Well, folks! Here it is! The most requested and HIGHLY anticipated post so far. Not gonna lie, this one was a doozy for me to write. The following content is extremely heavy and dense, not to mention undeniably long. You have been warned...
Neonatal Hypoxic Ischemic Encephalopathy (HIE) is a major cause of death and neurodevelopmental disability in term infants around the world. It is a type of serious brain damage that may present shortly after birth. It is characterized by symptoms of central nervous system dysfunction, such as decreased level of consciousness, altered spontaneous activity, or abnormal tone, posture, or reflexes.
Treatment involves purposefully, safely, and carefully, cooling the body temperature. This slows down the basic metabolic functioning of the body and potentially decreases injury to the brain caused by the lack of oxygen and the lack of blood flow. Body cooling is done by placing the infant on a cooling mattress with no external heat source. Esophageal or rectal temperature monitoring ensures consistent, safe temperatures for the infant.
Placement of Esophageal Probe
In my NICU, we exclusively use esophageal probes. In order to insert one, here are the steps:
Measure from the tip of the nose to the tragus of the ear, then to the xiphoid process.
Subtract 2 centimeters from this final length. Mark the probe at the determined length with a piece of tape. Nasal placement is preferred, with the goal being the lower third of the esophagus (approximately 2 centimeters above the diaphragm).
Lubricate the tip of the probe and carefully insert to your desired length. Secure the probe to the infant’s cheek.
Confirming placement with an x-ray is MANDATORY!
Therapeutic Hypothermia
This is defined as whole body cooling to 33.5-34.5°C (92.3-94.1°F) for 72 hours. When the core (esophageal or rectal) body temperature drops below 36°C, oral temperature below 35.5°C, or axillary temperature 34.9°C, this is considered hypothermia.
Adverse effects of hypothermia to monitor for include the following:
Cooled babies have depressed metabolisms, meaning they generate less heat. If the baby has never been warmed, he can be easily overcooled.
It is important to maintain adequate sedation in order to prevent shivering or patient discomfort.
In addition, cooling causes peripheral vasoconstriction, therefore vascular access should be established prior to the initiation of therapy. It is preferable to use umbilical catheters rather than peripheral access.
The purpose of therapeutic hypothermia is to safely and carefully lower the infant’s body temperature. By whole body cooling, the basal metabolic processes slow down, thereby decreasing the severity and extent of brain injury.
Consider this analogy…
Cooling the body/brain is like putting out a fire. It CANNOT reverse and/or fix any damage that has already been done; however, it CAN prevent and stop any future damage from occurring.
NOT ALL BABIES QUALIFY FOR THERAPEUTIC HYPOTHERMIA
To be considered for cooling therapy, eligibility criteria involves meeting all three of the following requirements:
The infant must be greater than or equal to 36 weeks gestation AND less than 6 hours old.
Research shows that when therapeutic hypothermia is initiated within 6 hours of birth, the incidence of death & severity of brain damage is significantly reduced.
Two or more of the following must be met:
Acute perinatal event (i.e. abruptio placenta, cord prolapse, severe FHR abnormalities such as variable or late decels)
Low APGAR scores <5 at 10 minutes of life
Prolonged resuscitation at birth (e.g. chest compressions and or intubation or ventilation at 10 minutes)
Severe acidosis (pH <7.00 from cord blood or patient blood gas within 1 hour postnatally)
Abnormal base excess (-12 from cord blood or blood gas within 1 hour postnatally)
Neurological Examination demonstrates signs of moderate-to-severe encephalopathy.
Moderate Encephalopathy
Level of Consciousness: Lethargic
Spontaneous Activity: Decreased activity
Posture: Distal flexion, full extension
Tone: Hypotonic (focal, general)
Primitive Reflexes: Weak suck & incomplete moro reflex
Autonomic System: Bradycardia, periodic breathing & constricted pupils
Clinical Seizures: Present
Severe Encephalopathy
Level of Consciousness: Stupor/Coma
Spontaneous Activity: No activity
Posture: Decerebrate
Tone: Flaccid
Primitive Reflexes: Absent suck and moro reflex
Autonomic System: Variable HR, Apneas, deviated/dilated or non-reactive to light
Clinical Seizures: Present
Exclusion Criteria for Cooling:
<36 weeks gestation
IUGR (<1.8 kg)
Inability to initiate cooling by 6 hours of life
Severe PPHN (unresponsive to iNO)
Severe hemodynamic compromise/perfusion sensitive states (i.e. Sepsis)
Coagulopathy with active bleeding
History of thrombus
ECMO patient
Severe congenital anomalies/syndromes/known metabolic disorders
In order to safely care for these patients, the RN must have completed a specific training course. It is not within the scope of practice for every NICU RN, as this is considered a 1:1 high acuity patient assignment that requires an advanced skilled nurse.
The infant should be dressed in a diaper only, no hat or other articles of clothing. It is important to monitor and document vital signs every 15 minutes until the patient reaches the goal core temperature of 33.5°C. Afterward, full vital signs should be documented every hour for the duration of the 72 hour hypothermia therapy.
After 72 hours of cooling, the infant is slowly re-warmed and stabilized over 6 hours.
Note: 72 hours of cooling BEGINS at the time the infant reaches the goal core temperature of 33.5°C. This may occur either during transport or in the NICU.
Guidelines for Medical Management
Maintain the infant NPO and start IV fluids for hydration/nutrition.
Collect recommended labs as needed
Manage the acidosis (base excess >-10) via NS, THAM, or sodium bicarb
Treat hypovolemia with fluid replacement boluses and/or transfusions as needed
Provide respiratory support
Expect bradycardia (<100 is normal during this process)
Support BP with fluids or vasopressors if indicated
Start antibiotics for rule out sepsis
Rewarming Procedure
Upon completion of the 72-hour cooling period, the infant will be re-warmed gradually, increasing the core body temperature at a rate of 0.5°C per hour over 6 hours. It is important to avoid rapid rewarming and to maintain a slow, gradual rate. When the esophageal temperature reaches 36.5°C, the nurse will turn off the cooling machine & remove the esophageal probe. The infant will be managed on a warming table with a skin temperature set to 36.5°C.
Note: Rewarming too quickly can cause clinical decompensation. Signs include tachycardia, cardiac arrhythmia, hypotension, or hypoxemia. If these are observed, slowing down the process may be necessary! The phrase “It’s a marathon, not a sprint”—albeit overused, is EXTREMELY relevant in this circumstance.