Carbon Dioxide Fluctuations Are Associated with Changes in Cerebral Oxygenation and Electrical Activity in Infants Born Preterm

Cerebrovascular reactivity to carbon dioxide tension in newborns: data from combined time-resolved near-infrared spectroscopy and diffuse correlation spectroscopy

Significance

Critically ill newborns are at risk of brain damage from cerebrovascular disturbances. A cerebral hemodynamic monitoring system would have the potential role to guide targeted intervention.

Aim

To obtain, in a population of newborn infants, simultaneous near-infrared spectroscopy (NIRS)-based estimates of cerebral tissue oxygen saturation (StO 2 ) and blood flow during variations of carbon dioxide tension (pCO 2 ) levels within physiologic values up to moderate permissive hypercapnia, and to examine if the derived estimate of metabolic rate of oxygen would stay constant, during the same variations.

Approach

We enrolled clinically stable mechanically ventilated newborns at postnatal age > 24    h without brain abnormalities at ultrasound. StO 2 and blood flow index were measured using a non-invasive device (BabyLux), which combine time-resolved NIRS and diffuse-correlation spectroscopy. The effect of changes in transcutaneous pCO 2 on StO 2 , cerebral blood flow (CBF), and cerebral metabolic rate of oxygen index (tCMRO 2 i ) were estimated.

Results

Ten babies were enrolled and three were excluded. Median GA at enrollment was 39 weeks and median weight 2720 g. StO 2 increased 0.58% (95% CI 0.55; 0.61, p < 0.001 ), CBF 2% (1.9; 2.3, p < 0.001 ), and tCMRO 2 0.3% (0.05; 0.46, p = 0.017 ) per mmHg increase in pCO 2 .

Conclusions

BabyLux device detected pCO 2 -induced changes in cerebral StO 2 and CBF, as expected. The small statistically significant positive relationship between pCO 2 and tCMRO 2 i variation is not considered clinically relevant and we are inclined to consider it as an artifact.

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.

Newer indications for neuromonitoring in critically ill neonates

Continuous neuromonitoring in the neonatal intensive care unit allows for bedside assessment of brain oxygenation and perfusion as well as cerebral function and seizure identification. Near-infrared spectroscopy (NIRS) reflects the balance between oxygen delivery and consumption, and use of multisite monitoring of regional oxygenation provides organ-specific assessment of perfusion. With understanding of the underlying principles of NIRS as well as the physiologic factors which impact oxygenation and perfusion of the brain, kidneys and bowel, changes in neonatal physiology can be more easily recognized by bedside providers, allowing for appropriate, targeted interventions. Amplitude-integrated electroencephalography (aEEG) allows continuous bedside evaluation of cerebral background activity patterns indicative of the level of cerebral function as well as identification of seizure activity. Normal background patterns are reassuring while abnormal background patterns indicate abnormal brain function. Combining brain monitoring information together with continuous vital sign monitoring (blood pressure, pulse oximetry, heart rate and temperature) at the bedside may be described as multi-modality monitoring and facilitates understanding of physiology. We describe 10 cases in critically ill neonates that demonstrate how comprehensive multimodal monitoring provided greater recognition of the hemodynamic status and its impact on cerebral oxygenation and cerebral function thereby informing treatment decisions. We anticipate that there are numerous other uses of NIRS as well as NIRS in conjunction with aEEG which are yet to be reported.

Neuromonitoring in neonatal critical care part II: extremely premature infants and critically ill neonates

Neonatal intensive care has expanded from cardiorespiratory care to a holistic approach emphasizing brain health. To best understand and monitor brain function and physiology in the neonatal intensive care unit (NICU), the most commonly used tools are amplitude-integrated EEG, full multichannel continuous EEG, and near-infrared spectroscopy. Each of these modalities has unique characteristics and functions. While some of these tools have been the subject of expert consensus statements or guidelines, there is no overarching agreement on the optimal approach to neuromonitoring in the NICU. This work reviews current evidence to assist decision making for the best utilization of these neuromonitoring tools to promote neuroprotective care in extremely premature infants and in critically ill neonates. Neuromonitoring approaches in neonatal encephalopathy and neonates with possible seizures are discussed separately in the companion paper. IMPACT: For extremely premature infants, NIRS monitoring has a potential role in individualized brain-oriented care, and selective use of aEEG and cEEG can assist in seizure detection and prognostication. For critically ill neonates, NIRS can monitor cerebral perfusion, oxygen delivery, and extraction associated with disease processes as well as respiratory and hypodynamic management. Selective use of aEEG and cEEG is important in those with a high risk of seizures and brain injury. Continuous multimodal monitoring as well as monitoring of sleep, sleep-wake cycling, and autonomic nervous system have a promising role in neonatal neurocritical care.

Multimodal Assessment of Systemic Blood Flow in Infants

The assessment of systemic blood flow is a complex and comprehensive process with clinical, laboratory, and technological components. Despite recent advancements in technology, there is no perfect bedside tool to quantify systemic blood flow in infants that can be used for clinical decision making. Each option has its own merits and limitations, and evidence on the reliability of these physiology-based assessment processes is evolving. This article provides an extensive review of the interpretation and limitations of methods to assess systemic blood flow in infants, highlighting the importance of a comprehensive and multimodal approach in this population.

Pulse Oximetry Saturation (Spo2) Monitoring in the Neonatal Intensive Care Unit (NICU): The Challenge for Providers: A Systematic Review

BACKGROUND

In the neonatal intensive care unit (NICU), maintaining an oxygenation level that avoids both hypoxemia and hyperoxemia is challenging. Pulse oximetry has become fundamental for noninvasive monitoring of saturation of peripheral oxygen (Spo2) in preterm newborns.

PURPOSE

The aim of this systematic review is to determine Spo2 target values in order to avoid hypoxemia or hyperoxemia and complications arising from these.

METHOD AND SEARCH STRATEGY

For this systematic review, articles were audited from 2010 to 2020 using the PRISMA guidelines. PubMed, MEDLINE, Google Scholar, and Scopus databases were used, and search terms were related to use of pulse oximetry in the NICU.

RESULTS

The result showed that 12 of 20 (60%) studies focused on target values but without a unanimous agreement on values, although 5 of 12 studies (41.66%) suggested a lower value target of 85% and 4 of 12 studies (33.33%) recommended 95% as the higher target value. Other authors showed no difference in the incidence of adverse events comparing different target values and focused the importance more on the fluctuation of the value than on the target value itself.

IMPLICATION FOR PRACTICE

Reaching a balance in the oxygen administration so as to avoid potential complications associated with hypoxemia or hyperoxemia is a challenge for the clinicians.

IMPLICATION FOR RESEARCH

Further studies on fluctuation of Spo2 comparing different starting targets could better clarify the role of fluctuations and the absolute target values.Video Abstract available at:https://journals.na.lww.com/advancesinneonatalcare/Pages/videogallery.aspx?autoPlay=false&videoId=49.

Effect of electrode temperature on measurements of transcutaneous carbon dioxide partial pressure and oxygen partial pressure in very low birth weight infants

OBJECTIVES

To evaluate the accuracy and safety of measurements of transcutaneous carbon dioxide partial pressure (TcPCO₂) and transcutaneous oxygen partial pressure (TcPO₂) at electrode temperatures lower than the value used in clinical practice in very low birth weight infants.

METHODS

A total of 45 very low birth weight infants were enrolled. TcPCO₂ and TcPO₂ measurements were performed in these infants. Two transcutaneous monitors were placed simultaneously for each subject. One electrode was set and maintained at 42℃ used in clinical practice for neonates (control group), and the other was successively set at 38℃, 39℃, 40°C, and 41℃ (experimental group). The paired t-test was used to compare the measurement results between the groups. A Pearson correlation analysis was used to analyze the correlation between the measurement results of the experimental group and control group, and between the measurement results of experimental group and arterial blood gas parameters.

RESULTS

There was no significant difference in TcPCO₂ between each experimental subgroup (38-41℃) and the control group. TcPCO₂ in each experimental subgroup (38-41℃) was strongly positively correlated with TcPCO₂ in the control group (r>0.9, P<0.05) and arterial carbon dioxide partial pressure (r>0.8, P<0.05). There were significant differences in TcPO₂ between each experimental subgroup (38-41℃) and the control group (P<0.05), but TcPO₂ in each experimental subgroup (38-41℃) was positively correlated with TcPO₂ in the control group (r=0.493-0.574, P<0.05) and arterial oxygen partial pressure (r=0.324-0.399, P<0.05). No skin injury occurred during transcutaneous measurements at all electrode temperatures.

CONCLUSIONS

Lower electrode temperatures (38-41℃) can accurately measure blood carbon dioxide partial pressure in very low birth weight infants, and thus can be used to replace the electrode temperature of 42°C. Transcutaneous measurements at the lower electrode temperatures may be helpful for understanding the changing trend of blood oxygen partial pressure.

Cerebral oxygen saturation and autoregulation during hypotension in extremely preterm infants

BACKGROUND

The impact of the permissive hypotension approach in clinically well infants on regional cerebral oxygen saturation (rScO₂) and autoregulatory capacity (CAR) remains unknown.

METHODS

Prospective cohort study of blinded rScO₂ measurements within a randomized controlled trial of management of hypotension (HIP trial) in extremely preterm infants. rScO₂, mean arterial blood pressure, duration of cerebral hypoxia, and transfer function (TF) gain inversely proportional to CAR, were compared between hypotensive infants randomized to receive dopamine or placebo and between hypotensive and non-hypotensive infants, and related to early intraventricular hemorrhage or death.

RESULTS

In 89 potentially eligible HIP trial patients with rScO₂ measurements, the duration of cerebral hypoxia was significantly higher in 36 hypotensive compared to 53 non-hypotensive infants. In 29/36 hypotensive infants (mean GA 25 weeks, 69% males) receiving the study drug, no significant difference in rScO₂ was observed after dopamine (n = 13) compared to placebo (n = 16). Duration of cerebral hypoxia was associated with early intraventricular hemorrhage or death.  Calculated TF gain (n = 49/89) was significantly higher reflecting decreased CAR in 16 hypotensive compared to 33 non-hypotensive infants.

CONCLUSIONS

Dopamine had no effect on rScO₂ compared to placebo in hypotensive infants. Hypotension and cerebral hypoxia are associated with early intraventricular hemorrhage or death.

IMPACT

Treatment of hypotension with dopamine in extremely preterm infants increases mean arterial blood pressure, but does not improve cerebral oxygenation. Hypotensive extremely preterm infants have increased duration of cerebral hypoxia and reduced cerebral autoregulatory capacity compared to non-hypotensive infants. Duration of cerebral hypoxia and hypotension are associated with early intraventricular hemorrhage or death in extremely preterm infants. Since systematic treatment of hypotension may not be associated with better outcomes, the diagnosis of cerebral hypoxia in hypotensive extremely preterm infants might guide treatment.

Neuroprotection of the Perinatal Brain by Early Information of Cerebral Oxygenation and Perfusion Patterns

Abnormal patterns of cerebral perfusion/oxygenation are associated with neuronal damage. In preterm neonates, hypoxemia, hypo-/hypercapnia and lack of cerebral autoregulation are related to peri-intraventricular hemorrhages and white matter injury. Reperfusion damage after perinatal hypoxic ischemia in term neonates seems related with cerebral hyperoxygenation. Since biological tissue is transparent for near infrared (NIR) light, NIR-spectroscopy (NIRS) is a noninvasive bedside tool to monitor brain oxygenation and perfusion. This review focuses on early assessment and guiding abnormal cerebral oxygenation/perfusion patterns to possibly reduce brain injury. In term infants, early patterns of brain oxygenation helps to decide whether or not therapy (hypothermia) and add-on therapies should be considered. Further NIRS-related technical advances such as the use of (functional) NIRS allowing simultaneous estimation and integrating of heart rate, respiration rate and monitoring cerebral autoregulation will be discussed.

The association between carbon dioxide, cerebral blood flow, and autoregulation in the premature infant

OBJECTIVE

Evaluate the association between carbon dioxide (pCO₂), cerebral blood flow (CBF), and cerebral autoregulation (CA) in preterm infants.

STUDY DESIGN

Cerebral saturations (rScO_2, surrogate for CBF using NIRS) and mean arterial blood pressure (MAP) monitored for 96 h in infants <29 weeks gestation. Relationship between rScO₂, the rScO₂-MAP correlation (CA analysis) and pCO₂ category assessed by mixed effects modeling.

RESULTS

Median pCO₂ differed by postnatal day (p < 0.0001)-pCO₂ increased between day 1 and 2, and low variability seen on day 4. A 5% increase in rScO₂ was noted when pCO₂ was >55 mmHg on each postnatal day (p < 0.001). No association observed between the overall rScO₂-MAP correlation and pCO₂. On day 1 only, the correlation coefficient decreased from 0.26 to -0.09 as pCO₂ category increased (p = 0.02).

CONCLUSIONS

CBF increased above a pCO₂ threshold of 55 mmHg, but overall, no association between pCO₂ and CA was noted.

Early oxygen levels contribute to brain injury in extremely preterm infants

BACKGROUND

Extremely low gestational age newborns (ELGANs) are at risk of neurodevelopmental impairments that may originate in early NICU care. We hypothesized that early oxygen saturations (SpO₂), arterial pO₂ levels, and supplemental oxygen (FiO₂) would associate with later neuroanatomic changes.

METHODS

SpO₂, arterial blood gases, and FiO₂ from 73 ELGANs (GA 26.4 ± 1.2; BW 867 ± 179 g) during the first 3 postnatal days were correlated with later white matter injury (WM, MRI, n = 69), secondary cortical somatosensory processing in magnetoencephalography (MEG-SII, n = 39), Hempel neurological examination (n = 66), and developmental quotients of Griffiths Mental Developmental Scales (GMDS, n = 58).

RESULTS

The ELGANs with later WM abnormalities exhibited lower SpO₂ and pO₂ levels, and higher FiO₂ need during the first 3 days than those with normal WM. They also had higher pCO₂ values. The infants with abnormal MEG-SII showed opposite findings, i.e., displayed higher SpO₂ and pO₂ levels and lower FiO₂ need, than those with better outcomes. Severe WM changes and abnormal MEG-SII were correlated with adverse neurodevelopment.

CONCLUSIONS

Low oxygen levels and high FiO₂ need during the NICU care associate with WM abnormalities, whereas higher oxygen levels correlate with abnormal MEG-SII. The results may indicate certain brain structures being more vulnerable to hypoxia and others to hyperoxia, thus emphasizing the role of strict saturation targets.

IMPACT

This study indicates that both abnormally low and high oxygen levels during early NICU care are harmful for later neurodevelopmental outcomes in preterm neonates. Specific brain structures seem to be vulnerable to low and others to high oxygen levels. The findings may have clinical implications as oxygen is one of the most common therapies given in NICUs. The results emphasize the role of strict saturation targets during the early postnatal period in preterm infants.

Respiratory Monitoring: Current State of the Art and Future Roads

In this article, we present current methodologies, available technologies, and demands for monitoring various respiratory parameters. We discuss the importance of noninvasive techniques for remote and continuous monitoring and challenges involved in the current "smart and connected health" era. We conducted an extensive literature review on the medical significance of monitoring respiratory vital parameters, along with the current methods and solutions with their respective advantages and disadvantages. We discuss the challenges of developing a noninvasive, wearable, wireless system that continuously monitors respiration parameters and opportunities in the field and then determines the requirements of a state-of-the-art system. Noninvasive techniques provide a significant amount of medical information for a continuous patient monitoring system. Contact methods offer more advantages than non-contact methods; however, reducing the size and power of contact methods is critical for enabling a wearable, wireless medical monitoring system. Continuous and accurate remote monitoring, along with other physiological data, can help caregivers improve the quality of care and allow patients greater freedom outside the hospital. Such monitoring systems could lead to highly tailored treatment plans, shorten patient stays at medical facilities, and reduce the cost of treatment.

Near-Infrared spectroscopy for perfusion assessment and neonatal management

Term and preterm infants often present with adverse conditions after birth resulting in abnormal vital functions and severe organ failure, which are associated or sometimes caused by low oxygen and/or blood supply. Brain injury may lead to substantial mortality and morbidity often affecting long-term outcome. Standard monitoring techniques in the NICU focus on arterial oxygen supply and hemodynamics and include respiratory rate, heart rate, blood pressure and arterial oxygen saturation as measured by pulse oximetry but provide only limited information on end organ oxygen delivery. Near-Infrared Spectroscopy can bridge this gap by displaying continuous measurements of tissue oxygen saturation, providing information on the balance of oxygen delivery and consumption in organs of interest. Future techniques using multi-wavelength devices may provide additional information on oxidative metabolism in real time adding important information.

Neurocritical care of premature infants

Neurocritical care is an approach of comprehensive care through multidisciplinary coordination and implementation of neuroprotective strategies to reduce the risk of neurologic injury among critically ill patients. Premature infants are at a special risk of sustaining brain injury and having adverse neurodevelopmental outcome. The pathogenesis of "encephalopathy of prematurity" is tightly linked to hemodynamic instability during postnatal transition, immaturity of the cerebral vascular bed and nervous system, and the commonly encountered inflammation in an intensive care setting. Clinical assessment aided by renewed monitoring techniques, together with therapies supported by best available evidence may provide opportunities to salvage these vulnerable brains. Indeed, to promote optimal brain development and to ensure neurodevelopmental intact survival is of imperial priority in the modern care of preterm infants.

Applying a data-driven approach to quantify EEG maturational deviations in preterms with normal and abnormal neurodevelopmental outcomes

Premature babies are subjected to environmental stresses that can affect brain maturation and cause abnormal neurodevelopmental outcome later in life. Better understanding this link is crucial to developing a clinical tool for early outcome estimation. We defined maturational trajectories between the Electroencephalography (EEG)-derived ‘brain-age’ and postmenstrual age (the age since the last menstrual cycle of the mother) from longitudinal recordings during the baby’s stay in the Neonatal Intensive Care Unit. Data consisted of 224 recordings (65 patients) separated for normal and abnormal outcome at 9–24 months follow-up. Trajectory deviations were compared between outcome groups using the root mean squared error (RMSE) and maximum trajectory deviation (δ^max). 113 features were extracted (per sleep state) to train a data-driven model that estimates brain-age, with the most prominent features identified as potential maturational and outcome-sensitive biomarkers. RMSE and δ^max showed significant differences between outcome groups (cluster-based permutation test, p < 0.05). RMSE had a median (IQR) of 0.75 (0.60–1.35) weeks for normal outcome and 1.35 (1.15–1.55) for abnormal outcome, while δ^max had a median of 0.90 (0.70–1.70) and 1.90 (1.20–2.90) weeks, respectively. Abnormal outcome trajectories were associated with clinically defined dysmature and disorganised EEG patterns, cementing the link between early maturational trajectories and neurodevelopmental outcome.

Do transport factors increase the risk of severe brain injury in outborn infants <33 weeks gestational age?

OBJECTIVE

We evaluated transport factors and postnatal practices to identify modifiable risk factors for SBI.

STUDY DESIGN

Retrospective review of Canadian Neonatal Transport Network data linked to Canadian Neonatal Network data for outborns <33 weeks gestational age (GA), during January 2014 to December 2015. SBI was defined as grade 3 or 4 intraventricular hemorrhage or parenchymal echogenicity, including hemorrhagic and/or ischemic lesions.

RESULT

Among 781 infants, 115 (14.7%) had SBI with range 5.6-40% among transport teams. In multivariable analysis, SBI was associated with GA [0.77 (0.71, 0.85)] per week, receipt of chest compressions and/or epinephrine at delivery [1.81 (1.08, 3.05)] and receipt of fluid boluses [1.61 (1.00, 2.58)].

CONCLUSIONS

Risk factors for SBI were related to the condition at birth and immediate postnatal management and not related to transport factors. These results highlight the importance of maternal transfer to perinatal centers to allow optimization of perinatal management.

N-BiPAP vs n-CPAP in term neonate with respiratory distress syndrome

BACKGROUND

Non-invasive respiratory ventilation has greatly improved the evolution of respiratory distress in neonates, especially for preterm infants, but few studies have investigated the use of non-invasive ventilation (NIV) in term infants. It is useful for neonatologists and nurses to identify the optimal ventilation strategy in terms of effectiveness for this group of newborns. The aim of our study was to investigate what type of respiratory support between nasal Continuous Positive Airway Pressure (nCPAP) or nasal Biphasic Positive Airway Pressure (nBiPAP) is more effective in term neonates with RDS.

METHODS

Our study was a retrospective observational study of 78 full term neonates who were admitted to the NICU at S. Bambino Hospital from December 2015 to December 2016 for respiratory distress at birth. All patients underwent non-invasive ventilation by nCPAP or nBiPAP were included. Oxygen saturations and vital signs were monitored continuously. We evaluated blood gas analysis parameters before treatment and after 1 h of ventilation.

RESULTS

During the study period, there were 78 full term newborns admitted in our NICU for neonatal distress who were treated with nCPAP ore nBIPAP ventilation. In nBiPAP patients, we noticed a statistically significant reduction in PaCO2 levels and FiO2 requirement with respect to nCPAP patients, after 1 h of ventilation with a simultaneous significant increase of pH and PaO2 levels. There was no difference in the length of NIV and hospital stay. Among nCPAP patients, two were then intubated and one developed a pneumothorax.

CONCLUSION

The results of our study showed that an early BiPAP ventilation on RDS is the more efficient NIV because it improves CO2 removal and reduces FiO2 requirement in comparison to nCPAP. Future studies can clarify if early BiPAP ventilation on RDS is the more efficient of NIV.

Effects of Nasal Continuous Positive Airway Pressure on Cerebral Hemodynamics in Preterm Infants

Background: To evaluate the effects of pressure levels on cerebral hemodynamics in premature infants receiving nasal continuous positive airway pressure (nCPAP) during the first 3 days of life. Methods: Forty-four preterm infants treated with nCPAP were divided into two groups: very preterm infants [gestational age 1 (GA1), GA < 32 weeks, n = 24] and moderate/late preterm infants (GA2 group, GA 32-37 weeks, n = 20). During monitoring, pressure levels were set at 4 → 6 → 8 → 4 cmH₂O, and cerebral hemodynamics was assessed by near-infrared spectroscopy (NIRS). Vital signs, peripheral oxygen saturation (SpO₂) and transcutaneous carbon dioxide pressure (TcPCO₂) were simultaneously recorded. Results: Pressures of 4-8 cmH₂O had no significant influence on cerebral hemodynamics, TcPCO₂, SpO₂ or other vital signs. The tissue oxygenation index (TOI), the difference between oxygenated hemoglobin (ΔHbO₂) and deoxygenated hemoglobin (ΔHHb) (ΔHbD), and cerebral blood volume (ΔCBV) were all significantly positively correlated with gestational and post-natal age, with fluctuations being greater in the GA1 group. ΔHbD and ΔCBV were also significantly positively correlated with TcPCO₂. Conclusions: No significant differences were observed in cerebral hemodynamics when the nCPAP pressure was set to 4-8 cmH₂O.

End-tidal carbon dioxide levels during resuscitation and carbon dioxide levels in the immediate neonatal period and intraventricular haemorrhage

Abnormal levels of end-tidal carbon dioxide (EtCO₂) during resuscitation in the delivery suite are associated with intraventricular haemorrhage (IVH) development. Our aim was to determine whether carbon dioxide (CO₂) levels in the first 3 days after birth reflected abnormal EtCO₂ levels in the delivery suite, and hence, a prolonged rather than an early insult resulted in IVH. In addition, we determined if greater EtCO₂level fluctuations during resuscitation occurred in infants who developed IVH. EtCO₂ levels during delivery suite resuscitation and CO₂ levels on the neonatal unit were evaluated in 58 infants (median gestational age 27.3 weeks). Delta EtCO₂ was the difference between the highest and lowest level of EtCO₂. Thirteen infants developed a grade 3-4 IVH (severe group). There were no significant differences in CO₂ levels between those who did and did not develop an IVH (or severe IVH) on the NICU. The delta EtCO₂ during resuscitation differed between infants with any IVH (6.2 (5.4-7.5) kPa) or no IVH (3.8 (2.7-4.3) kPA) (p < 0.001) after adjusting for differences in gestational age. Delta EtCO₂ levels gave an area under the ROC curve of 0.940 for prediction of IVH.Conclusion: The results emphasize the importance of monitoring EtCO₂ levels in the delivery suite.What is Known:• Abnormal levels of carbon dioxide (CO₂) in the first few days after birth and abnormal end-tidal CO₂levels (EtCO₂) levels during resuscitation are associated in preterm infants with the risk of developing intraventricular haemorrhage (IVH).What is New:• There were no significant differences in NICU CO₂levels between those who developed an IVH or no IVH.• There was a poor correlation between delivery suite ETCO₂levels and NICU CO₂levels.• Large fluctuations in EtCO₂during resuscitation in the delivery suite were highly predictive of IVH development in preterm infants.

Metabolic acidosis rather than hypo/hypercapnia in the first 72 hours of life associated with intraventricular hemorrhage in preterm neonates

Aim: Safe limits of arterial partial pressure of carbon dioxide (PaCO₂) and acidosis in premature infants are not well defined. Both respiratory and systemic illness along with center-specific ventilation strategies contribute to PaCO₂ fluctuations and acid-base imbalances during the critical time period of first 72 h of life. This study evaluated the association between early blood gas parameters and intraventricular hemorrhage (IVH) in preterm infants.Methods: This retrospective observational study included neonates with a gestational age (GA) of ≤29 wks, who had at least 7 blood gas analysis done within the first 72 h of life. By adjusting for known variables that predispose to IVH, multivariable logistic regression analysis was used to study the association of PaCO₂ and acid-base measures with the risk of IVH.Results: Between 2013-2016, among 272 neonates who met inclusion criteria and were assessed for IVH on cranial ultrasound within first week of life, 101 neonates [mean GA of 25 ± 1.5 wks] had IVH and 171 neonates [mean GA of 25 ± 1.6 wks] had normal scans. After adjustment for confounding variables, higher values of maximum lactate (OR = 1.18, 95% CI = 1.1-1.3, p < .0001) and maximum base deficit (OR = 1.19, 95% CI = 1.1-1.2, p < .0001) within 72 h of life increased the likelihood of any grade of IVH. However, time-weighted average PaCO₂, maximum and minimum PaCO₂ had no statistically significant effect on the risk of IVH. The relationship remained unchanged even when moderate-severe IVH was considered as the primary outcome.Conclusion: Severe metabolic acidosis rather than hypo/hypercapnia during the first 72 h of life was associated with higher odds of IVH in infants born at ≤29 wks of gestation. Future studies determining levels of PaCO₂ that is safe for premature brain would need to control for the metabolic component of acidosis.

Factors affecting cerebrovascular reactivity to CO2 in premature infants

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.

Continuous Noninvasive Carbon Dioxide Monitoring in Neonates: From Theory to Standard of Care

Ventilatory support may affect the short- and long-term neurologic and respiratory morbidities of preterm infants. Ongoing monitoring of oxygenation and ventilation and control of adequate levels of oxygen, pressures, and volumes can decrease the incidence of such adverse outcomes. Use of pulse oximetry became a standard of care for titrating oxygen delivery, but continuous noninvasive monitoring of carbon dioxide (CO₂) is not routinely used in NICUs. Continuous monitoring of CO₂ level may be crucial because hypocarbia and hypercarbia in extremely preterm infants are associated with lung and brain morbidities, specifically bronchopulmonary dysplasia, intraventricular hemorrhage, and cystic periventricular leukomalacia. It is shown that continuous monitoring of CO₂ levels helps in maintaining stable CO₂ values within an accepted target range. Continuous monitoring of CO₂ levels can be used in the delivery room, during transport, and in infants receiving invasive or noninvasive respiratory support in the NICU. It is logical to hypothesize that this will result in better outcome for extremely preterm infants. In this article, we review the different noninvasive CO₂ monitoring alternatives and devices, their advantages and disadvantages, and the available clinical data supporting or negating their use as a standard of care in NICUs.

Carbon dioxide and retinopathy of prematurity in extremely low birth weight infants

Objective: To evaluate the relationship between partial pressure of carbon dioxide (PCO₂) during the first 3 days of life and retinopathy of prematurity (ROP) in extremely low birthweight (ELBW) infants.Patients and methods: A retrospective evaluation of data on ELBW infants were collected over a period of 4 years. Data during the first 72 hours of life was divided into six, 12-hour epochs. The average highest and overall means of PCO₂, PO₂, FiO_2, and glucose were calculated for each epoch. Logistic regression analysis was used to determine the association between PCO₂ and ROP after controlling for covariables.Results: A total of 78 neonates were included: birth weight (BW) (703 ± 157 g) and gestational age (25 ± 1.4 weeks). A total of 45 out of 78 had ROP: stage 1 (N = 8), stage 2 (N = 26), stage 3 (N = 14), and plus (N = 4). The overall mean PCO₂ correlated with ROP in the first 72 hours of life (R = 0.31, p = .0069). This correlation was significant in epochs 2 (p = .049), 4 (p = .008) and 6 (p = .038). The average of the highest PCO₂ also correlated with ROP in the first 72 hours of life (R = 0.38, p = .0007). This correlation was significant in epochs 2 (p = .0115), 4 (p = .0011), 5 (p = .028) and 6 (p = .037). The correlation between the stage of ROP and PCO₂ was significant after controlling for PO₂ and glucose concentrations. Other variables that correlated with ROP were the overall means of FiO₂ (R = 0.23, p = .04), PO₂ (R = 0.39, p = .0005) and glucose (R = 0.39, p = .0004) as well as the average highest concentrations of FiO₂ (R = 0.26, p = .025), PO₂ (R = 0.38, p = .0008) and glucose (R = 0.34, p = .007).Conclusion: After controlling for confounding variables, ROP correlated with the overall means and average highest PCO₂. ROP also correlated with FiO₂, PO₂ and glucose concentrations. Further studies are needed to define the safe PCO₂ range and the effect of PCO₂ on the normal development of the retina.

Monitoring and management of brain hemodynamics and oxygenation

While cardiorespiratory monitoring is standard for newborns in the NICU, monitoring of brain hemodynamics and oxygenation is usually sporadic and targeted to newborns with suspected or confirmed neurologic disorders. This is unfortunate, since critically ill newborns, both preterm and term-born, are at high risk of brain injury and would benefit from improved techniques for continuous monitoring of brain hemodynamics and oxygenation, in addition to monitoring of systemic hemodynamics and oxygenation. Near-infrared spectroscopy (NIRS) and, to a lesser extent, Doppler ultrasound are techniques that have been used in research and increasingly for clinical purposes to measure and monitor brain hemodynamics and oxygenation in newborns. NIRS monitoring can be useful for detection of diverse pathologic conditions that occur frequently in very preterm newborns and in selected populations of term newborns at risk for brain injury related to disturbances of systemic hemodynamics. This chapter reviews the current state of the art with regard to brain-monitoring techniques and the research directed at this important area, and it concludes with suggestions for the use of currently available tools to manage newborns at high risk of neurologic injury from disturbances in brain hemodynamics and oxygenation.

Monitoring cerebral oxygenation of the immature brain: a neuroprotective strategy?

Monitoring of cerebral oxygenation (rScO₂) with near-infrared spectroscopy (NIRS) is a feasible noninvasive bedside technique in the NICU. This review discusses the possible neuroprotective role of "pattern recognition" of NIRS-derived rScO₂ in preterm neonates with regard to the prevention of severe intraventricular hemorrhage and hypoxia/hyperoxia-related white matter injury. This neuroprotective role of rScO₂ monitoring is discussed as a modality to aid in the early detection of cerebral oxygenation conditions predisposing to these complications. Practical guidelines are provided concerning management of abnormal rScO₂ patterns as well as a brief discussion concerning the need for international consensus and the legal aspects associated with the introduction of a new NICU bedside monitoring strategy.

Interpretation of Cerebral Oxygenation Changes in the Preterm Infant

Near-infrared spectroscopy (NIRS) allows for continuous, non-invasive monitoring of end-organ tissue oxygenation. The use of NIRS, cerebral NIRS (cNIRS) in particular, in neonatal care has increased significantly over the last few years. This dynamic monitoring technique provides real-time information on the cerebral and haemodynamic status of the neonate and has the potential to serve as an important adjunct to patient care with some centres routinely utilising cNIRS to aid decision-making at the bedside. cNIRS values may be influenced by many variables, including cardiac, respiratory and metabolic parameters, and therefore it is essential to understand the pathophysiology behind alterations in cNIRS values. Correct interpretation is required to direct appropriate patient-specific interventions. This article aims to assist clinicians in deciphering cNIRS values by providing an overview of potential causes of fluctuations in cNIRS values, illustrated by common clinical scenarios, with particular emphasis on the preterm infant.

Effects of caffeine on the preterm brain: An observational study

BACKGROUND AND AIM

Caffeine improves neurodevelopmental outcome of preterm infants. This study analyses the effects of caffeine on the neonatal brain. We hypothesized that caffeine has a neuroprotective effect through an increase in oxygen metabolism; reflected by increased cerebral oxygen extraction, electrical function, and perfusion.

METHODS

Preterm infants <32 weeks gestation (GA) receiving their primary dose caffeine-base (10 mg/kg) were included. Ten minutes of stable monitoring were selected before, during, and every hour up to 6 h after caffeine. Near-infrared spectroscopy monitored regional cerebral oxygenation (rScO₂) and extraction (FTOE). Amplitude-integrated electroencephalogram (aEEG) monitored minimum, mean and maximum amplitudes. Spontaneous activity transients (SAT) rate and the interval between SATs (ISI) were calculated. Mean arterial blood pressure (MABP), heart rate (HR) and arterial oxygen saturation (SaO₂) were monitored. Arterial pCO₂'s were collected before and 4 h after caffeine. Brain perfusion was assessed 1 h before and 3 h after caffeine by Doppler-measured resistance-index (RI), peak systolic velocity (PSV) and end-diastolic velocity (EDV), in the anterior cerebral artery (ACA) and internal carotid artery (ICA). Results were presented in mean ± SD.

RESULTS

34 infants, mean GA 28.8 ± 2.1 wk, were included. rScO₂ significantly decreased from 69 ± 11 to 63 ± 12 1 h after caffeine, and recovered at 6 h (66 ± 10). FTOE increased correspondingly. MABP and HR increased significantly. PSV in the ACA decreased slightly. Other Doppler variables, aEEG parameters, and SaO₂ were unaffected.

CONCLUSION

Caffeine increases oxygen extraction, suggesting a (transient) stimulating effect on brain metabolism. However, no substantial changes were found in brain perfusion and in electrical brain activity.

Cerebral oxygen saturation and peripheral perfusion in the extremely premature infant with intraventricular and/or pulmonary haemorrhage early in life

Extremely preterm infants are at higher risk of pulmonary (PH) and intraventricular (IVH) haemorrhage during the transitioning physiology due to immature cardiovascular system. Monitoring of haemodynamics can detect early abnormal circulation that may lead to these complications. We described time-frequency relationships between near infrared spectroscopy (NIRS) cerebral regional haemoglobin oxygen saturation (CrSO₂) and preductal peripheral perfusion index (PI), capillary oxygen saturation (SpO₂) and heart rate (HR) in extremely preterm infants in the first 72 h of life. Patients were sub-grouped in infants with PH and/or IVH (N _H  = 8) and healthy controls (N _C  = 11). Data were decomposed in wavelets allowing the analysis of localized variations of power. This approach allowed to quantify the percentage of time of significant cross-correlation, semblance, gain (transfer function) and coherence between signals. Ultra-low frequencies (<0.28 mHz) were analyzed as slow and prolonged periods of impaired circulation are considered more detrimental than transient fluctuations. Cross-correlation between CrSO₂ and oximetry (PI, SpO₂ and HR) as well as in-phase semblance and gain between CrSO₂ and HR were significantly lower while anti-phase semblance between CrSO₂ and HR was significantly higher in PH-IVH infants compared to controls. These differences may reflect haemodynamic instability associated with cerebrovascular autoregulation and hemorrhagic complications observed during the transitioning physiology.

Investigation of EEG Activity Compared with Mean Arterial Blood Pressure in Extremely Preterm Infants

Background

Cerebral electrical activity in extremely preterm infants is affected by various factors including blood gas and circulatory parameters.

Objective

To investigate whether continuously measured invasive mean arterial blood pressure (BP) is associated with electroencephalographic (EEG) discontinuity in extremely preterm infants.

Study design

This prospective observational study examined 51 newborn infants born <29 weeks gestation in the first 3 days after birth. A single channel of raw EEG was used to quantify discontinuity. Mean BP was acquired using continuous invasive measurement and Doppler ultrasound was used to measure left ventricular output (LVO) and common carotid artery blood flow (CCAF).

Results

Median gestation and birthweight were 25.6 weeks and 760 g, respectively. Mean discontinuity reduced significantly between days 1 and 3. EEG discontinuity was significantly related to gestation, pH and BP. LVO and CCAF were not associated with EEG discontinuity.

Conclusion

Continuously measured invasive mean arterial BP was found to have a negative relationship with EEG discontinuity; increasing BP was associated with lower EEG discontinuity. This did not appear to be mediated by surrogates of systemic or cerebral blood flow. Infants receiving inotropic support had significantly increased EEG discontinuity on the first day after birth.

Preterm infants undergoing laparotomy for necrotizing enterocolitis or spontaneous intestinal perforation display evidence of impaired cerebrovascular autoregulation

BACKGROUND

Preterm infants requiring surgery are at risk of impaired neurocognitive development caused, possibly, by cerebral ischemia associated with impaired cerebrovascular autoregulation (CAR). We evaluated CAR before, during, and after laparotomy.

STUDY DESIGN

This was a hypothesis generating prospective observational cohort study.

SUBJECTS

We included preterm infants requiring surgery for necrotizing enterocolitis (NEC) or spontaneous intestinal perforation (SIP). Before, during, and after surgery we measured cerebral oxygen saturation using NIRS and calculated cerebral fractional tissue oxygen extraction (cFTOE).

OUTCOME MEASURES

Impaired CAR was defined if correlation coefficients (rho) between mean cFTOE and mean arterial blood pressure values were ≤-0.30 with P < .05. We used logistic regression analyses to determine factors associated with impaired CAR.

RESULTS

Nineteen infants with median (IQR) GA 27.6 weeks (26.6-31.0), birth weight 1090 g (924-1430), and postnatal age 9 days (7-12) were included. CAR was impaired more often during surgery than before (12 versus 3, P = .02) or after (12 versus 0, P < .01). A higher PCO₂ level was associated with impaired CAR during surgery (OR 3.04, 95% CI, 1.11-8.12 for every 1 kPa increase).

CONCLUSIONS

More than half of preterm infants with NEC or SIP displayed evidence of impaired CAR during laparotomy. Further research should focus on mechanisms contributing to impaired CAR in preterm infants during surgery.

Influence of PCO2 Control on Clinical and Neurodevelopmental Outcomes of Extremely Low Birth Weight Infants

BACKGROUND

Levels or fluctuations in the partial pressure of CO2 (PCO2) may affect outcomes for extremely low birth weight infants.

OBJECTIVES

In an exploratory analysis of a randomized trial, we hypothesized that the PCO2 values achieved could be related to significant outcomes.

METHODS

On each treatment day, infants were divided into 4 groups: relative hypocapnia, normocapnia, hypercapnia, or fluctuating PCO2. Ultimate assignment to a group for the purpose of this analysis was made according to the group in which an infant spent the most days. Statistical analyses were performed with analysis of variance (ANOVA), the Kruskal-Wallis test, the χ2 test, and the Fisher exact test as well as by multiple logistic regression.

RESULTS

Of the 359 infants, 57 were classified as hypocapnic, 230 as normocapnic, 70 as hypercapnic, and 2 as fluctuating PCO2. Hypercapnic infants had a higher average product of mean airway pressure and fraction of inspired oxygen (MAP × FiO2). For this group, mortality was higher, as was the likelihood of having moderate/severe bronchopulmonary dysplasia (BPD), necrotizing enterocolitis (NEC), and poorer neurodevelopment. Multiple logistic regression analyses showed an increased risk for BPD or death associated with birth weight (p < 0.001) and MAP × FiO2 (p < 0.01). The incidence of adverse neurodevelopment was associated with birth weight (p < 0.001) and intraventricular hemorrhage (IVH; p < 0.01).

CONCLUSIONS

Birth weight and respiratory morbidity, as measured by MAP × FiO2, were the most predictive of death or BPD and NEC, whereas poor neurodevelopmental outcome was associated with low birth weight and IVH. Univariate models also identified PCO2. Thus, hypercapnia seems to reflect greater disease severity, a likely contributor to differences in outcomes.