disease leads to derangements of fetal blood flow that result in impaired brain growth and development that can be measured with advanced magnetic resonance imaging. Delayed development results in a unique vulnerability to cerebral white matter injury in newborns with congenital heart disease. Delayed brain development and acquired white matter injury may underlay mild but pervasive neurodevelopmental impairment commonly observed in children following neonatal congenital heart surgery.

Near-infrared spectroscopy measurements of cerebral oxygenation in newborns during immediate postnatal adaptation

OBJECTIVE

In view of growing concerns regarding the optimal supplementation of oxygen at birth, we measured cerebral oxygenation during the first minutes of life.

STUDY DESIGN

Using near-infrared spectroscopy, changes in cerebral oxygenated hemoglobin (O(2)Hb), dexoxygenated hemoglobin (HHb), and tissue oxygenation index (TOI) were measured during the first 15 minutes of life in 20 healthy newborn infants delivered at term by elective cesarean section.

RESULTS

O(2)Hb and TOI increased rapidly within the first minutes of life (median slope for O(2)Hb, 3.4 micromol/L/min; range, 1.4 to 20.6 micromol/L/min; median slope for TOI, 4.2 %/min; range, -0.4 to 27.3%/min), and cerebral HHb decreased (median slope, -4.8 micromol/L/min; range, -0.2 to -20.6 micromol/L/min). O(2)Hb, TOI, and HHb all reached a plateau within 8 minutes.

CONCLUSIONS

A significant increase in cerebral O(2)Hb and TOI and a significant decrease in HHb occur during immediate adaptation in healthy term newborns, reaching a steady plateau at around 8 minutes after birth.

Influence of ventilation mode on neonatal cerebral blood flow and volume

BACKGROUND

Cerebral hemodynamics is supposed to be influenced by the different ventilation approach. Ventilation support can be classified as non-invasive (N-CPAP) or invasive (SIMV and HFV), the last known to induce endotrauma. Our aim was the non-invasive NIRS assessment of neonatal absolute cerebral blood flow (CBF) and relative cerebral blood volume changes (DeltaCBV) during synchronized intermittent ventilation (SIMV), or high frequency ventilation (HFV) and nasal continuous positive airways pressure (CPAP).

METHODS

An observational study in a tertiary referral NICU. CBF and DeltaCBV changes were assessed in 41 preterm newborn infants with respiratory distress syndrome treated using mechanical ventilation or the CPAP device.

RESULTS

Basal chromophore traces enabled DeltaCBV (mL/100 g) changes to be calculated. CBF was calculated in mL/100 g/min from the saturation rise integral and rate of rise [O(2)Hb-HHb]. Median DeltaCBV was 0.07 (range 0.01-0.13) in SIMV group, 0.07 (0.01-0.19) in HFV group and 0.13 (0.10-1.28) in CPAP group. Median CBF was 14.44 (2.70-32.10), 9.20 (2.94-19.58) and 31.69 (13.59-34.93) respectively. A multiple regression model showed a significant correlation between DeltaCBV or CBF and ventilation approach.

CONCLUSION

In the light of our results, we might speculate that, assuming that hemodynamic autoregulation is safe and arterial blood pressure is preserved, ventilation per se influences brain circulation.

Cerebral blood flow velocities in extremely low birth weight infants with hypotension and infants with normal blood pressure

OBJECTIVE

To determine whether extremely low birth weight (ELBW) infants with hypotension have similar cerebral hemodynamics when compared with control subjects with normal blood pressure. We hypothesized that ELBW infants with low or normal blood pressure have similar cerebral blood flow (CBF) velocity.

STUDY DESIGN

In this case control study, CBF velocity (with Doppler ultrasound scanning), PCO2, and mean arterial blood pressure (MABP) were continuously monitored twice daily before intensive care procedures. If an infant became hypotensive (MABP < or = gestational age in weeks), additional monitoring was performed for 10 to 20 minutes, before treatment with dopamine. Thirty ELBW infants were enrolled (637 +/- 140 g, 24.2 +/- 1.1 weeks); 15 had hypotension, and 15 were gestational age/birth weight-matched control subjects with normal blood pressure. CBF velocity was compared by use of the Mann-Whitney U test.

RESULTS

The groups did not differ significantly in gestational age, birth weight, race, sex, PCO2, Apgar scores, or occurrence of severe intraventricular hemorrhage. There was no difference in mean CBF velocity (P = .934) in infants with hypotension (MABP: 23 [20-24.9] mm Hg) compared with infants with normal blood pressure (MABP: 32.6 [27.5-35.7] mm Hg).

CONCLUSION

Despite having hypotension, ELBW infants (before treatment) had similar CBF velocity compared with control subjects with normal blood pressure. On the basis of these results, hypotension may not indicate decreased CBF.

Background patterns and sleep-wake cycles on amplitude-integrated electroencephalography in preterms younger than 30 weeks gestational age with peri-/intraventricular haemorrhage

AIM

The objective of this prospective study was to evaluate the influence of peri-/intraventricular haemorrhage (PIVH) grades I-IV on amplitude-integrated electroencephalographic (aEEG) activity in preterm infants<30 weeks gestational age (GA).

METHODS

The aEEG tracings of the first 2 weeks of life of 56 preterm infants younger than 30 weeks GA (2 groups: group A=23-26 weeks GA, group B=27-29 weeks GA) born during a 4-year period with PIVH grades I-IV were assessed for the relative duration of four background aEEG activity patterns (continuous pattern, discontinuous high-voltage pattern, discontinuous low-voltage pattern and nearly isoelectric pattern), the presence of seizure activity and the appearance of sleep-wake cycles and compared to the tracings of 75 neurologically healthy preterms without PIVH.

RESULTS

Analysis of aEEG background activity showed a decrease of continuous activity whereas discontinuous activity increased in both groups with larger haemorrhages (grades III and IV) and when compared to controls. Suspected seizure activity was more common with increasing degree of bleeding in group A (50% with PIVH I or II, 75% with PIVH III or IV) and when compared to controls and was the same with increasing degree of bleeding in group B (47% with PIVH I or II, 45% with PIVH III or IV). Sleep-wake cycles were less common with larger haemorrhages in both groups (group A: 41% with PIVH I or II, 25% with PIVH III or IV; group B: 52% with PIVH I or II, 9% with PIVH III or IV) and when compared to controls.

CONCLUSIONS

The aEEG characteristics of severe PIVH consist in a combination of a more discontinuous background pattern, a lack of sleep-wake cycles and a higher likelihood of seizure activity when compared to age-matched controls.

A pilot study of changes in cerebral blood flow velocity, resistance, and vital signs following a painful stimulus in the premature infant

PURPOSE

The purpose of this pilot study was to determine the cerebral blood flow velocity and resistance changes and vital signs following a painful stimulus in the premature infant.

SUBJECTS

A convenience sample of 12 infants was randomly assigned to one of 2 treatment groups. In the final analysis, there were 10 infants younger than 24 hours of age and between 25 and 32 weeks' gestational age.

DESIGN

A randomized 2-period, 2-group, crossover design was used.

METHODS

Cerebral blood flow velocity and resistance were measured via a Doppler head ultrasound transducer placed over the anterior fontanel. Vital signs were measured with a cardiorespiratory monitor. The infant then received the heel stick procedure or the sham procedure (heel preparation with no heel puncture). Each infant served as his or her own control. After each procedure, there was ultrasound and vital sign measurement at 15, 60, 120, 180, 240, and 300 seconds. Thereafter, the alternate treatment was used and 6 more measurements were taken.

MAIN OUTCOME MEASURES

Cerebral values: peak systolic velocity (PSV) and resistive index (RI); vital signs: heart rate, respiratory rate, oxygen saturation (SpO2), and blood pressure.

RESULTS

Treatment groups were similar at baseline except for gestational age. There were no carryover or period effects in the crossover design for the primary outcomes except for SpO2. There was a significant group effect (heel stick compared with sham) (P = .009) for peak systolic velocity; however, there were no significant differences between groups at each time point. Two subjects had a distinctive pattern based on simultaneous changes in flow and resistance: when flow velocity increased, resistance decreased. This may be reflective of risk for intraventricular hemorrhage (IVH). Mean arterial blood pressure (MAP) was not significant. However, heart rate was significantly different between stick and sham at 15 seconds (P = .022); respiratory rate was significant at 180 seconds (P = .029); and SpO2 was significant at 3 different time points. There were no significant correlations between PSV and mean arterial blood pressure and PSV and SpO2 when comparing stick to sham.

CONCLUSIONS

This is a study based on a small sample size. However, the Doppler-measured peak systolic velocity increases significantly after a painful stimulus. The clinical implication of this finding needs to be established.

Does helmet CPAP reduce cerebral blood flow and volume by comparison with Infant Flow driver CPAP in preterm neonates?

OBJECTIVE

We compared neonatal helmet continuous positive airway pressure (CPAP) and the conventional nasal Infant Flow driver (IFD) CPAP in the noninvasive assessment of absolute cerebral blood flow (CBF) and relative cerebral blood volume changes (DeltaCBV) by near-infrared spectroscopy.

DESIGN AND SETTING

A randomized crossover study in a tertiary referral NICU.

PATIENTS AND INTERVENTIONS

Assessment of CBF and DeltaCBV in 17 very low birth weight infants with respiratory distress (median age 5 days) treated with two CPAP devices at a continuous distending pressure of 4 mbar.

MEASUREMENTS AND RESULTS

Neonates were studied for two consecutive 60-min periods with helmet CPAP and with IFD CPAP. Basal chromophore traces enabled DeltaCBV changes to be calculated. CBF was calculated in milliliters per 100 grams per minute from the saturation rise integral and rate of rise O(2)Hb-HHb. Median (range) CBF with helmet CPAP was 27.37 (9.47-48.20) vs. IFD CBF 34.74 (13.59-60.10)(p=0.049) and DeltaCBV 0.15 (0.09-0.28) with IFD and 0.13 (0.07-0.27) with helmet CPAP (NS). Using helmet and IFD CPAP, the neonates showed no difference in mean physiological parameters (transcutaneous carbon dioxide and oxygen tension, pulse oximetry saturation, heart rate, breathing rate, mean arterial blood pressure, desaturation rate, axillary temperature).

CONCLUSION

Assessing CBF and DeltaCBV measured by near-infrared spectroscopy with two CPAP devices revealed no differences in relative blood volume, but CBF was lower with helmet CPAP. Greater active vasoconstriction and/or passive capillary and/or venous vessel compression seem the most likely reason, due to a positive pressure around the head, neck, and shoulders by comparison with the airway pressure.

Development of cerebral blood flow volume in preterm neonates during the first two weeks of life

To investigate the postnatal development of cerebral perfusion in preterm neonates with normal brains over the first 2 wk of life, a prospective longitudinal study was designed. Quantitative measurement of cerebral blood flow (CBF) volume was performed using ultrasound flowmetry of the extracranial, brain-feeding arteries in 32 preterm infants of 28-35 wk gestational age. Measurements were done in the internal carotid and vertebral arteries of both sides on d 1, 2, 3, 7, and 14 after birth. A 10.0-MHz linear transducer of a computed sonography system (Acuson 128/XP10) was used. Intravascular flow volumes were calculated as the product of angle-corrected time-averaged flow velocity and the cross-sectional area of the vessel. Mean CBF volume increased markedly over the first 2 wk. One-third of this rise already occurred from the first to the second postnatal day, thereafter there was a continuous increase from d 2 to d 14 of life. Whereas the absolute level of CBF volume was primarily determined by postmenstrual age, the pattern of postnatal changes in CBF volume was found to be independent of gestational age. Arterial carbon dioxide tension, mean arterial blood pressure, and hematocrit had no influence on the development of CBF volume. The pronounced increase of CBF volume from d 1 to d 2 is likely to represent a normal adaptive response of the cerebral circulation to postnatal life. The data presented here may serve as the basis for further studies to investigate whether deviations from this adaptive response are associated with an increased risk of brain injury.

Cardiovascular support for low birth weight infants and cerebral hemodynamics: a randomized, blinded, clinical trial

BACKGROUND

Maintaining adequate organ blood flow is the target of vasopressor treatment, but the impact of these measures on cerebral perfusion has not yet been evaluated systematically in a randomized, blinded, clinical trial.

OBJECTIVES

To explore the effects on brain hemodynamics of 2 different inotropic agents used to treat systemic hypotension among low birth weight (LBW) infants.

DESIGN AND METHODS

Newborns of <1501 g birth weight or <32 weeks' gestational age, with a mean blood pressure (MBP) lower than gestational age in the first 24 hours of life, were assigned randomly to receive dopamine (DP) (2.5, 5, 7.5, or 10 microg/kg per minute; n = 28) or epinephrine (EP) (0.125, 0.250, 0.375, or 0.5 microg/kg per minute; n = 32), at doses that were increased in a stepwise manner every 20 minutes until the optimal MBP (MBP-OP) was attained and maintained.

OUTCOME MEASURES

Continuous monitoring of quantitative changes in cerebral concentrations of oxyhemoglobin and deoxyhemoglobin, cerebral intravascular oxygenation (HbD) (the difference between oxyhemoglobin and deoxyhemoglobin), and cerebral blood volume (CBV) were assessed with near-infrared spectroscopy. MBP, heart rate, transcutaneous Pco2 and Po2, and peripheral oxygen saturation were recorded continuously and analyzed at baseline, 20 minutes after each dose increase (T1, T2, T3, and T4) until MBP-OP was reached, and then every 20 minutes up to 1 hour of stable MBP-OP.

RESULTS

Fifty-nine infants were considered for analysis. Patients did not differ in birth weight or gestational age (1008 +/- 286 g and 28.3 +/- 2.3 weeks, respectively, in the DP group and 944 +/- 281 g and 27.7 +/- 2.4 weeks in the EP group). Studies were performed at a mean age of 5.3 +/- 3.7 hours of life (range: 2-16 hours). MBP-OP was attained for 96.3% of patients with DP and 93.7% with EP (responders). For those patients, MBP, heart rate, CBV, and HbD increased from baseline throughout the study period, with no differences between groups except for a higher heart rate with EP. Changes in MBP were correlated significantly with changes in HbD. Dose escalation of drugs produced no differences between groups in the behavior of the variables, except for a greater heart rate with EP from 20 minutes after dose 2 (T2) onward. Drug-induced changes in cerebral hemodynamics varied with gestational age; the EP-induced increase in CBV was greater among less mature patients (<28 weeks), whereas the DP-induced increase in CBV was greater among patients of > or =28 weeks.

CONCLUSIONS

Among hypotensive LBW infants, cardiovascular support with low/moderate-dose DP or low-dose EP increased cerebral perfusion, as indicated by the increase in both CBV and HbD. Low-dose EP was as effective as low/moderate-dose DP in increasing MBP among LBW infants.

Age-dependent cerebral hemodynamic effects of indomethacin in the newborn piglet

With recent discussions in the literature regarding prophylactic use of early (within the first 12 h after birth), low-dose indomethacin to reduce the incidence and severity of intraventricular hemorrhage, knowledge pertaining to the cerebral hemodynamic effects of indomethacin in this age group is of significant interest. The cerebral circulation is known to undergo significant changes during the first few days of postnatal life. In the present study, we have investigated the hypothesis that postnatal adaptive changes influence the cerebral hemodynamic response to indomethacin in an age-dependent manner. Near-infrared spectroscopy with indocyanine green was used to measure cerebral hemodynamics, cerebral metabolic rate of oxygen, and cerebral oxygen extraction fraction in 39 newborn piglets. Piglets were grouped by age and received either 0.2 mg/kg indomethacin (14 were <13 h of age and 12 were >13 h of age) or saline (8 were <13 h of age and 5 were >13 h of age) infusions. In a subgroup of indomethacin-treated piglets (9 less than and 7 greater than 13 h of age), Doppler flow ultrasound was used to diagnose and monitor the presence and persistence of patent ductus arteriosus. Age was a significant factor in the cerebral hemodynamic response to indomethacin with piglets <13 h of age exhibiting delayed increases in cerebral blood flow and cerebral blood volume at 150 min post-indomethacin infusion.

Low cerebral blood flow resistance in nonventilated preterm infants predicts poor neurologic outcome

OBJECTIVES

To examine whether cerebral blood flow variables during the first critical day of life can predict the 1-yr neurologic outcome in ventilated and nonventilated preterm infants.

DESIGN

Prospective follow-up study.

SETTING

Neonatal intensive care unit of university central hospital.

PATIENTS

Forty-nine preterm infants <33 wks of gestation.

INTERVENTIONS

Doppler ultrasound investigations of the brain circulation, heart rate, and systemic blood pressure were performed in ventilated (n = 35) and nonventilated (n = 14) preterm infants during the first day of life. The neurologic development was evaluated using Griffith's subscales at 12 months of corrected age.

MEASUREMENTS AND MAIN RESULTS

Cerebral blood flow velocity measurements were obtained from the anterior cerebral artery and internal carotid artery. Cerebral blood flow, cerebral blood flow resistance, and cerebral perfusion pressure subsequently were derived. These derived cerebral perfusion variables were associated with the sum of Griffith's developmental scales (p <.02). However, the slopes of regression lines between cerebral blood flow or cerebral blood flow resistance and the sum of Griffith's psychomotor developmental scales tended to be different in the ventilated and nonventilated infants (p =.06, p =.003, respectively). The correlations between these variables and the sum of Griffith's psychomotor developmental scales were significant only in nonventilated preterm infants (r =.69, p =.007, and r = -.85, p =.001, respectively).

CONCLUSIONS

Our data suggest that lowered cerebral blood flow resistance reflecting lowered cerebral blood flow during early circulatory transition is associated with adverse outcome in nonventilated preterm infants, but no connection in ventilated infants was found.

Evaluation of change of cerebral circulation by SpO2 in preterm infants with apneic episodes using near infrared spectroscopy

BACKGROUND

In the neonatal intensive care unit (NICU), hemodynamics in very low-birthweight infants are generally examined for oxygen saturation (SpO2), heart rate, respiration rate, and blood pressure. The present study examined how changes in cerebral circulation in preterm infants can be evaluated by the SpO2 monitoring method with near infrared spectroscopy (NIRS) to detect the cerebral circulation.

METHODS

The study was conducted in 11 low-birthweight neonates with a mean weight of 1252 g (940-1948 g), mean post-conceptional age of 28.9 weeks (28-31 weeks) and in whom a total of 145 apneic episodes were examined. Changes in cerebral circulation at the apneic attack were evaluated by two parameters of Delta HbD ( micro mol/L) for reduction in cerebral oxygenation and Delta cHb (mL/100 g brain) for variation in cerebral blood volume using the near infrared spectroscopy (NIRS).

RESULTS

There was a tendency for a reduction in cerebral oxygenation and a change in cerebral blood volume as SpO2 was reduced. In the event of apneic attacks where SpO2 was reduced to <85%, cerebral oxygen saturation was extensively reduced. In addition, cerebral blood volume was also greatly changed when the SpO2 was reduced to <85%, and changed further still when SpO2 was reduced again to < or =75%.

CONCLUSION

Reduction in SpO2 (<85%) was suggested to be an effective indication to changes in cerebral circulation. In the case of apneic attacks where SpO2 was < or =85%, the cerebral circulation in preterm low-birthweight neonates was extensively changed and, therefore, attention should be paid to changes in the concentration of SpO2 when managing apnea of prematurity in NICU.

Which to measure, systemic or organ blood flow? Middle cerebral artery and superior vena cava flow in very preterm infants

AIM

To describe, in very preterm babies, postnatal changes in measures of middle cerebral artery (MCA) Doppler variables. To relate these peripheral measures to echocardiographic measures of systemic blood flow and ductal shunting, and to study their relation to subsequent intraventricular haemorrhage (IVH).

METHODS

126 babies born before 30 weeks were studied with serial echocardiography and cerebral and Doppler ultrasound of the MCA at 5, 12, 24, and 48 hours of age. Echocardiographic measures included superior vena cava (SVC) flow and colour Doppler diameter of the ductal shunt. MCA Doppler measures included mean velocity, pulsatility index (PI), and estimated colour Doppler diameter.

RESULTS

MCA mean velocity increased whereas the PI decreased significantly over the first 48 hours. Babies with low SVC flow had significantly lower MCA mean velocity and estimated diameter than babies with normal SVC flow. There was no difference in PI. On multivariant analysis, the significant associations with MCA mean velocity were mean blood pressure (MBP), heart rate, SVC flow, and lower calculated vascular resistance. The significant associations with PI were larger ductal diameter and lower mean MBP. The significant associations with MCA diameter were higher SVC flow and lower calculated vascular resistance. After controlling for gestation, there was a highly significant association between lowest SVC flow and subsequent IVH but no association between IVH and lowest MCA mean velocity, estimated diameter, PI, or MBP.

CONCLUSIONS

These data are consistent with the speculation that SVC flow is a reflection of cerebral blood flow. Low SVC flow is more strongly associated with subsequent IVH than cerebral artery Doppler measures or MBP.

Noninvasive continuous monitoring of the effects of head position on brain hemodynamics in ventilated infants

HYPOTHESIS

Laying supine with the head in midline position improves cerebral venous return by preventing functional occlusion of the vessels of the neck.

OBJECTIVES

To assess changes in cerebral blood volume (DeltaCBV) and cerebral blood flow (CBF) with the position of the head in ventilated patients using a noninvasive method. The influence of the type of ventilation and birth weight was evaluated.

METHODS

Thirteen conventionally ventilated and 8 high-frequency oscillatory ventilated infants, with mean gestational ages and birth weights of 31 +/- 5 weeks (24--38) and 1575 +/- 803 g (560--3000), respectively, were studied 5.8 +/- 7.8 days (1--33) after birth. DeltaCBV (mL/100 g) and CBF (mL/100 g/min) were measured by near-infrared spectroscopy with the head in supine midline position (DeltaCBVs, CBFs) and rotated 90 to one side (DeltaCBVlat, CBFlat). Heart rate, peripheral saturation, transcutaneous PCO(2), and blood pressure were monitored continuously. Ventilatory settings remained constant throughout the study period.

RESULTS

Mean DeltaCBVs was lower than mean DeltaCBVlat, although no changes in blood pressure, transcutaneous PCO(2), oxygenation, or heart rate occurred. This change in DeltaCBV was not associated with the type of ventilation or birth weight, but the differences tended to be greater (dDeltaCBV = DeltaCBVlat-DeltaCBVs) in the smallest infants (<1200 g). In contrast, CBF did not vary.

CONCLUSION

The supine midline position of the head favors cerebral venous drainage and helps to prevent elevation of CBV.

SPECULATION

This finding may be important in the first days of life, particularly in tiny preterm infants recovering from lung disease with improving lung compliance, in which functional obstruction of cerebral venous drainage should be avoided.