Hypoxic-Ischemic Encephalopathy (HIE)

Physiologic & Intrapartum Criteria (Part A)

• Gestational age >= 36 weeks AND less than 6 hours of absolute postnatal age.
• Evidence of massive acute asphyxial event (abruption, cord prolapse, severe decelerations).
• Umbilical cord gas OR postnatal blood gas (within 1 hour) shows explicit profound acidosis: pH <= 7.00 OR Base Deficit >= 16 mmol/L.
• If pH is 7.01-7.15 (or BD 10-15.9), additional markers are required: 10-minute Apgar <= 5, OR need for prolonged manual PPV/intubation > 10 minutes at birth.

Sarnat Staging & Neurologic Exam Criteria (Part B)

• Must exhibit Moderate to Severe Encephalopathy involving >= 3 out of 6 distinct categories.
• 1. Level of Consciousness: Lethargy, stupor, or coma.
• 2. Spontaneous Activity: Decreased or completely absent.
• 3. Posture: Distal flexion, complete decerebrate, or flaccid.
• 4. Tone: Focal or general hypotonia, or absolute flaccidity.
• 5. Primitive Reflexes: Incomplete/absent suck, or weak/absent Moro.
• 6. Autonomic System: Constricted/deviated pupils, severe bradycardia, or periodic/apneic breathing.
• The presence of clinical/electrographic seizures automatically qualifies the infant regardless of remaining scores.

Therapeutic Hypothermia Execution Protocol

• Initiate active cooling immediately (target esophageal/rectal core temp exactly 33.5°C) strictly before 6 hours of life.
• Maintain precise target range (33.0°C - 34.0°C) for exactly 72.0 continuous hours.
• Rewarming protocol: Extremely slow, incremental rewarming at exactly 0.5°C per hour over a 6-12 hour span (must avoid rebound seizures).
• Pain Management during cooling: Morphine or Fentanyl continuous IV infusion to prevent 'shivering' stress response.
• Rigorous continuous aEEG (Amplitude-integrated EEG) application required through entire cooling and rewarming phases.

Systemic Complications Management

• Cardio: Sinus bradycardia is an EXPECTED physiologic response to cooling (HR 70-100 is acceptable if perfusion is normal); monitor for QT prolongation.
• Renal: Acute Tubular Necrosis (ATN) is extremely common (oliguria). Strictly restrict fluids (commonly ~60 mL/kg/day).
• Hepatic/Heme: Monitor for coagulopathy and DIC (check platelets, PT/INR, PTT, Fibrinogen daily).
• Metabolic: Avoid hyperoxia (target SpO2 90-95%) and precisely target strict normocarbia (PaCO2 40-50). Hypocarbia induces profound cerebral vasoconstriction which compounds ischemia.

Diagnostic & Management Algorithm

• Active Cooling / Therapeutic Hypothermia Protocol: [TIME 0] Verify pH<7.0/BD>16 and Sarnat >=2 -> [TIME <6 Hours] Initiate BlanketROL/Cool Cap -> [ACTION] Target esophageal probe strictly to 33.5C -> [DURATION] Maintain 72.0 hours -> [REWARM] Increase core temp by 0.5C per hour over 6-12 hours until 36.5C

References

1. Jacobs SE, Berg M, Hunt R, et al. Cooling for newborns with hypoxic ischaemic encephalopathy. Cochrane Database Syst Rev.
2. Shankaran S, Laptook AR, Ehrenkranz RA, et al. Whole-body hypothermia for neonates with hypoxic-ischemic encephalopathy. N Engl J Med.