Effects of severe hypocapnia on expression of bax and bcl-2 proteins, DNA fragmentation, and membrane peroxidation products in cerebral cortical mitochondria of newborn piglets

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.

Hypercapnia Causes Injury of the Cerebral Cortex and Cognitive Deficits in Newborn Piglets

In critically ill newborns, exposure to hypercapnia (HC) is common and often accepted in neonatal intensive care units to prevent severe lung injury. However, as a "safe" range of arterial partial pressure of carbon dioxide levels in neonates has not been established, the potential impact of HC on the neurodevelopmental outcomes in these newborns remains a matter of concern. Here, in a newborn Yorkshire piglet model of either sex, we show that acute exposure to HC induced persistent cortical neuronal injury, associated cognitive and learning deficits, and long-term suppression of cortical electroencephalogram frequencies. HC induced a transient energy failure in cortical neurons, a persistent dysregulation of calcium-dependent proapoptotic signaling in the cerebral cortex, and activation of the apoptotic cascade, leading to nuclear deoxyribonucleic acid fragmentation. While neither 1 h of HC nor the rapid normalization of HC was associated with changes in cortical bioenergetics, rapid resuscitation resulted in a delayed onset of synaptosomal membrane lipid peroxidation, suggesting a dissociation between energy failure and the occurrence of synaptosomal lipid peroxidation. Even short durations of HC triggered biochemical responses at the subcellular level of the cortical neurons resulting in altered cortical activity and impaired neurobehavior. The deleterious effects of HC on the developing brain should be carefully considered as crucial elements of clinical decisions in the neonatal intensive care unit.

Brain-Oriented Strategies for Neuroprotection of Asphyxiated Newborns in the First Hours of Life

Perinatal asphyxia represents the first cause of severe neurological disabilities and the second cause of neonatal death in term-born babies. Currently, no treatment can prevent immediate cell death from necrosis, but some therapeutic interventions, such as therapeutic hypothermia (TH), can reduce delayed cell death from apoptosis. TH significantly improves the combined outcome of mortality or major neurodevelopmental disability, but the number of patients to be treated is 7 to get 1 child with no adverse neurological outcome. The aim of this educational review is to analyze the other care strategies to be implemented to improve the neurological outcome of children with hypoxic ischemic encephalopathy (HIE). Hypocapnia, hypoglycemia, pain control, and functional brain monitoring are recognized as appropriate approaches to improve outcome in critically ill infants with HIE. Pharmacologic neuroprotective adjuncts are currently under investigation. New drugs such as allopurinol and melatonin seem to provide positive effects although more randomized controlled trials are required to establish the effective therapeutic scheme. In the meantime, sustaining the respiratory, metabolic, and cardiovascular system during TH can be a valuable aid in managing and treating the patient with HIE in an optimal way.

Mechanical Ventilation, Partial Pressure of Carbon Dioxide, Increased Fraction of Inspired Oxygen and the Increased Risk for Adverse Short-Term Outcomes in Cooled Asphyxiated Newborns

Neonates treated with therapeutic hypothermia (TH) following perinatal asphyxia (PA) suffer a considerable rate of disability and mortality. Several risk factors associated with adverse outcomes have been identified. Mechanical ventilation might increase the risk for hyperoxia and hypocapnia in cooled newborns. We carried out a retrospective study in 71 asphyxiated cooled newborns. We analyzed the association of ventilation status and adverse short-term outcomes and investigated the effect of the former on pCO₂ and oxygen delivery before, during and after TH. Death, abnormal findings on magnetic resonance imaging, and pathological amplitude-integrated electroencephalography traces were used to define short-term outcomes. The need for mechanical ventilation was significantly higher in the newborns with adverse outcomes (38% vs. 5.6%, p = 0.001). Compared to spontaneously breathing neonates, intubated newborns suffered from significantly more severe asphyxia, had significantly lower levels of mean minimum pCO₂ over the first 6 and 72 h of life (HOL) (p = 0.03 and p = 0.01, respectively) and increased supply of inspired oxygen, which was, in turn, significantly higher in the newborns with adverse outcomes (p < 0.01). Intubated newborns with adverse short-term outcomes had lower levels of pCO₂ over the first 36 HOL. In conclusion, need for mechanical ventilation was significantly higher in newborns with more severe asphyxia. In ventilated newborns, level of encephalopathy, lower pCO₂ levels, and increased oxygen supplementation were significantly higher in the adverse short-term outcomes group. Ventilatory parameters need to be carefully monitored in cooled asphyxiated newborns.

Beyond Anesthesia Toxicity: Anesthetic Considerations to Lessen the Risk of Neonatal Neurological Injury

Infants who undergo surgical procedures in the first few months of life are at a higher risk of death or subsequent neurodevelopmental abnormalities. Although the pathogenesis of these outcomes is multifactorial, an understanding of the nature and pathogenesis of brain injury in these infants may assist the anesthesiologist in consideration of their day-to-day practice to minimize such risks. This review will summarize the main types of brain injury in preterm and term infants and their key pathways. In addition, the review will address key potential pathogenic pathways that may be modifiable including intraoperative hypotension, hypocapnia, hyperoxia or hypoxia, hypoglycemia, and hyperthermia. Each of these conditions may increase the risk of perioperative neurological injury, but their long-term ramifications are unclear.

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

BACKGROUND

There is an association between hypocapnia and adverse neurodevelopmental outcome in infants with neonatal encephalopathy (NE). Our aim was to test the safety and feasibility of 5% CO₂ and 95% air inhalation to correct hypocapnia in mechanically ventilated infants with NE undergoing therapeutic hypothermia.

METHODS

Ten infants were assigned to this open-label, single-center trial. The gas mixture of 5% CO₂ and 95% air was administered through patient circuits if the temperature-corrected PCO₂ ≤40 mm Hg. The CO₂ inhalation was continued for 12 h or was stopped earlier if the base deficit (BD) level decreased <5 mmol/L. Follow-up was performed using Bayley Scales of Infant Development II.

RESULTS

The patients spent a median 95.1% (range 44.6-98.5%) of time in the desired PCO₂ range (40-60 mm Hg) during the inhalation. All PCO₂ values were >40 mm Hg, the lower value of the target range. Regression modeling revealed that BD and lactate had a tendency to decrease during the intervention (by 0.61 and 0.55 mmol/L/h, respectively), whereas pH remained stable. The rate of moderate disabilities and normal outcome was 50%.

CONCLUSIONS

Our results suggest that inhaled 5% CO₂ administration is a feasible and safe intervention for correcting hypocapnia.

Respiratory management during therapeutic hypothermia for hypoxic-ischemic encephalopathy

Therapeutic hypothermia (TH) has become the standard of care treatment to improve morbidity and mortality in infants with hypoxic-ischemic encephalopathy (HIE). Although TH has clearly proven to be beneficial, recent studies suggest optimization of respiratory management as an approach to prevent further damage and improve neurodevelopmental outcome. The ventilatory management of asphyxiated neonates presents a challenge because both the hypoxic insult and TH have an impact on respiratory functions. Although the danger of recurrence of hypocapnia is well recognized, a brief period of severe hyperoxia also can be detrimental to the previously compromised brain and have been shown to increase the risk of adverse neurodevelopmental outcomes. Therefore, judicious ventilatory management with rigorous monitoring is of particular importance in patients with HIE. In the present review, we provide an overview of the currently available evidence on pulmonary function, respiratory morbidities, and ventilation strategies in HIE and we highlight possible future research directions.

Asphyxiated neonates who received active therapeutic hypothermia during transport had higher rates of hypocapnia than controls

AIM

We investigated the association between active hypothermia and hypocapnia in neonates with moderate-to-severe hypoxic-ischaemic encephalopathy (HIE) transported after birth.

METHODS

This was a retrospective cohort study of neonates with HIE born between 2007 and 2011 and transported to Semmelweis University, Hungary, for hypothermia treatment before and after we introduced active cooling during transport in 2009. Of these, 71 received intensive care plus controlled active hypothermia during transport, while the 46 controls just received standard intensive care. Incident hypocapnia was defined as a partial pressure of carbon-dioxide (pCO₂ ) that decreased below 35 mm Hg during transport. Multivariable logistic regression investigated the relationship between hypothermia and incident hypocapnia.

RESULTS

Incident hypocapnia was more frequent in the actively cooled transport group (36.6%) than control group (17.4%; p = 0.025). pCO₂ decreased from a median of 45 to 35 mm Hg (p < 0.0001) in the intervention group, but remained unchanged in the controls. After adjusting for confounders, hypothermia remained an independent risk factor for hypocapnia with an odds ratio (OR) of 4.23 and 95% confidence interval (95% CI) of 1.30-13.79. Sedation was associated with a reduction in OR of hypocapnia, at 0.35 (95% CI 0.12-0.98).

CONCLUSIONS

Hypothermia increased the risk of hypocapnia in neonates with HIE during transport.

Transcutaneous carbon dioxide monitoring for the prevention of neonatal morbidity and mortality

BACKGROUND

Carbon dioxide (CO2) measurement is a fundamental evaluation in a neonatal intensive care unit (NICU), as both low and high values of CO2 might have detrimental effects on neonatal morbidity and mortality. Though measurement of CO2 in the arterial blood gas is the most accurate way to assess the amount of CO2, it requires blood sampling and it does not provide a continuous monitoring of CO2.

OBJECTIVES

To assess whether the use of continuous transcutaneous CO2 (tcCO2) monitoring in newborn infants reduces mortality and improves short and long term respiratory and neurodevelopmental outcomes.

SEARCH METHODS

We used the standard search strategy of the Cochrane Neonatal Review group to search the Cochrane Central Register of Controlled Trials (CENTRAL 2015, Issue 11), MEDLINE via PubMed (1966 to November 1, 2015), EMBASE (1980 to November 1, 2015), and CINAHL (1982 to November 1, 2015). We also searched clinical trials databases, conference proceedings, and the reference lists of retrieved articles for randomized controlled trials and quasi-randomized trials.

SELECTION CRITERIA

Randomized, quasi-randomized and cluster randomized controlled trials comparing different strategies regarding tcCO2 monitoring in newborns. Three comparisons were considered, that is, continuous tcCO2 monitoring versus 1) any intermittent modalities to measure CO2; 2) other continuous CO2 monitoring; and 3) with or without intermittent CO2 monitoring.

DATA COLLECTION AND ANALYSIS

We used the standard methods of the Cochrane Neonatal Review Group. Two review authors independently assessed studies identified by the search strategy for inclusion.

MAIN RESULTS

Our search strategy yielded 106 references. Two review authors independently assessed all references for inclusion. We did not find any completed studies for inclusion, nor ongoing trials.

AUTHORS' CONCLUSIONS

There was no evidence to recommend or refute the use of transcutaneous CO2 monitoring in neonates. Well-designed, adequately powered randomized controlled studies are necessary to address efficacy and safety of transcutaneous CO2 monitoring in neonates.

Hypocarbia and adverse outcome in neonatal hypoxic-ischemic encephalopathy

OBJECTIVE

To evaluate the association between early hypocarbia and 18- to 22-month outcome among neonates with hypoxic-ischemic encephalopathy.

STUDY DESIGN

Data from the National Institute of Child Health and Human Development Neonatal Research Network randomized, controlled trial of whole-body hypothermia for neonatal hypoxic-ischemic encephalopathy were used for this secondary observational study. Infants (n = 204) had multiple blood gases recorded from birth to 12 hours of study intervention (hypothermia versus intensive care alone). The relationship between hypocarbia and outcome (death/disability at 18 to 22 months) was evaluated by unadjusted and adjusted analyses examining minimum PCO(2) and cumulative exposure to PCO(2) <35 mm Hg. The relationship between cumulative PCO(2) <35 mm Hg (calculated as the difference between 35 mm Hg and the sampled PCO(2) multiplied by the duration of time spent <35 mm Hg) and outcome was evaluated by level of exposure (none-high) using a multiple logistic regression analysis with adjustments for pH, level of encephalopathy, treatment group (± hypothermia), and time to spontaneous respiration and ventilator days; results were expressed as odds ratios and 95% confidence intervals. Alternative models of CO(2) concentration were explored to account for fluctuations in CO(2).

RESULTS

Both minimum PCO(2) and cumulative PCO(2) <35 mm Hg were associated with poor outcome (P < .05). Moreover, death/disability increased with greater cumulative exposure to PCO(2) <35 mm Hg.

CONCLUSIONS

Hypocarbia is associated with poor outcome after hypoxic-ischemic encephalopathy.

To autoregulate or not to autoregulate--that is no longer the question

In the late 1970s, high cerebral blood flow was perceived as a cause of intracranial hemorrhage in the preterm infant. Intracranial hemorrhage was diagnosed by computed tomography and ultrasound found to be frequent not only in babies who died. Hemorrhage was soon linked to cerebral palsy in survivors. The analogy was hypertensive hemorrhagic stroke in the adult. Cerebral hemorrhage was perceived as the major (preventable) cause of brain injury in the preterm baby. An immature cerebral autoregulation or a vulnerability of the autoregulation exposed by preceding hypoxia or ischemia therefore became a focus of neonatal brain research in the 1980s. Over the years the focus has changed, first to the pathogenesis of hypoxic-ischemic brain injury, then to the effects of pCO(2), and now 30 years later to a more comprehensive, less clearly hypothesis-driven exploration of the multitude of factors involved in cerebral blood flow and oxygenation. Meanwhile, some basic questions regarding autoregulation remain unanswered, and some concepts from the 1970s still direct clinical practice.

Lipopolysaccharide induces apoptosis in Carassius auratus lymphocytes, a possible role in pathogenesis of bacterial infection in fish

Lipopolysaccharide (LPS), the endotoxin of Gram-negative bacteria, is capable of eliciting a wide variety of pathophysiological effects, including endotoxin shock, tissue injury and lethality in both humans and animals. It is also a potent stimulant to initiate the proliferation, differentiation and activation of B lymphocytes and macrophages, resulting in changes of inflammatory cytokines, such as TNF-alpha, IL1-beta, IL6, IL-8 and IL-12, and enhancement of immune responses. However, little is known about its effect on the induction of apoptosis in lymphocytes. In the present study, the lymphocytes from Carassius auratus were employed for this purpose. The cells were exposed to LPS at various doses for different time periods. By careful apoptotic characteristic analysis, such as condensation of nuclear chromatin, fragmentation of genomic DNA and formation of apoptotic bodies, it provided the first evidence that LPS had apoptotic-inducing effect on fish lymphocytes in a time- and dose-dependent manner. LPS exposure induced significant increase of intracellular reactive oxygen species (ROS), loss of mitochondrial transmembrane potential (DeltaPsi), depletion of ATP production, down-regulation of Bcl-2 expression, up-regulation of Bax and mitochondrial NO-synthase (mNOS) expression, and selective activation of caspase-9 rather than caspase-8. Each of these observations suggests that the LPS-induced apoptosis in C. auratus lymphocytes occurs largely via the mitochondrial apoptotic pathway. This observation was different from the mechanism behind the LPS-induced apoptosis in mammalian macrophages/thymocytes that occurs via the TNF-alpha-mediated death-receptor pathway. Our study suggested the existence of a possible novel role in the pathogenesis of Gram-negative bacterial infection in fish and even in mammals, which may contribute to the therapy of bacterial diseases. Also, it will help to gain more insights into the mechanisms of septic shock and of LPS-induced immunosuppression and autoimmunity.