Bench to bedside strategies for optimizing neuroprotection following perinatal hypoxia-ischaemia in high and low resource settings

The factors affecting neurodevelopmental outcomes in HIE

BACKGROUND

Hypoxic ischemic encephalopathy (HIE) has different neurological outcomes.

AIM

We wanted to see if there was any developmental delay in neonates with hypoxia ischemic encephalopathy who were given therapeutic hypothermia.

STUDY DESIGN

Retrospective cohort study.

METHODS

The Denver developmental screening test II (DDST-II) was performed to newborns who had been applied to therapeutic hypothermia.

RESULTS

There were 69 male and 36 female newborns. The mean 1-min and 5-min Apgar scores were 4.72 ± 2.51 and 7.03 ± 2.017, respectively. The mean pH and mean base excess were 6.92 ± 0.1 and -18.05 ± 5.72, respectively. The most common risk factors were meconium staining (17.1%). There were 67 patients with Stage I, 20 with Stage II, and 18 with Stage III. Diffusion restriction was seen in 13 patients. 28 patients had seizures. In aEEG, 12 patients had burst suppression. Three (2.9%) infants died during hospitalization. 19 patients missed follow-up appointments. Thirteen patients had abnormal development according to DDST-II. Seven patients had gross motor function delays and were diagnosed with cerebral palsy. Three had language skill delays, but two of them had speech disorders after two years of age. Two had delayed milestones. Two had delays in fine motor skills but did not have any sequels after two years of age. A significant difference was found between seizures and the severity of Sarnat stage, intubation in the delivery room with developmental delay. Apgar scores were significantly lower in patients with CP.

CONCLUSION

We should closely follow-up neonates who had low Apgar scores, seizures, a high Sarnat stage, were intubated in the delivery room.

Neonatal Hypoxia Ischaemia: Mechanisms, Models, and Therapeutic Challenges

Neonatal hypoxia-ischaemia (HI) is the most common cause of death and disability in human neonates, and is often associated with persistent motor, sensory, and cognitive impairment. Improved intensive care technology has increased survival without preventing neurological disorder, increasing morbidity throughout the adult population. Early preventative or neuroprotective interventions have the potential to rescue brain development in neonates, yet only one therapeutic intervention is currently licensed for use in developed countries. Recent investigations of the transient cortical layer known as subplate, especially regarding subplate's secretory role, opens up a novel set of potential molecular modulators of neonatal HI injury. This review examines the biological mechanisms of human neonatal HI, discusses evidence for the relevance of subplate-secreted molecules to this condition, and evaluates available animal models. Neuroserpin, a neuronally released neuroprotective factor, is discussed as a case study for developing new potential pharmacological interventions for use post-ischaemic injury.

Temperature profile and outcomes of neonates undergoing whole body hypothermia for neonatal hypoxic-ischemic encephalopathy

BACKGROUND

Decreases below the target temperature were noted among neonates undergoing cooling in the Eunice Kennedy Shriver National Institute of Child Health and Human Development Neonatal Research Network Trial of whole body hypothermia for neonatal hypoxic-ischemic encephalopathy.

OBJECTIVE

To examine the temperature profile and impact on outcome among ≥ 36 wk gestation neonates randomized at ≤ 6 hrs of age targeting an esophageal temperature of 33.5°C for 72 hrs.

DESIGN, SETTING, PATIENTS

Infants with intermittent temperatures recorded of <32.0°C during induction and maintenance of cooling were compared to all other cooled infants, and the relationship with outcome at 18 months was evaluated.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

There were no differences in the stage of encephalopathy, acidosis, or 10 min Apgar scores between infants with temperatures of <32.0°C during induction (n = 33) or maintenance (n = 10) and all other infants who were cooled (n = 58); however, birth weight was lower and the need for blood pressure support higher among infants with temperatures of <32.0°C compared to all other cooled infants. No increase in acute adverse events was noted among infants with temperatures of <32.0°C, and hours spent at <32°C was not associated with the primary outcome of death or moderate/severe disability or the Bayley II Mental Developmental Index at 18 months.

CONCLUSIONS

Term infants with a lower birth weight are at risk for decreasing temperatures of <32.0°C while undergoing body cooling using a servo-controlled system. This information suggests extra caution during the application of hypothermia as these lower birth weight infants are at risk for overcooling. Our findings may assist in planning additional trials of lower target temperature for neonatal hypoxic-ischemic encephalopathy.

Filling the evidence gap: how can we improve the outcome of neonatal encephalopathy in the next 10 years?

Neonatal encephalopathy associated with perinatal hypoxia-ischaemia is one of the most common causes of death and permanent disability worldwide. However, of a wide range of "experimentally neuroprotective treatments" invented so far, only therapeutic hypothermia has been promoted into a standard clinical practice. Such a wide gap in the efficacy of neuroprotective treatments between the experimental setting and clinical practice may be attributed to the strategic flaw in translating basic knowledge into clinical care. When previous clinical studies are carefully reviewed, one may notice that few therapeutic options were chosen based on their track records in experimental studies; protective effects of some drugs had been assumed only based on their pharmacokinetics in adult species; several therapies were chosen merely because clinicians were familiar to these treatments for other purpose; some other therapies were imported too preliminarily from laboratory to clinical practice, potentially ignoring the difference in physiological and pathological backgrounds between rodent models and human patients. When further clinical trials are planned, it is important to ask whether (i) the treatment is supported by pharmacokinetics specific to immature brain, and (ii) the neuroprotective effect of the treatment has consistently been demonstrated using clinically relevant models and study designs. The use of translational large animal models allows the practical simulation and fine-tuning of clinical protocols, which may further assist successful translation of basic knowledge. In addition to the effort to develop alternative therapeutic options, it is important to maximise the effect of the current only neuroprotective option, or therapeutic hypothermia. Independent variables which influence the efficacy of hypothermia have to be elucidated to improve its therapeutic protocol, and to increase the number of patients who will benefit from this treatment.

The pig as a model animal for studying cognition and neurobehavioral disorders

In experimental animal research, a short phylogenetic distance, i.e., high resemblance between the model species and the species to be modeled is expected to increase the relevance and generalizability of results obtained in the model species. The (mini)pig shows multiple advantageous characteristics that have led to an increase in the use of this species in studies modeling human medical issues, including neurobehavioral (dys)functions. For example, the cerebral cortex of pigs, unlike that of mice or rats, has cerebral convolutions (gyri and sulci) similar to the human neocortex. We expect that appropriately chosen pig models will yield results of high translational value. However, this claim still needs to be substantiated by research, and the area of pig research is still in its infancy. This chapter provides an overview of the pig as a model species for studying cognitive dysfunctions and neurobehavioral disorders and their treatment, along with a discussion of the pros and cons of various tests, as an aid to researchers considering the use of pigs as model animal species in biomedical research.

Potential biomarkers for hypoxic-ischemic encephalopathy

Cerebral hypothermia reduces brain injury and improves behavioral recovery after hypoxia-ischemia (HI) at birth. However, using current enrolment criteria many infants are not helped, and conversely, a significant proportion of control infants survive without disability. In order to further improve treatment we need better biomarkers of injury. A 'true' biomarker for the phase of evolving, 'treatable' injury would allow us to identify not only whether infants are at risk of damage, but also whether they are still able to benefit from intervention. Even a less specific measure that allowed either more precise early identification of infants at risk of adverse neurodevelopmental outcome would reduce the variance of outcome of trials, improving trial power while reducing the number of infants unnecessarily treated. Finally, valid short-term surrogates for long term outcome after treatment would allow more rapid completion of preliminary evaluation and thus allow new strategies to be tested more rapidly. Experimental studies have demonstrated that there is a relatively limited 'window of opportunity' for effective treatment (up to about 6-8h after HI, the 'latent phase'), before secondary cell death begins. We critically evaluate the utility of proposed biochemical, electronic monitoring, and imaging biomarkers against this framework. This review highlights the two central limitations of most presently available biomarkers: that they are most precise for infants with severe injury who are already easily identified, and that their correlation is strongest at times well after the latent phase, when injury is no longer 'treatable'. This is an important area for further research.

Protecting motor networks during perinatal ischemia: the case for delta-opioid receptors

Perinatal ischemia is a common clinical problem with few successful therapies to prevent neuronal damage. Delta opioid receptor (DOR) activation is a versatile, evolutionarily conserved, endogenous neuroprotective mechanism that blocks several steps in the deleterious cascade of neurological events during ischemia. DOR activation prior to ischemia or severe hypoxia is neuroprotective in spinal motor networks, as well as cortical, cerebellar, and hippocampal neural networks. In addition to providing acute and long-lasting neuroprotection against ischemia, DOR activation appears to provide neuroprotection when given before, during, or following the onset of ischemia. Finally, DORs can be upregulated by several physiological and experimental perturbations. Potential adverse side effects affecting motor control, such as respiratory depression and seizures, are not well established in young mammals and may be mitigated by altering drug choice and method of drug administration. The unique features of DOR-dependent neuroprotection make it an attractive potential therapy that may be given to at-risk pregnant mothers shortly before delivery to provide long-lasting neuroprotection against unpredictable perinatal ischemic events.

Neuroprotection in infant heart surgery

Neonatal hypoxic-ischemic encephalopathy, prematurity, sepsis-meningitis, and serious forms of complex congenital heart disease requiring infant heart surgery are just a few examples of disorders that share high mortality and morbidity rates. Newborn heart surgery represents a period of planned and deliberate ischemia-reperfusion injury, which is obliged to occur to cure or palliate complex forms of congenital heart disease. Advances in cardiothoracic surgical and anesthetic techniques, including cardiopulmonary bypass and deep hypothermic circulatory arrest, have substantially decreased mortality, expanding the horizon to address functional neurologic and cardiac outcomes in long-term survivors. Interest in the functional status of survivors now stretches beyond the newborn period to childhood, adolescence, and adulthood.