Neurology - Therapeutic Hypothermia & HIE Flashcards
HIE
Hypoxic-Ischaemic Encephalopathy
- Neurological grey matter injury caused by O2 deprivation (hypoxia) and reduced blood flow (ischaemia) to the brain
- Leads to cell death, seizures, long-term developmental impairments
Causes of HIE
Before labour:
- Placental insufficiency
- Severe maternal hypoxia (cardiac arrest, anaemia)
- Infections
- CHDs
During labour/delivery:
- Umbilical cord prolapse
- Placental abruption
- Meconium Aspiration Syndrome (MAS)
After birth:
- Respiratory failure
- Sepsis
- Meningitis
- Severe hypoglycaemia
Phases of the mechanism of HIE
- Primary Energy Failure - initial hypoxia/ischaemia
- Latent Phase - 6h post-injury
- Secondary Energy Failure - 6-72h post-injury
- Tertiary Phase - weeks to years post-injury
First phase of the mechanisms of HIE
Primary Energy Failure - Initial hypoxia/ischaemia:
- ↓ O2 and glucose leading to ATP depletion, ↑ anaerobic metabolism and ↑ lactate
- Lactate buildup prevents regular flow of ions leading to cellular oedema
- Excitotoxicity causing free radical damage
Second phase of the mechanisms of HIE
Latent phase - 6h post-injury
Transient recovery of ATP, cells begin to stabilise but damage continues - reperfusion injury as blood rushes in.
- Determines severity of injury, prognosis, TH protocol occurs
Third phase of the mechanisms of HIE
Secondary Energy Failure - 6-72h post-injury:
- Mitochondrial dysfunction causing inflammation + apoptosis
- Brain swelling, seizures, oxidative stress (irreversible damage)
Fourth phase of the mechanisms of HIE
Tertiary Phase - weeks to years later:
- Ongoing neuro-inflammation
- Long-term neurological remodelling and functional deficits
Asphyxia
An impairment in the exchange of respiratory gases - placenta not functioning correctly to facilitate this before the baby’s first breath when their lungs can begin to function
Diagnosing HIE
- Hx of pregnancy, labour, asphyxia, resuscitation
- Apgar score
- Arterial blood gases - cord gases and from baby within first hour of life
4.Physical exam (Sarnat scoring)
How blood gases determine the severity of hypoxia
The more lactate is present in blood - the longer the baby went w/o O2
The lower the pH of the cord blood - the more acidotic the baby is (<7 indicates candidate for cooling)
Base deficit value = how much alkalinity needs to be added to get the pH to 7.4 (> -16mmol/L indicates candidate for cooling)
Sarnat scoring system
Physical Exam to diagnose HIE
HIE Stage 1 Mild: Hyper-alertness (high HR, normal EEG, active reflexes)
HIE Stage 2 Moderate: Lethargic (sleepy, hypotonic - ↓ muscle tone, weak reflexes, low HR, periodic breathing, seizures, burst suppression and background slowing EEG)
HIE Stage 3 Severe: Coma (flaccid tone, absent reflexes, severe apnoea, extremely low HR, no respiratory effort, flat EEG)
What HIE stage is a baby if they are having seizures?
Stage 2 moderate or above, no longer considered Stage 1 mild - however, seizures don’t usually begin until >6h of life so it will be too late for cooling
Apgar Scoring System
Appearance (skin colour)
- 0 blue/pale
- 1 blue extremities
- 2 no cyanosis
Pulse rate
- 0 <60bpm
- 1 60-100bpm
- 2 >100bpm
Grimace
- 0 no response
- 1 aggressive stimulation for cry needed
- 2 cries on stimulation
Activity (tone)
- 0 absent/flaccid
- 1 some flexion
- 2 flexes and resists extension
Respiratory effort
- 0 absent
- 1 weak/gasping
- 2 strong cry
Interpretation of Apgar score
7+ = routine care
4-6 = moderate distress, possible intervention of O2 or stimulation needed
<4 = severe distress, immediate CPR, indicative of asphyxia or HIE
Therapeutic Hypothermia (TH)
Neuroprotective treatment for neonates with mod-severe HIE. It reduces brain injury by:
- Slowing metabolic demands
- ↓ excitotoxicity and active processes
- ↓ inflammation
- Therefore inhibits apoptosis
TH Criteria
- Mod-Severe Sarnat score
- Apgar Score <5 at 5 and 10 mins of life
- Within 6h of life
- Must be >35 weeks gestational age
- Must be >1.8kg
Methods of TH
Cooling cap or full body cooling with an oesophageal/rectal thermal probe to monitor temp.
TH Protocol
- Must happen in Latent phase as this is the most amenable to treatment, it reduces the active processes that happen in this phase
- Target temp. 33-34 degrees Celsius
- Total duration: 84h (72h cooling, 12h gradual re-warming by 0.2-0.5 degree/h to 36.5-37 degrees)
Contraindications for TH
- Severe anomalies
- Severe pulmonary HTN
- Severe bleeding issues
- Severe form of HIE - would be futile
- If the neonate is >6h old
