Hypoxic-Ischemic Encephalopathy in the Term Infant Jeffrey M Perlman MB Prof

1. Hypoxic-Ischemic Encephalopathy in the Term Infant Jeffrey M Perlman MB Professor of Pediatrics Weill Medical College Cornell Medical Center New York

2. Background • Hypoxic-ischemic brain injury that occurs during the perinatal period remains the most prominent cause of neonatal mortality and long term neurologic morbidity often referred to as cerebral palsy. • It is noted in approximately 1 to 2 per 1000 deliveries. • An understanding of the pathogenesis of injury is critical prior to the implementation of targeted interventions.

3. Outline • Pathogenesis • Adaptative fetal mechanisms • Identification of High risk Infants • Treatment strategies Delivery room - room air versus 100% O2 Beyond the delivery room - supportive care - neuroprotective strategies

4. Pathogenesis Impaired cerebral blood flow (CBF) is the principal pathogenetic mechanism underlying most of the neuropathology attributed to perinatal brain injury. It is most likely to occur as a consequence of interruption of placental blood flow and gas exchange; a state that is referred to as asphyxia.

5. Definitions • Hypoxia - refers to an abnormal reduction in oxygen delivery to the tissue • Ischemia - refers to a reduction in blood flow to the tissue • Asphyxia - refers to progressive hypoxia, hypercarbia and acidosis. However the biochemical definition of what constitutes asphyxia is imprecise - a cord pH < 7.00 is defined as pathologic or severe fetal acidemia.

6. Characteristics of Hypoxic-Ischemic Brain Damage • Hypoxic-ischemic brain injury is an evolving process that begins during the insult and extends into a recovery period - reperfusion period • Tissue injury takes the form of : Necrosis - characterized by tissue swelling, membrane disruption and an inflammatory cellular response or Apoptosis “programmed cell death” characterized by cellular and nuclear shrinkage, chromatin condensation and DNA fragmentation. • A severe insult results in necrosis and a less severe and prolonged insult in apoptosis

7. Electron microscopic images of dying neurons in neocortex from an infant rat 48 hours after hypoxia-ischemia Necrotic neuron with chromatin dispersed into numerous small irregular shaped structures and disrupted nuclear and cytoplasmic membranes Apoptotic neuron with one large apoptotic body including condensed chromatin

8. Pathogenesis of Hypoxic-Ischemic Cerebral Injury Interruption of Placental Blood Flow Acute Intermittent Hypoxia-Ischemia Resuscitation In-utero Postnatal Reperfusion Injury

9. Effects of Hypoxia-Ischemia on Carbohydrate and Energy Metabolism-Anaerobic Glycolysis •  Brain Glycogen •  Lactate production •  Phosphocreatine •  Brain Glucose •  ATP • Tissue acidosis

10. Adenosine Triphosphate (ATP) • Critical regulator of cell function because of its role in energy transformation. • One major function is to preserve ionic gradients across plasma and intracellular membranes, i.e., Na , K , Ca   • Ionic pumping utilizes 50-60% of total cellular expenditure

11. Ischemia Anaerobic Glycolysis  PCr  ATP  Lactate [Na+]out [K+] out [Ca++] in

12. Deleterious Effects of Calcium in Hypoxia-Ischemia • Activates phospholipases membrane injury • Activates proteases cytoskeleton degraded • Activates nucleases DNA breakdown • Uncouples oxidative phosphorylation  ATP •  neurotransmitter release i.e. glutamate • Activates NOS generates nitric oxide

13. Additional Mediators of Cell Death During and Following Hypoxia-Ischemia (HI) • Free radicals - highly reactive compounds - can react with certain cellular constituents e.g. membrane lipids generating more radicals and thus a chain reaction with irreversible biochemical injury. • Glutamate - Excitatory amino acid acts on NMDA receptors to facilitate intracellular Ca++ entry and delayed cell death - Glutamate accumulates during HI in part because of  reuptake that requires ATP

14. Potential Mechanisms of Injury Following Hypoxia-Ischemia HYPOXIA-ISCHEMIA ANAEROBIC GLYCOGLYSIS ATP ADENOSINE GLUTAMATE LACTATE NMDA RECEPTOR HYPOXANTHINE INTRACELLULAR Ca+ XANTHINE OXIDASE ACTIVATES NOS ACTIVATES LIPASES XANTHINE FREE FATTY ACIDS O2 NITRIC OXIDE O2 FREE RADICALS FREE RADICALS FREE RADICALS

15. Calcium NOS Nitric Oxide Peroxynitrite Mitochondria Cytochrome C Caspace Energy Failure DNA Fragmentation Nuclear /Cytoplasmic Breakdown Apoptosis Necrosis

16. Delayed Injury - Reperfusion Injury • Following resuscitation cerebral oxygenation and perfusion is restored. During this initial recovery phase, the concentration of the phosphorus metabolites (ATP) and intracellular pH returns to baseline. • However the process of cerebral energy failure recurs from 6 to 48 hours later in a secondary phase of injury. This phase is characterized by a decrease in phosphocreatinine although the intracellular pH remains normal. Moreover this phase occurs despite stable cardio-respiratory status From Lorek et al Pediatr Res 1994

17. Pathogenesis of Hypoxic-Ischemic Cerebral Injury Interruption of Placental Blood Flow Acute Intermittent Hypoxia-Ischemia Resuscitation In-utero Postnatal Reperfusion Injury

18. Mechanisms of Reperfusion Injury • The mechanisms of secondary energy failure likely secondary to extended reactions from the primary insults e.g. calcium influx, excitatory neurotoxicity, free radicals and nitric oxide formation adversely alters mitochondrial function. • Recent evidence suggests that circulatory and endogenous inflammatory cells/mediators also contribute to the ongoing injury. • These processes result in apoptotic cell death.

19. Infection and/or the fetal inflammatory response as a potential contributing factor to brain injury during hypoxia-ischemia

20. IL-6, IL-8, RANTES IN CORD BLOOD: CONTROL VS CHORIO Control Chorio *p <0.05

21. CHANGES IN IL-6 OVER THE FIRST 36 HRS IN CHORIOAMNIONITIS INFANTS

22. IL-6 AND MODIFIED DUBOWITZ SCORES AT 6 HOURS OF AGE IN CHORIO INFANTS

23. IL-6, IL-8, RANTES:No HIE vs HIE

24. CONCLUSIONS • In infants exposed to chorioamnionitis, there was a spectrum of abnormalities in the neurological exam from normal, to transient hypotonia, to HIE • IL-6, IL-8 and RANTES were significantly elevated in all infants with Chorio as compared to controls - IL6 at 6 hours were correlated with hypotonia by Modified Dubowitz Scores - IL6, IL8 and RANTES at 6 hrs were highest in infants that developed HIE and/or seizures

25. SPECULATION Chorioamnionitis Hypotonia HIE / Seizures CYTOKINES

26. Potential Mechanisms of Injury Following Hypoxia-Ischemia HYPOXIA-ISCHEMIA ANAEROBIC GLYCOGLYSIS ATP ADENOSINE GLUTAMATE LACTATE NMDA RECEPTOR HYPOXANTHINE INTRACELLULAR Ca+ XANTHINE OXIDASE ACTIVATES NOS ACTIVATES LIPASES XANTHINE FREE FATTY ACIDS O2 NITRIC OXIDE O2 FREE RADICALS FREE RADICALS FREE RADICALS

27. HYPOXIA-ISCHEMIA ANAEROBIC GLYCOGLYSIS ATP ADENOSINE GLUTAMATE LACTATE IL- TNF- NMDA RECEPTOR HYPOXANTHINE IL- TNF- Interferon  INTRACELLULAR Ca+ XANTHINE OXIDASE ACTIVATES NOS ACTIVATES LIPASES XANTHINE FREE FATTY ACIDS O2 NITRIC OXIDE O2 FREE RADICALS FREE RADICALS FREE RADICALS

28. Foundation Fact Although interference in placental blood flow and consequently gas exchange is fairly common, residual neurologic sequelae are infrequent and are more likely to occur when the asphyxial event is severe.

29. WHY? The fetus immediately adapts to an asphyxial event to preserve cerebral blood flow and oxygen delivery. This adaptation includes both circulatory and non circulatory responses.

30. ASPHYXIA (PaO2, PaCO2,pH) Redistribution of Cardiac Output Cerebral, Coronary, Adrenal Renal, Intestinal Blood Flow Blood Flow Ongoing Asphyxia Cardiac Output Cerebral Blood Flow CARDIOVASCULAR RESPONSES TO ASPHYXIA

31. ADAPTIVE MECHANISMS ASSOCIATED WITH ASPHYXIA TO MAINTAIN CEREBRAL PERFUSION • Circulatory Responses • Non-circulatory Responses

32. NON-CIRCULATORY RESPONSES FACTOR CONTRIBUTING TO NEURONAL PRESERVATION • Slower depletion of high energy compounds. • Use of alternate energy substrate - the neonatal brain has the capacity to use lactate and ketone bodies for energy production. • The relative resistance of the fetal and neonatal myocardium to hypoxia ischemia. • Potential protective role of fetal hemoglobin.

33. Foundation Fact • The ability to identify infants at highest risk for progressing to hypoxic-ischemic encephalopathy is critical for two reasons a)The therapeutic window i.e. that time whereby intervention strategies may be effective in preventing the processes of ongoing injury in the newborn brain is short and considered to be less than six hours b) Novel therapeutic strategies to prevent ongoing injury have the potential for significant side effects

34. Early Identification of High Risk Infants 1) Evidence of an Acute Perinatal Insult Indicated by a combination of markers* 1) Sentinel event 2) Delivery room resuscitation 3) 5 Minute Apgar score  5 4) Cord arterial pH  7.00 + 2) Postnatal evidence of encephalopathy 1) Clinical 2) EEG * Sensitivity (80%), Specificity 98%, Positive Predictive value (50%) Perlman & Risser Pediatrics 97,1996

35. Clinical: Assessment of Encephalopathy Staging of Encephalopathy Stage 1 - Mild Stage 2 - Moderate Stage3 - Severe Neurologic Evaluation Level of Consciousness Neuromuscular control Reflexes Autonomic function Evidence of Seizures Sarnat Arch of Neurol. 33;696,1976

36. DeathDisability Mild 0 0 Moderate 6% 30% Severe 60% 100% Long term outcome of term infants with Perinatal Hypoxic-Ischemic Encephalopathy

37. a-EEG: Assessment of Cerebral Function A Cerebral Function Monitor via a single channel EEG (a-EEG), records activity from two biparietal electrodes. The signal is smoothed and the amplitude integrated. Three distinct patterns of electrical activity are noted i.e. normal, moderate and severe suppression. Early evidence of moderate and/or severe suppression identifies abnormal neurologic outcome with a sensitivity of 100%, positive predictive value of 85% and negative predictive value of 100%. Naqeeb, et al. Pediatrics 1999:103:1263

38. Representative aEEG tracings Normal Moderate Suppression Severe Suppression

39. Abnormalities in both the Clinical and a-EEG evaluation enhances the early detection of infants who progress to irreversible brain injury. Study Criteria* 1) 50 infants with an acute perinatal insult 2) Clinical examination within 6 hours- Abnormal = Sarnat stage 2 or 3 encephalopathy 3) Simultaneous a-EEG assessment Abnormal = Moderate or severe suppression 4) Persistent encephalopathy > 5 days was the outcome of interest- this developed in 14/50 infants * Shalak et al Pediatrics in press

40. Prediction of Persistent Encephalopathy (n=14) based oneither an abnormal clinical or a-EEG evaluation, or a combination of abnormalities in both Test N S SP PPV NPV Abnormal Exam 19 78% 78% 58% 90% Abnormal EEG 1589% 73% 91% 91% Both Abnormal 1378% 94% 85% 92% N=number potentially enrolled in a study, S= sensitivity SP=specificity PPV=positive predictive value, NPV=negative predictive value

41. Management of the Infant at Risk for Hypoxic - Ischemic Cerebral Injury • Delivery Room • Beyond the Delivery Room

42. HYPOXIA-ISCHEMIA ANAEROBIC GLYCOGLYSIS ATP ADENOSINE GLUTAMATE LACTATE NMDA RECEPTOR HYPOXANTHINE INTRACELLULAR Ca+ XANTHINE OXIDASE ACTIVATES NOS ACTIVATES LIPASES XANTHINE FREE FATTY ACIDS O2 NITRIC OXIDE O2 FREE RADICALS FREE RADICALS FREE RADICALS

43. Room Air (RA)versus 100% O2 • There is considerable debate whether to use RA versus 100% during DR resuscitation. This is highly relevant given the importance of free radicals in the genesis of ongoing injury. • Studies indicate that RA versus 100% O2 during DR resuscitation in term infants appears to be comparable with regard to short term outcome measures i.e. encephalopathy and /or death within 7 days Ramji et al Pediatr Res 1993;34:809, Saugstad etal Pedaitrics 1998;102;e1

44. ) • Infants n=40 and >36 weeks with “Asphyxia” - umbilical PaO2 < • 70 mmHg PaCO2 > 60 mmHg pH < 7.15 and clinical - hypotonia, apnea, • bradycardia (<80BPM) were randomly resuscitated with RA or 100% O2. • RA vs O2 group needed • a)  time to first cry (1.2  0.6 vs 1.7  .05 min) • b)  time to regular respiratory pattern (4.6  0.7 vs 7.5  1.8 m) • c)  reduced-to-oxidized- glutathione ratio Room Air (RA) versus 100% O2- new data Vento et al Resuscitation with room air instead of 100% oxygen prevents oxidative stress in moderately asphyxiated term neonates. Pediatrics 107;642-647:2001

45. Management Beyond the Delivery Room • General Measures • Neuroprotective Strategies

46. Management Beyond the Delivery Room-General Measures • Ventilation • Fluid Status • Oliguria • Hypotension • Glucose status • Seizures • Cerebral edema

47. Role of Glucose • Both hyper and hypoglycemia may be seen in the post resuscitative phase. • Both may exacerbate neuronal injury • Hyperglycemia may contribute to  levels of lactate and thus to continuing acidosis • Hypoglycemia may contribute to injury particularly in parieto-occipito cortex • The goal should be to maintain glucose levels in the normal range

48. Characteristics of Infants with a Blood Sugar < 40mg/dl versus Infants with a Blood Sugar > 40mg/dl Salhab et al Pediatrics 114 361.2004

49. Salhab et al Pediatrics 114 361.2004

50. Salhab et al Pediatrics 114 361.2004