Neonatal encephalopathy therapy optimization for better neuroprotection with inhalation of CO2: the HENRIC feasibility and safety trial

The Complex Interrelationship Between Mechanical Ventilation and Therapeutic Hypothermia in Asphyxiated Newborns. A Review

Asphyxiated newborns often require both therapeutic hypothermia (TH) and mechanical ventilation (MV) and the complex interrelationship between these two therapeutic interventions is very interesting, which could not only have several synergistic positive effects but also some risks. Perinatal asphyxia is the leading cause of neonatal hypoxic-ischemic encephalopathy (HIE) and TH is the only approved neuroprotective treatment to limit brain injury, improving the mortality rate and long-term neurological outcomes. HIE is often associated with severe respiratory failure, requiring MV, due to different lung diseases or an impairment of the respiratory drive. The respiratory support management of asphyxiated newborns is very difficult, considering (a) various pathophysiological contexts, (b) the strong impact of TH on gas metabolism and (c) on lung mechanics, and (d) complex TH-MV interactions. Therefore, it is necessary to evaluate the real indications of MV for cooled newborns, considering the risks of respiratory overassistance (hypocapnia/hyperoxia), as well as the adequate monitoring systems. To date, specific randomized studies about the optimal respiratory approach for cooled newborns are lacking, and strategies for MV support vary from center to center. Moreover, there are many open questions about the real effects of cooling on lung mechanics and on surfactant, most appropriate method of blood gas analysis, and clear indications for pharmacological sedation. The aim of this review is to propose a reasoned approach for respiratory management of cooled newborns, considering the pathophysiological context, multiple actions of TH, and consequences of TH-MV matched action and its related risks.

Carbon dioxide and MAPK signalling: towards therapy for inflammation

Inflammation, although necessary to fight infections, becomes a threat when it exceeds the capability of the immune system to control it. In addition, inflammation is a cause and/or symptom of many different disorders, including metabolic, neurodegenerative, autoimmune and cardiovascular diseases. Comorbidities and advanced age are typical predictors of more severe cases of seasonal viral infection, with COVID-19 a clear example. The primary importance of mitogen-activated protein kinases (MAPKs) in the course of COVID-19 is evident in the mechanisms by which cells are infected with SARS-CoV-2; the cytokine storm that profoundly worsens a patient's condition; the pathogenesis of diseases, such as diabetes, obesity, and hypertension, that contribute to a worsened prognosis; and post-COVID-19 complications, such as brain fog and thrombosis. An increasing number of reports have revealed that MAPKs are regulated by carbon dioxide (CO2); hence, we reviewed the literature to identify associations between CO2 and MAPKs and possible therapeutic benefits resulting from the elevation of CO2 levels. CO2 regulates key processes leading to and resulting from inflammation, and the therapeutic effects of CO2 (or bicarbonate, HCO3-) have been documented in all of the abovementioned comorbidities and complications of COVID-19 in which MAPKs play roles. The overlapping MAPK and CO2 signalling pathways in the contexts of allergy, apoptosis and cell survival, pulmonary oedema (alveolar fluid resorption), and mechanical ventilation-induced responses in lungs and related to mitochondria are also discussed. Video Abstract.

Hypocarbia is associated with adverse outcomes in hypoxic ischaemic encephalopathy (HIE)

AIM

Hypocarbia in the early postnatal period might exacerbate brain injury in babies with hypoxic ischaemic encephalopathy following birth asphyxia. This mini-review summarised studies on pCO2 values that were monitored periodically in term newborns with moderate/severe hypoxic-ischaemic encephalopathy and correlated with short or long-term outcomes.

METHODS

We searched the databases MEDLINE, EMBASE, Cumulative Index to Nursing and Allied Health Literature (CINAHL), web of science and the Cochrane Library and identified nine studies.

RESULTS

Among the nine included studies, therapeutic hypothermia was administered in seven studies. In most studies, blood pCO2 levels were measured from birth till 72 h of life or till the endpoint of therapeutic hypothermia. Eight studies showed that any hypocarbia (moderate or severe, or cumulative) was associated with an increased risk of adverse outcomes in the form of brain injury in MRI, death or neurodevelopmental disability.

CONCLUSION

Hypocarbia could lead to adverse short-term and long-term outcomes despite therapeutic hypothermia in neonates with HIE. Hence, it is vital to monitor pCO2 levels closely in these infants and consider strategies to maintain pCO2 levels in the normal range.

Hypocapnia in early hours of life is associated with brain injury in moderate to severe neonatal encephalopathy

OBJECTIVE

To evaluate the association between hypocapnia within the first 24 h of life and brain injury assessed by a detailed MRI scoring system in infants receiving therapeutic hypothermia (TH) for neonatal encephalopathy (NE) stratified by the stage of NE.

STUDY DESIGN

This retrospective cohort study included infants who received TH for mild to severe NE.

RESULTS

188 infants were included in the study with 48% having mild and 52% moderate-severe NE. Infants with moderate-severe NE spent more time in hypocapnia (PCO₂ ≤ 35 mmHg) and presented with more severe brain injury on MRI compared to mild cases. The MRI injury score increased by 6% for each extra hour spent in hypocapnic range in infants with moderate-severe NE. There was no association between hypocapnia and injury scores in mild cases.

CONCLUSION

In infants with moderate-severe NE, the hours spent in hypocapnia was an independent predictor of brain injury.

Carbon dioxide levels in neonates: what are safe parameters?

There is no consensus on the optimal pCO₂ levels in the newborn. We reviewed the effects of hypercapnia and hypocapnia and existing carbon dioxide thresholds in neonates. A systematic review was conducted in accordance with the PRISMA statement and MOOSE guidelines. Two hundred and ninety-nine studies were screened and 37 studies included. Covidence online software was employed to streamline relevant articles. Hypocapnia was associated with predominantly neurological side effects while hypercapnia was linked with neurological, respiratory and gastrointestinal outcomes and Retinpathy of prematurity (ROP). Permissive hypercapnia did not decrease periventricular leukomalacia (PVL), ROP, hydrocephalus or air leaks. As safe pCO₂ ranges were not explicitly concluded in the studies chosen, it was indirectly extrapolated with reference to pCO₂ levels that were found to increase the risk of neonatal disease. Although PaCO₂ ranges were reported from 2.6 to 8.7 kPa (19.5-64.3 mmHg) in both term and preterm infants, there are little data on the safety of these ranges. For permissive hypercapnia, parameters described for bronchopulmonary dysplasia (BPD; PaCO₂ 6.0-7.3 kPa: 45.0-54.8 mmHg) and congenital diaphragmatic hernia (CDH; PaCO₂ ≤ 8.7 kPa: ≤65.3 mmHg) were identified. Contradictory findings on the effectiveness of permissive hypercapnia highlight the need for further data on appropriate CO₂ parameters and correlation with outcomes. IMPACT: There is no consensus on the optimal pCO₂ levels in the newborn. There is no consensus on the effectiveness of permissive hypercapnia in neonates. A safe range of pCO₂ of 5-7 kPa was inferred following systematic review.

Impact of Cerebral Oxygen Saturation Monitoring on Short-term Neurodevelopmental Outcomes in Neonates with Encephalopathy - A Prospective Cohort Study

BACKGROUND

Near-infrared spectroscopy (NIRS) has been used for monitoring cerebral oxygen saturation (rSO2) in neonates. There is a lack of data from low-middle income countries (LMIC) setting of cerebral rSO2 in neonates with encephalopathy of diverse etiologies. This study aimed to monitor cerebral rSO2 using NIRS in encephalopathic neonates to maintain the rSO2 between 55 to 85 % in the first 72 hours of admission to improve short-term neurodevelopmental outcomes (NDO).

MATERIALS AND METHODS

This prospective cohort study enrolled encephalopathic neonates with hypoxic- ischemic encephalopathy (HIE) and non-HIE etiologies into 8 clinical categories. The cerebral rSO2 was monitored and targeted to be between 55 to 85 %, with predefined actions and management alterations over 72 hours. The neurodevelopmental assessment was conducted at 3, 6, and 9-12 months corrected age. Moreover, the motor and mental developmental quotients (MoDQ) (MeDQ) were recorded and compared to historical control.

RESULTS

A total of 120 neonates were enrolled and assessed for NDO. The MoDQ (mean ± SD) was 92.55 ± 14.85, 93.80 ± 13.20, 91.02 ± 12.69 and MeDQ (mean ± SD) was 91.80 ± 12.98, 91.80 ± 13.69, 88.41 ± 11.60 at 3, 6 and 9-12 months. The MoDQ and MeDQ scores of the historic cohort at 12 months were 86.35 ± 20.34 and 86.58 ± 18.27. The mean difference [MD (95 %CI)] for MoDQ was - 4.670 (- 8.48 to - 0.85) (p=0.0165) and for MeDQ was - 1.83 (- 5.26 to 1.6) (p=0.29). There was a negative correlation between the composite developmental quotient (CoDQ) with mean rSO2 and a positive correlation with cerebral fractional tissue oxygen extraction (CFTOE). Neonates with HIE and neonatal encephalopathy (NE) (n=37/120) had the lowest motor and mental DQ on neurodevelopmental assessment. Clinical categories, neonatal meningitis (NM), and intraventricular hemorrhage (IVH) improved in DQ scores over the study period.

CONCLUSION

Monitoring and maintaining cerebral rSO2 between 55-85 % through appropriate management changes improved neurodevelopmental scores at the 12-month follow-up in neonates with encephalopathy caused by varied etiologies.

Challenges in respiratory management during therapeutic hypothermia for neonatal encephalopathy

Neonatal encephalopathy (NE) is a serious condition with devastating neurological outcomes that can impact oxygenation and ventilation. The currently recommended therapeutic hypothermia (TH) for these infants may also has several respiratory implications. It decreases metabolic rate and oxygen demands; however, it increases oxygen solubility in the blood and impacts its release to peripheral tissue including the brain. Respiratory management of infants treated with TH should aim for minimizing exposure to hypocapnia or hyperoxia. Inspiratory gas should be heated to 37 °C and humidified to prevent airway and alveolar injury. Blood gas values should be corrected to the core temperature during TH and the use of alkaline buffers is discouraged. While mild sedation/analgesia may ameliorate the discomfort related to cooling, paralytic agents/heavy sedation should be used with caution considering their side effects. Finally, the use of caffeine still needs careful investigation in this population.

Inhaled H2 or CO2 Do Not Augment the Neuroprotective Effect of Therapeutic Hypothermia in a Severe Neonatal Hypoxic-Ischemic Encephalopathy Piglet Model

Hypoxic-ischemic encephalopathy (HIE) is still a major cause of neonatal death and disability as therapeutic hypothermia (TH) alone cannot afford sufficient neuroprotection. The present study investigated whether ventilation with molecular hydrogen (2.1% H₂) or graded restoration of normocapnia with CO₂ for 4 h after asphyxia would augment the neuroprotective effect of TH in a subacute (48 h) HIE piglet model. Piglets were randomized to untreated naïve, control-normothermia, asphyxia-normothermia (20-min 4%O₂–20%CO₂ ventilation; T_core = 38.5 °C), asphyxia-hypothermia (A-HT, T_core = 33.5 °C, 2–36 h post-asphyxia), A-HT + H₂, or A-HT + CO₂ treatment groups. Asphyxia elicited severe hypoxia (pO₂ = 19 ± 5 mmHg) and mixed acidosis (pH = 6.79 ± 0.10). HIE development was confirmed by altered cerebral electrical activity and neuropathology. TH was significantly neuroprotective in the caudate nucleus but demonstrated virtually no such effect in the hippocampus. The mRNA levels of apoptosis-inducing factor and caspase-3 showed a ~10-fold increase in the A-HT group compared to naïve animals in the hippocampus but not in the caudate nucleus coinciding with the region-specific neuroprotective effect of TH. H₂ or CO₂ did not augment TH-induced neuroprotection in any brain areas; rather, CO₂ even abolished the neuroprotective effect of TH in the caudate nucleus. In conclusion, the present findings do not support the use of these medical gases to supplement TH in HIE management.