The standard of care for cooling neonates suffering from hypoxic-ischemic encephalopathy (HIE) is therapeutic hypothermia, also known as neonatal cooling or brain cooling. This treatment has been shown to significantly improve survival rates and reduce the risk of long-term neurodevelopmental disabilities, such as cerebral palsy and cognitive impairment, in infants with moderate to severe HIE.
Here’s a breakdown of the key aspects of this standard of care:
Who is eligible?
Gestational age: Typically, infants born at ≥ 36 weeks of gestation. Some guidelines consider infants ≥ 35 weeks if they meet other criteria. Cooling is generally not recommended for infants younger than 35 weeks.
Age at initiation: Cooling should ideally be initiated within the first 6 hours of birth. While some research suggests potential benefits up to 12-24 hours, the strongest evidence supports treatment within the first 6 hours.
Evidence of moderate to severe HIE: This is determined by a combination of factors, including:
- Apgar score of 5 or less at 10 minutes.
- Need for prolonged resuscitation at birth (≥ 10 minutes of positive-pressure ventilation).
- Acidosis on umbilical cord or early blood gas (pH < 7.0 or base excess ≤ -12 to -16 mmol/L within the first 60 minutes).
- Clinical signs of moderate to severe encephalopathy (assessed using standardized scoring systems like the Sarnat score, including decreased level of consciousness, abnormal tone, abnormal reflexes, and seizures).
How is it performed?
Therapeutic hypothermia involves lowering the baby’s core body temperature to a target range of 33.5°C to 34.5°C (92.3°F to 94.1°F) for a duration of 72 hours. This can be achieved through two main methods:
- Whole-body cooling: Using a special cooling blanket with circulating water to lower the entire body temperature. Core temperature is continuously monitored using a rectal or esophageal probe.
- Selective head cooling: Using a cooling cap that circulates cold water specifically around the baby’s head, while the body may be kept at a near-normal temperature.
Care during cooling:
During the 72-hour cooling period, the neonate receives intensive care in the Neonatal Intensive Care Unit (NICU) with close monitoring of:
- Vital signs: Heart rate, blood pressure, respiration, oxygen saturation, and continuous core temperature.
- Neurological status: Frequent neurological assessments, including level of consciousness, tone, reflexes, and monitoring for seizures (often with continuous EEG).
- Cardiovascular support: Management of potential bradycardia (slow heart rate) and hypotension (low blood pressure).
- Respiratory support: Often requires mechanical ventilation to ensure adequate oxygenation and ventilation.
- Fluid and electrolyte balance: Careful management to prevent complications like dehydration or electrolyte disturbances.
- Glucose levels: Monitoring and maintaining stable blood glucose.
- Sedation and pain management: Medications like morphine may be used to prevent shivering and ensure comfort.
Rewarming:
After 72 hours of cooling, the baby is gradually rewarmed at a slow rate (typically 0.2°C to 0.5°C per hour) until a normal body temperature (36.5°C to 37°C or 97.7°F to 98.6°F) is reached. This rewarming phase usually takes at least 4 hours, and often 6-12 hours, to minimize the risk of reperfusion injury and other complications. Continuous monitoring is crucial during rewarming as well, as seizures can be more common during this phase.
Supportive care:
In addition to cooling, neonates with HIE often require significant supportive care, including:
- Respiratory support (oxygen, ventilation).
- Management of seizures with anticonvulsant medications.
- Cardiovascular support (fluids, medications to support blood pressure).
- Nutritional support (often initially through intravenous fluids, with cautious introduction of enteral feeds after rewarming).
- Monitoring and management of other organ system function.
Exclusions:
There are certain conditions where therapeutic hypothermia may not be recommended, including:
- Moribund infants with little hope for meaningful recovery.
- Infants with major congenital anomalies that would significantly impact their long-term prognosis.
- Severe coagulopathy or active bleeding.
- Severe intrauterine growth restriction (in some guidelines).
Follow-up:
Infants who receive therapeutic hypothermia require long-term neurodevelopmental follow-up to monitor their progress and identify any potential disabilities early.
It’s important to note that while therapeutic hypothermia is the standard of care for moderate to severe HIE, research is ongoing to determine its role in mild cases. Current studies are investigating the potential benefits and risks of cooling for infants with milder forms of this condition.