11.2 HIE, PVL, Stroke, and Therapeutic Hypothermia
Key Takeaways
- Hypoxic-ischemic encephalopathy is a clinical picture after perinatal asphyxia; Sarnat-style staging (mild, moderate, severe) organizes tone, consciousness, reflexes, and seizures.
- Typical cooling practice — not an AACN-published number set — enrolls infants at about 36 weeks or more, starts by 6 hours of age, and treats moderate-severe encephalopathy for 72 hours at a core temperature near 33.5°C, then rewarms slowly.
- Secondary energy failure begins hours after the insult, which is why the decision window is early and why glucose, carbon dioxide, blood pressure, seizures, and fever still matter on and off the blanket.
- PVL is preterm white-matter watershed injury, often after hypoperfusion, hypocarbia, or inflammation; cysts can appear weeks later, so an early ultrasound can be falsely reassuring.
- Perinatal arterial ischemic stroke is typically a term infant with focal seizures, often left middle-cerebral-artery territory; do not cool isolated stroke unless the infant also meets encephalopathy criteria.
11.2 HIE, PVL, Stroke, and Therapeutic Hypothermia
Quick Answer: Hypoxic-ischemic encephalopathy (HIE) is a clinical syndrome after perinatal asphyxia. Stage it conceptually with a Sarnat-style exam (mild hyperalert, moderate lethargic with seizures, severe stuporous and flaccid). Therapeutic hypothermia is the disease-modifying therapy for moderate-severe HIE in typical practice: about ≥36 weeks, start within 6 hours, 72 hours at a core temperature near 33.5°C, then slow rewarming. AACN does not publish those trial numbers in the handbook; treat them as common clinical protocol, not as official exam-owner constants. PVL is preterm white-matter injury. Perinatal arterial ischemic stroke is usually a term, focal-seizure presentation. Chapter 16 lists cooling among advanced therapies; the protocol lives here.
HIE: Two Patterns, One Secondary-Injury Clock
HIE follows interrupted placental gas exchange, a collapsed umbilical circuit, or failed transition. Two injury patterns show up on later magnetic resonance imaging and help you think about the delivery story:
- Acute profound ischemia (terminal bradycardia, ruptured uterus, cord prolapse) preferentially injures deep gray nuclei — basal ganglia and thalamus — and the perirolandic cortex. Infants may look severely encephalopathic and have a high seizure burden.
- Partial prolonged ischemia (repeated late decelerations, sentinel events stretched over time) prefers watershed cortex and subcortical white matter.
Many infants are mixed. The nursing job in the first hours is not to name the MRI pattern; it is to stop secondary energy failure. After resuscitation, neurons may partially recover, then fail again over the next 6–24 hours as excitatory amino acids, oxidative stress, and mitochondrial injury accumulate. That biology is why cooling trials used a 6-hour start window. After that window, standard whole-body cooling is no longer the evidence-based default; late cooling belongs to research protocols, not to improvisation at 18 hours of age.
HIE is a multi-organ disease. Expect myocardial stunning, pulmonary hypertension, acute kidney injury, hepatic enzyme leaks, coagulopathy, and bowel ischemia. Those organs are taught in other chapters. Neurologic care still owns airway protection, glucose, temperature, seizure recognition, and the cooling decision.
Sarnat-Style Staging — Conceptual, Not a Handbook Table
AACN Certification Corporation's Neonatal CCRN Test Plan names ischemic insult; it does not print a Sarnat table. Use the clinical picture anyway, because eligibility for cooling is an encephalopathy exam, not a single cord pH.
| Conceptual stage | Consciousness | Tone and reflexes | Seizures | Typical course |
|---|---|---|---|---|
| Mild (stage 1) | Hyperalert, irritable | Normal or increased tone; strong suck | Usually none | Often <24 hours; supportive care, not standard cooling |
| Moderate (stage 2) | Lethargic | Hypotonia, especially distal; weak suck and Moro | Common | Cooling candidate when other criteria are met |
| Severe (stage 3) | Stupor or coma | Flaccid; primitive reflexes poor or absent | Variable; EEG often suppressed | Cooling candidate; prognosis guarded |
Re-examine. A baby who looks mild at 20 minutes and moderate at 90 minutes has declared. Document pupillary response, fontanelle, posture, suck, Moro, gag, and whether breathing is sufficient. Amplitude-integrated EEG (aEEG) supports the exam: a continuous normal voltage pattern is encouraging; burst suppression or a flat trace is not. Clinical seizures are easy to miss in encephalopathic neonates, which is why many cooling programs run continuous aEEG.
Typical Therapeutic Hypothermia Criteria (Clinical Practice)
State these as trial-derived unit practice, not as AACN-published cutoffs. Major whole-body and selective-head cooling trials enrolled infants who looked like this:
- Gestational age typically 36 weeks or more (some NICUs consider selected 35-week infants under a written protocol; do not treat a 26-week infant with a stormy transition as a cooling candidate).
- Postnatal age under 6 hours at start.
- Evidence of a hypoxic-ischemic event: often a cord or early postnatal pH around 7.0 or below or a base deficit around 16 mmol/L or more, or a combination of a less extreme blood gas plus a sentinel event plus a 10-minute Apgar around 5 or less or ongoing ventilation at 10 minutes. Units print their exact numbers. Memorize the idea: biochemical asphyxia plus a delivery story, not a single Apgar.
- Moderate or severe encephalopathy on exam, or seizures, using a Sarnat-style or Thompson-style score.
Common exclusions in written protocols include anomalies incompatible with life, uncorrectable surgical conditions, refractory hemorrhage, and families who decline after counseling. Mild isolated encephalopathy was not the original trial population.
The Protocol: 72 Hours, Then Slow Rewarming
Most U.S. NICUs now use servo-controlled whole-body cooling. Place a rectal or esophageal temperature probe (esophageal is often preferred as a core proxy for whole-body systems). Target a core temperature near 33.5°C (typical range 33–34°C). Selective head cooling with a slightly higher rectal target exists historically; if your unit still uses it, follow that device's protocol rather than mixing numbers.
Cool for 72 hours. Expected findings during hypothermia include sinus bradycardia (heart rates in the 70s–100s can be appropriate), a longer QT interval, decreased drug clearance, slower gut motility, and skin that is easy to injure under blankets. Check skin on a schedule. Subcutaneous fat necrosis can appear later. Coagulopathy and thrombocytopenia worsen in the cold; send serial counts and treat bleeding, but do not abandon indicated cooling for an isolated mild platelet drop without a protocol conversation.
Metabolism and pharmacology change. Morphine, midazolam, phenobarbital, and many other infusions accumulate. Glucose can fall or rise; both hypoglycemia and marked hyperglycemia worsen brain injury. Electrolytes shift: hypokalemia is common while cold; hyperkalemia and vasodilation can appear during rewarming. Pulmonary hypertension may intensify — have nitric oxide and a PPHN plan ready rather than assuming cooling is “just a temperature order.”
Rewarm slowly, typically about 0.5°C per hour (some protocols use 0.2–0.5°C per hour over 6–12 hours). Fast rewarming is associated with seizures, hypotension, and rebound hyperthermia. After normothermia, avoid fever. Hyperthermia after HIE is a second hit whether or not the infant was cooled.
Sedation during cooling treats shivering, irritability, and ventilator dyssynchrony. It is not a substitute for seizure treatment. Paralysis without analgesia is never acceptable (section 11.3). Keep parents at the bedside: the blanket looks alarming; daily plain-language updates on exam, aEEG, and organ recovery beat a single MRI speech on day 5.
MRI is often obtained after rewarming (commonly around day 4–7, sometimes later for practice logistics). Deep-gray injury, watershed injury, and mixed patterns inform prognosis but do not replace serial exams and family values. Early intervention referral is part of discharge planning, not an afterthought.
Worked Cooling Scenario
A 39-week infant is born after uterine rupture. Cord pH is 6.90, base deficit 18 mmol/L, and the 10-minute Apgar is 4 with ongoing ventilation. At 90 minutes the infant is lethargic, hypotonic, with a weak suck and clinical seizures. This infant meets typical cooling eligibility: near-term, within 6 hours, clear asphyxia biochemistry, moderate-severe encephalopathy. Start servo whole-body cooling, place aEEG, treat glucose and blood pressure, load an anticonvulsant per unit seizure protocol (chapter 10), and counsel that cooling lasts 72 hours. Do not wait for MRI to decide. Do not cool a vigorous, hyperalert infant with a single low pH and a normal exam.
PVL in Preterm Infants
Periventricular leukomalacia is ischemic and inflammatory injury to the white-matter watershed supplied by long and short penetrating arteries. The population is the 24- to 32-week infant, not the cooled term infant. Risk factors include hypotension, hypocarbia, sepsis and chorioamnionitis (cytokine injury), and intrauterine growth restriction. Cystic PVL appears as macrocysts in the white matter, often 2–4 weeks after the insult — another reason a day-of-life-2 ultrasound can be falsely quiet. Diffuse noncystic white-matter injury is even more common and is better seen on MRI.
Later motor signature is often spastic diplegia, with legs more involved than arms, plus visual and cognitive risk. Prevention overlaps the IVH bundle: stable carbon dioxide, adequate perfusion, infection control, and gentle ventilation. PVHI from section 11.1 is a different lesion: asymmetric hemorrhagic venous infarction tied to large IVH, not symmetric watershed cysts.
Perinatal Arterial Ischemic Stroke
Perinatal arterial ischemic stroke (PAIS) typically presents in a term infant with focal seizures in the first hours to days of life. The left middle cerebral artery is the most common territory. Tone may be subtly asymmetric; frank hemiparesis is easy to miss in a newborn. Estimated incidence is on the order of 1 in 2500–4000 live births in many series — uncommon, but common enough that “focal seizures, term baby, metabolic labs pending” should trigger MRI with diffusion-weighted imaging, not only a glucose stick.
Risk associations include congenital heart disease, meningitis, thrombophilia, chorioamnionitis, and a placental clot that embolizes through a patent foramen ovale — none of which you will confirm at the first seizure. Acute care is supportive: airway, glucose, treat seizures, evaluate infection and heart disease. Routine anticoagulation is not first-line for isolated arterial stroke. Cerebral sinovenous thrombosis is a different disease and is more often considered for anticoagulation when hemorrhage is not prohibitive. Do not start whole-body hypothermia for isolated PAIS unless the infant independently meets HIE cooling criteria.
Neuroprotection When You Are Not Cooling
Every ischemic insult, cooled or not, still needs the secondary-injury list: normoxemia, adequate blood pressure, mid-range PaCO2, treated seizures, treated hypoglycemia, and no fever. Maternal magnesium given before preterm birth is an obstetric white-matter strategy; it does not replace neonatal hemodynamics. Erythropoietin and other add-on neuroprotectants remain research or protocol-specific — do not invent them as standard CCRN answers.
A 38-week infant meets typical HIE cooling criteria at 3 hours of age. The usual whole-body protocol is:
Which infant is the usual candidate for a standard neonatal cooling protocol?
A 27-week infant has a relatively quiet early ultrasound. At 3 weeks, bilateral periventricular cysts appear. The mechanism that best fits is:
A 40-week infant is alert between events but has recurrent right-arm clonic seizures at 30 hours of life. Glucose is normal. The most likely ischemic diagnosis to pursue on MRI is: