Cerebral autoregulation in the first day after preterm birth: no evidence of association with systemic inflammation

Cerebral autoregulation in pediatric and neonatal intensive care: A scoping review

Deranged cerebral autoregulation (CA) is associated with worse outcome in adult brain injury. Strategies for monitoring CA and maintaining the brain at its 'best CA status' have been implemented, however, this approach has not yet developed for the paediatric population. This scoping review aims to find up-to-date evidence on CA assessment in children and neonates with a view to identify patient categories in which CA has been measured so far, CA monitoring methods and its relationship with clinical outcome if any. A literature search was conducted for studies published within 31st December 2022 in 3 bibliographic databases. Out of 494 papers screened, this review includes 135 studies. Our literature search reveals evidence for CA measurement in the paediatric population across different diagnostic categories and age groups. The techniques adopted, indices and thresholds used to assess and define CA are heterogeneous. We discuss the relevance of available evidence for CA assessment in the paediatric population. However, due to small number of studies and heterogeneity of methods used, there is no conclusive evidence to support universal adoption of CA monitoring, technique, and methodology. This calls for further work to understand the clinical impact of CA monitoring in paediatric and neonatal intensive care.

Near-infrared spectroscopy monitoring of neonatal cerebrovascular reactivity: where are we now?

Cerebrovascular reactivity defines the ability of the cerebral vasculature to regulate its resistance in response to both local and systemic factors to ensure an adequate cerebral blood flow to meet the metabolic demands of the brain. The increasing adoption of near-infrared spectroscopy (NIRS) for non-invasive monitoring of cerebral oxygenation and perfusion allowed investigation of the mechanisms underlying cerebrovascular reactivity in the neonatal population, confirming important associations with pathological conditions including the development of brain injury and adverse neurodevelopmental outcomes. However, the current literature on neonatal cerebrovascular reactivity is mainly still based on small, observational studies and is characterised by methodological heterogeneity; this has hindered the routine application of NIRS-based monitoring of cerebrovascular reactivity to identify infants most at risk of brain injury. This review aims (1) to provide an updated review on neonatal cerebrovascular reactivity, assessed using NIRS; (2) to identify critical points that need to be addressed with targeted research; and (3) to propose feasibility trials in order to fill the current knowledge gaps and to possibly develop a preventive or curative approach for preterm brain injury. IMPACT: NIRS monitoring has been largely applied in neonatal research to assess cerebrovascular reactivity in response to blood pressure, PaCO2 and other biochemical or metabolic factors, providing novel insights into the pathophysiological mechanisms underlying cerebral blood flow regulation. Despite these insights, the current literature shows important pitfalls that would benefit to be addressed in a series of targeted trials, proposed in the present review, in order to translate the assessment of cerebrovascular reactivity into routine monitoring in neonatal clinical practice.

Insights into Neonatal Cerebral Autoregulation by Blood Pressure Monitoring and Cerebral Tissue Oxygenation: A Qualitative Systematic Review

OBJECTIVE

The aim of this qualitative systematic review was to identify publications on blood pressure monitoring in combination with cerebral tissue oxygenation monitoring during the first week after birth focusing on cerebral autoregulation.

METHODS

A systematic search was performed on PubMed. The following search terms were used: infants/newborn/neonates, blood pressure/systolic/diastolic/mean/MAP/SAP/DAP, near-infrared spectroscopy, oxygenation/saturation/oxygen, and brain/cerebral. Additional studies were identified by a manual search of references in the retrieved studies and reviews. Only human studies were included.

RESULTS

Thirty-one studies focused on preterm neonates, while five included preterm and term neonates. In stable term neonates, intact cerebral autoregulation was shown by combining cerebral tissue oxygenation and blood pressure during immediate transition, while impaired autoregulation was observed in preterm neonates with respiratory support. Within the first 24 h, stable preterm neonates had reduced cerebral tissue oxygenation with intact cerebral autoregulation, while sick neonates showed a higher prevalence of impaired autoregulation. Further cardio-circulatory treatment had a limited effect on cerebral autoregulation. Impaired autoregulation, with dependency on blood pressure and cerebral tissue oxygenation, increased the risk of intraventricular hemorrhage and abnormal neurodevelopmental outcomes.

CONCLUSIONS

Integrating blood pressure monitoring with cerebral tissue oxygenation measurements has the potential to improve treatment decisions and optimizes neurodevelopmental outcomes in high-risk neonates.

Delayed cord clamping: Time for physiologic implementation

Delayed cord clamping has been shown to be beneficial in both preterm and term babies. Practice guidelines have not been consistent between centers and the practice of delayed cord clamping has not been standardized. The concept of physiologic-based cord clamping emerged into practice as well. Cord milking has different physiological effect and might be harmful in preterm babies.

Cerebral oxygenation monitoring of ex-preterm infants during the infant car seat challenge test

The American Academy of Pediatrics and until recently the Canadian Paediatric Society recommend preterm infants undergo an Infant Car Seat Challenge test prior to discharge to rule out systemic oxygen desaturation when placed at a 45-degree angle in a car seat. Near-infrared spectroscopy (NIRS) provides objective measurements of the impact of systemic oxygen (SO₂) desaturation, bradycardia, or both on cerebral regional oxygen saturation (rSO₂).

Objective

To characterize baseline cerebral rSO₂ during a car seat trial in preterm infants ready for discharge.

Design/Methods

A prospective observational study was performed in 20 infants (32 ± 5 weeks [mean] at a postmenstrual age 37 ± 6 weeks [mean]). Cerebral rSO₂ was continuously monitored by placing a NIRS transducer on head during Infant Car Seat Challenge (ICSC). Failure of an ICSC was defined as two SO₂ desaturation events below 85% for more than 20 seconds or one event below 80% for 10 seconds.

Results

The lowest SO₂ was 70% with a lowest NIRS recording of 68%. Three infants failed their ICSC, with the lowest rSO₂ in these three infants being 68%, above the lowest acceptable limit of 55%. Heart rate but not SO₂ appears to influence rSO₂ over the range of cerebral oxygenation seen.

Conclusions

Baseline cerebral rSO₂ during ICSC oscillates between 68 and 90%. There were no episodes of significant cerebral oxygen desaturation in studied infants regardless of whether they passed or failed the ICSC. We postulate that former preterm infants are capable through cerebral autoregulation, of maintaining adequate cerebral blood flow in the presence of either systemic oxygen desaturation or bradycardia when they are otherwise ready for discharge.

Cerebral Autoregulation in Sick Infants: Current Insights

Cerebrovascular autoregulation is the ability to maintain stable cerebral blood flow within a range of cerebral perfusion pressures. When cerebral perfusion pressure is outside the limits of effective autoregulation, the brain is subjected to hypoperfusion or hyperperfusion, which may cause vascular injury, hemorrhage, and/or hypoxic white matter injury. Infants born preterm, after fetal growth restriction, with congenital heart disease, or with hypoxic-ischemic encephalopathy are susceptible to a failure of cerebral autoregulation. Bedside assessment of cerebrovascular autoregulation would offer the opportunity to prevent brain injury. Clinicians need to know which patient populations and circumstances are associated with impaired/absent cerebral autoregulation.

Cerebrovascular autoregulation in preterm fetal growth restricted neonates

OBJECTIVE

To investigate the effect of fetal growth restriction (FGR) on cerebrovascular autoregulation in preterm neonates during the first 3 days of life.

DESIGN

Case-control study.

SETTING

Neonatal intensive care unit of the Wilhelmina Children's Hospital, The Netherlands.

PATIENTS

57 FGR (birth weight <10th percentile) and 57 appropriate for gestational age (AGA) (birth weight 20th-80th percentiles) preterm neonates, matched for gender, gestational age, respiratory and blood pressure support.

METHODS

The correlation between continuously measured mean arterial blood pressure and regional cerebral oxygen saturation was calculated to generate the cerebral oximetry index (COx). Mean COx was calculated for each patient for each postnatal day. The percentage of time with impaired autoregulation (COx>0.5) was also calculated.

RESULTS

FGR neonates had higher mean COx values than their AGA peers on day 2 (0.15 (95% CI 0.11 to 0.18) vs 0.09 (95% CI 0.06 to 0.13), p=0.029) and day 3 (0.17 (95% CI 0.13 to 0.20) vs 0.09 (95% CI 0.06 to 0.12), p=0.003) of life. FGR neonates spent more time with impaired autoregulation (COx value >0.5) than controls on postnatal day 2 (19% (95% CI 16% to 22%) vs 14% (95% CI 12% to 17%), p=0.035) and day 3 (20% (95% CI 17% to 24%) vs 15% (95% CI 12% to 18%), p=0.016).

CONCLUSION

FGR preterm neonates more frequently display impaired cerebrovascular autoregulation compared with AGA peers on days 2 and 3 of life which may predispose them to brain injury. Further studies are required to investigate whether this impairment persists beyond the first few days of life and whether this impairment is linked to poor neurodevelopmental outcome.

An Integrative Review of Cytokine/Chemokine Predictors of Neurodevelopment in Preterm Infants

Preterm infants are at risk of brain injury and poor neurodevelopmental outcomes including impairments in cognition, behavioral functioning, sensory perception, and motor performance. Systemic inflammation has been identified as an important, potentially modifiable precursor of neurologic and neurodevelopmental impairments. Inflammation is typically measured by quantifying circulating cytokines and chemokines. However, it is unclear which specific cytokines/chemokines most consistently predict neurodevelopment in preterm infants. In this integrative review, we evaluated and analyzed the literature (N = 37 publications) to determine the cytokines/chemokines most predictive of neurodevelopment in preterm infants, the optimal timing for these measurements, and the ideal source for collecting cytokines/chemokines. Synthesis of the findings of these studies revealed that interleukin (IL)-6, IL-1β, IL-8, and tumor necrosis factor (TNF)-α collected during the first 3 weeks of life are most predictive of subsequent neurodevelopment. Methodological variation among studies hinders more specific analysis, including the evaluation of cytokine thresholds and meta-analyses, that would allow for the use of cytokines/chemokines to predict neurodevelopment. Future research should focus on identifying explicit cytokine values, specifically for IL-6, IL-1β, IL-8, and TNF-α, that are most predictive for identifying preterm infants most at risk of impairment, keeping in mind that longitudinal measures of cytokines/chemokines may be more predictive of future outcomes than single-time point measures.

Measuring Near-Infrared Spectroscopy Derived Cerebral Autoregulation in Neonates: From Research Tool Toward Bedside Multimodal Monitoring

Introduction: Cerebral autoregulation (CAR), the ability of the human body to maintain cerebral blood flow (CBF) in a wide range of perfusion pressures, can be calculated by describing the relation between arterial blood pressure (ABP) and cerebral oxygen saturation measured by near-infrared spectroscopy (NIRS). In literature, disturbed CAR is described in different patient groups, using multiple measurement techniques and mathematical models. Furthermore, it is unclear to what extent cerebral pathology and outcome can be explained by impaired CAR. Aim and methods: In order to summarize CAR studies using NIRS in neonates, a systematic review was performed in the PUBMED and EMBASE database. To provide a general overview of the clinical framework used to study CAR, the different preprocessing methods and mathematical models are described and explained. Furthermore, patient characteristics, definition of impaired CAR and the outcome according to this definition is described organized for the different patient groups. Results: Forty-six articles were included in this review. Four patient groups were established: preterm infants during the transitional period, neonates receiving specific medication/treatment, neonates with congenital heart disease and neonates with hypoxic-ischemic encephalopathy (HIE) treated with therapeutic hypothermia. Correlation, coherence and transfer function (TF) gain are the mathematical models most frequently used to describe CAR. The definition of impaired CAR is depending on the mathematical model used. The incidence of intraventricular hemorrhage in preterm infants is the outcome variable most frequently correlated with impaired CAR. Hypotension, disease severity, dopamine treatment, injury on magnetic resonance imaging (MRI) and long term outcome are associated with impaired CAR. Prospective interventional studies are lacking in all research areas. Discussion and conclusion: NIRS derived CAR measurement is an important research tool to improve knowledge about central hemodynamic fluctuations during the transitional period, cerebral pharmacodynamics of frequently used medication (sedatives-inotropes) and cerebral effects of specific therapies in neonatology. Uniformity regarding measurement techniques and mathematical models is needed. Multimodal monitoring databases of neonatal intensive care patients of multiple centers, together with identical outcome parameters are needed to compare different techniques and make progress in this field. Real-time bedside monitoring of CAR, together with conventional monitoring, seems a promising technique to improve individual patient care.

Early biomarkers of brain injury and cerebral hypo- and hyperoxia in the SafeBoosC II trial

BACKGROUND

The randomized clinical trial, SafeBoosC II, examined the effect of monitoring of cerebral oxygenation by near-infrared spectroscopy combined with a guideline on treatment when cerebral oxygenation was out of the target range. Data on cerebral oxygenation was collected in both the intervention and the control group. The primary outcome was the reduction in the burden of cerebral hypo- and hyperoxia between the two groups. In this study we describe the associations between the burden of cerebral hypo- and hyperoxia, regardless of allocation to intervention or control group, and the biomarkers of brain injury from birth till term equivalent age that was collected as secondary and explorative outcomes in the SafeBoosC II trial.

METHODS

Cerebral oxygenation was continuously monitored during the first 72h of life in 166 extremely preterm infants. Cranial ultrasound was performed at day 1,4,7,14, and 35 and at term. Electroencephalogram (EEG) was recorded at 64h. Blood-samples taken at 6 and 64 hours were analysed for the brain injury biomarkers; S100beta, brain-fatty-acid-binding-protein, and neuroketal. All analyses were conducted post hoc.

RESULTS

Significantly more infants with a cerebral burden of hypoxia within the 4th quartile versus infants within quartile 1-3 were diagnosed with severe intracranial haemorrhage (11/39 versus 11/117, p = 0.003), had low burst rate on EEG (12/28 versus 21/103, p = 0.015), or died (14/41 versus 18/123, p = 0.006), whereas none of these events were significantly associated with cerebral hyperoxia. The blood biomarkers were not significantly associated with the burden of cerebral hypo- or hyperoxia.

CONCLUSIONS

The explorative analysis showed that early burden of cerebral hypoxia, but not hyperoxia was significantly associated with low brain electrical activity and severe intracranial haemorrhage while none of the three blood biomarkers were associated with the burden of either cerebral hypo- or hyperoxia.

Intrauterine inflammation, cerebral oxygen consumption and susceptibility to early brain injury in very preterm newborns

BACKGROUND

In utero exposure to inflammation results in elevated cerebral oxygen consumption. This increased metabolic demand may contribute to the association between chorioamnionitis and intraventricular haemorrhage (P/IVH). We hypothesised that intrauterine inflammation imposes an elevated cerebral metabolic load and increased fractional oxygen extraction (cFTOE) with cFTOE further increased in the presence of early P/IVH.

METHODS

Eighty-three infants ≤30 weeks gestation were recruited. Exposure to intrauterine inflammation was determined by placental histology. Total internal carotid blood flow (Doppler ultrasound) and near infrared spectroscopy were measured and cerebral oxygen delivery (mcerbDO2), consumption (mcerbVO2) and cFTOE were calculated on days 1 and 3 of life. Primary outcome was defined as death or P/IVH >grade II (cranial sonograph) by day 3.

RESULTS

Infants exposed to intrauterine inflammation had higher total internal carotid blood flow (92 vs 63 mL/kg/min) and mcerbDO2 (13.7 vs 10.1 mL/kg/min) than those not exposed to inflammation. Newborns with P/IVH had both higher oxygen consumption and extraction compared with those without sonographic injury regardless of exposure to intrauterine inflammation. Further, in preterms exposed to inflammation, those with P/IVH had higher consumption (6.1 vs 4.8 mL/kg/min) and extraction than those without injury. These differences were observed only on day 1 of life.

CONCLUSIONS

Although P/IVH is multifactorial in preterm newborns, it is likely that cerebral hypoxic-ischaemia plays a central pathophysiological role. These data provide a mechanistic insight into this process and suggests that the increased cerebral metabolic load imposed by the presence of inflammation results in a higher risk of critical hypoxic ischaemia in the preterm with increased susceptibility to significant P/IVH.

Effects of ventilation modalities on near-infrared spectroscopy in surgically corrected CDH infants

BACKGROUND

Near-infrared spectroscopy (NIRS) is a noninvasive technique for monitoring tissue oxygenation and perfusion. The aim of this study was to evaluate cerebral and splanchnic NIRS changes in CDH operated infants enrolled into the VICI trial and therefore randomized for ventilatory modalities.

MATERIALS AND METHODS

CDH newborns enrolled into the VICI trial (Netherlands Trial Register, NTR 1310) were randomized at birth for high-frequency oscillatory ventilation (HFOV) or conventional mechanical ventilation (CMV) according to the trial. Cerebral oxygenation (rSO2C) and splanchnic oxygenation (rSO2S) were obtained by NIRS (INVOS 5100; Somanetics, Troy, MI) before and after surgery. Variations in rSO2C and rSO2S were evaluated. Mann-Whitney test and one-way ANOVA were used as appropriate. p<0.05 was considered significant.

RESULTS

Thirteen VICI trial patients underwent surgical repair between March 2011 and December 2012, and were enrolled in the study. Seven patients were assigned to HFOV and six to CMV group respectively. During surgery, a significant reduction in rSO2C (p=0.0001) and rSO2S (p=0.005) were observed. HFOV patients experienced prolonged reduction in rSO2C value (p=0.003) while rSO2S did not vary between HFOV and CMV (p=0.94).

CONCLUSIONS

Surgical CDH repair was associated with decrease of cerebral and splanchnic oxygenation, regardless of ventilation. Patients ventilated by HFOV need a longer time interval to recovery normal rSO2C values, than those ventilated by CMV. This may be owing to a different impact of HFOV on patients' hemodynamic status with a higher impairment on total venous return and its negative consequences on cardiac output.

Cerebral autoregulation in the preterm newborn using near-infrared spectroscopy: a comparison of time-domain and frequency-domain analyses

The aim was to compare two conventional methods used to describe cerebral autoregulation (CA): frequency-domain analysis and time-domain analysis. We measured cerebral oxygenation (as a surrogate for cerebral blood flow) and mean arterial blood pressure (MAP) in 60 preterm infants. In the frequency domain, outcome variables were coherence and gain, whereas the cerebral oximetry index (COx) and the regression coefficient were the outcome variables in the time domain. Correlation between coherence and COx was poor. The disagreement between the two methods was due to the MAP and cerebral oxygenation signals being in counterphase in three cases. High gain and high coherence may arise spuriously when cerebral oxygenation decreases as MAP increases; hence, time-domain analysis appears to be a more robust—and simpler—method to describe CA.

Dopamine therapy is associated with impaired cerebral autoregulation in preterm infants

AIM

Hypotension is a common problem in newborn infants and is associated with increased mortality and morbidity. Dopamine is the most commonly used antihypotensive drug therapy, but has never been shown to improve neurological outcomes. This study tested our hypothesis that dopamine affects cerebral autoregulation (CA).

METHODS

Near-infrared spectroscopy was used to measure the cerebral oxygenation index in 60 very preterm infants, and mean arterial blood pressure was monitored towards the end of their first day of life. Measurements were performed continuously for two to three hour periods. CA was quantified as the cerebral oximetry index (COx).

RESULTS

We treated 13 of the 60 infants (22%) with dopamine during the measurements. COx was higher in the dopamine group than the untreated group (0.41 ± 0.25 vs. 0.08 ± 0.25, p < 0.001). Blood pressure tended to be lower in the dopamine group, but the anticipated difference in cerebral oxygenation was not detected. The need for mechanical ventilation in the first day of life and incidences of mortality was higher in the dopamine group.

CONCLUSION

Dopamine therapy was associated with decreased CA in preterm infants. We were unable to determine whether dopamine directly impaired CA or was merely an indicator of illness.

New time-frequency method for cerebral autoregulation in newborns: predictive capacity for clinical outcomes

OBJECTIVE

To describe an alternative analysis in the frequency-domain of the temporal relationship between 2 biological signals and evaluate the method's predictive capacity for classifying infants at risk for an adverse outcome.

STUDY DESIGN

We studied 54 infants (mean gestational age 27 weeks) with invasive mean arterial blood pressure monitoring. The bivariate autoregressive spectral coherence (BiAR-COH) method and the spectral coherence methods were used to analyze the relationship between spontaneous changes in mean arterial blood pressure and the near-infrared tissue oxygenation index.

RESULTS

The mean postnatal age at the beginning and end of the autoregulation study was 6.0 (3.0) and 29.0 (7.5) hours, respectively. The BiAR-COH was superior to the spectral coherence in predicting low superior vena cava (SVC) flow (≤ 41 mL/kg per minute), with an area under the receiver operating characteristic curve of 0.84 (95% CI, 0.77-0.90; P < .001). The BiAR-COH threshold for identifying low SVC flow was 0.577, with 0.8 sensitivity and 0.76 specificity. After adjusting for the repeated measures effect (multiple epochs) in a given patient, the averaged BiAR-COH per patient and averaged COH per patient were calculated as the average value per patient. The pBiAR-COH (but not the pCOH) was associated with intraventricular hemorrhage grades 3 and 4 and predicted mortality.

CONCLUSIONS

The BiAR-COH classifier identifies low SVC flow infants who are at risk for brain hypoperfusion. The BiAR-COH is superior to frequency domain methods in predicting adverse outcomes in infants.

Cerebral oxygenation in preterm infants

BACKGROUND AND OBJECTIVE

Prone sleeping is a major risk factor for sudden infant death syndrome (SIDS) and preterm infants are at significantly increased risk. In term infants, prone sleeping is associated with reduced mean arterial pressure (MAP) and cerebral tissue oxygenation index (TOI). However, little is known about the effects of sleeping position on TOI and MAP in preterm infants. We aimed to examine TOI and MAP in preterm infants after term-equivalent age, during the period of greatest SIDS risk.

METHODS

Thirty-five preterm and 17 term infants underwent daytime polysomnography, including measurement of TOI (NIRO-200 spectrophotometer, Hamamatsu Photonics KK, Japan) and MAP (Finapress Medical Systems, Amsterdam, Netherlands) at 2 to 4 weeks, 2 to 3 months, and 5 to 6 months postterm age. Infants slept prone and supine in active and quiet sleep. The effects of sleep state and position were determined by using 2-way repeated measures analysis of variance and of preterm birth by using 2-way analysis of variance.

RESULTS

In preterm infants, TOI was significantly lower when prone compared with supine in both sleep states at all ages (P < .05). Notably, TOI was significantly lower in preterm compared with term infants at 2 to 4 weeks, in both positions (P < .05), and at 2 to 3 months when prone (P < .001), in both sleep states. MAP was also lower in preterm infants in the prone position at 2 to 3 months (P < .01).

CONCLUSIONS

Cerebral oxygenation is reduced in the prone position in preterm infants and is lower compared with age-matched term infants, predominantly in the prone position when MAP is also reduced. This may contribute to their increased SIDS risk.

Skin microcirculation in healthy term newborn infants--assessment of morphology, perfusion and oxygenation

Despite microcirculation's fundamental role, assessments of its function are limited. We explored the applicability of Computer Assisted Video Microscope (CAVM), Laser Doppler Perfusion Measurements (LDPM) and Diffuse Reflectance Spectroscopy (DRS) to study skin microvascular morphology, perfusion and oxygen saturation in twenty-five healthy newborns day 1-3 of life.

RESULTS

Day 1-3 (mean (SD)): Microvascular density (CAVM; number of microvessels crossing a grid of lines/mm line, c/mm): Chest: 11.3 (1.5), 11.0 (1.7), 10.7 (1.6). Hand: 13.2 (2.0), 13.2 (1.9), 12.4 (1.6). Capillary density was significantly higher in the hand than in the chest each day (p <  0.001). Perfusion (LDPM; arbitrary units): Chest: 109.1 (26.0), 101.4 (24.6), 100.8 (25.3). Hand: 58.9 (17.5), 54.3 (15.8), 46.9 (14.8). Perfusion was significantly higher in the chest than in the hand each day (p <  0.01). Microvascular oxygen saturation (DRS; %): Chest: 88.1 (5.2), 87.8 (10.0), 86.7 (9.0). Hand: 79.9 (15.2), 82.7 (11.8), 82.2 (12.1) (p <  0.05). Capillary flow velocities (CAVM) were similar in the chest and hand: 60-70% capillaries had "continuous high flow" and 30-40% "continuous low flow".Multimodal skin microvascular assessments with CAVM, LDPM and DRS are feasible with reproducible data in newborns. The hand has lower perfusion, higher capillary density and higher oxygen extraction than the chest.

The development of cardiovascular and cerebral vascular control in preterm infants

Over the past three decades there has been a steady increase in the incidence of preterm birth. The worldwide rate of preterm birth is estimated to be 9.6% of all births, a total of almost 13 million births annually. Preterm birth is associated with a range of adverse cardiovascular and central nervous system outcomes, which may be attributed to altered development of these systems following preterm birth. Preterm birth has a considerable impact on cardiovascular parameters with preterm infants displaying higher heart rates and reduced blood pressure when compared to term born infants at matched ages. Furthermore, premature infants have altered autonomic control of cardiovascular parameters which manifests as abnormalities in heart rate variability and baroreflex mediated control of heart rate and blood pressure. As a result, systemic cardiovascular parameters can be unstable following preterm birth which may place stress on the neonatal brain. The brain of a preterm infant is particularly vulnerable to these fluctuations due to immature cerebral haemodynamics. Preterm infants, particularly those who are very preterm or unwell, display fluctuating pressure-passivity between systemic blood pressure and cerebral blood flow representing a considerably increased risk of cerebral haemorrhage or hypoxia. This is further compounded by immaturity of cerebral blood flow-metabolism coupling, which means increased metabolic demand cannot adequately be met by increased cerebral blood flow. It has been suggested that adverse long-term outcomes following preterm birth may occur as a result of exposure to physiological stress either in-utero or early in infancy.

Cerebral effects of commonly used vasopressor-inotropes: a study in newborn piglets

Background

Despite widespread use in sick infants, it is still debated whether vasopressor-inotropes have direct cerebral effects that might affect neurological outcome. We aimed to test direct cerebrovascular effects of three commonly used vasopressor-inotropes (adrenaline, dopamine and noradrenaline) by comparing the responses to those of nonpharmacologically induced increases in blood pressure. We also searched for reasons for a mismatch between the response in perfusion and oxygenation.

Methods

Twenty-four piglets had long and short infusions of the three vasopressor-inotropes titrated to raise mean arterial blood pressure (MAP) 10 mmHg in random order. Nonpharmacological increases in MAP were induced by inflation of a balloon in the descending aorta. We measured cerebral oxygenation (near-infrared spectroscopy), perfusion (laser-Doppler), oxygen consumption (co-oximetry of arterial and superior sagittal sinus blood), and microvascular heterogeneity (side stream dark field video microscopy).

Results

Vasopressor-inotropes increased cerebral oxygenation significantly less (p≤0.01) compared to non-pharmacological MAP increases, whereas perfusion was similar. Furthermore, cerebral total hemoglobin concentration increased significantly less during vasopressor-inotrope infusions (p = 0.001). These physiologic responses were identical between the three vasopressor-inotropes (p>0.05). Furthermore, they induced a mild, although insignificant increase in cerebral metabolism and microvascular heterogeneity (p>0.05). Removal of the scalp tissue did not influence the mismatch (p>0.05).

Conclusion

We demonstrated a moderate vasopressor-inotrope induced mismatch between cerebral perfusion and oxygenation. Scalp removal did not affect this mismatch, why vasopressor-inotropes appear to have direct cerebral actions. The statistically nonsignificant increases in cerebral metabolism and/or microvascular heterogeneity may explain the mismatch. Alternatively, it may simply reflect a vasopressor-inotrope-induced decrease in the arterial-to-venous volume ratio as detected by near-infrared spectroscopy.