In a term newborn (≥36 weeks) with hypoxic‑ischemic encephalopathy meeting criteria for therapeutic hypothermia (severe acidosis, low 10‑minute Apgar, or prolonged resuscitation), how do the Sarnat staging and Thompson neurological score differ in timing, components, and clinical utility, and which should be used first to determine eligibility for cooling?

Sarnat vs Thompson Score: Key Differences and Clinical Application

Use the Thompson score at 3-5 hours of life for initial triage and cooling eligibility decisions, as it demonstrates superior sensitivity (100%) for predicting moderate-to-severe HIE and abnormal neurological outcomes compared to waiting for formal Sarnat staging. 1

Timing of Assessment

Thompson Score:

• Designed for early assessment at 3-5 hours of life 1
• Provides rapid triage capability within the critical 6-hour therapeutic window 1
• Can be repeated serially to track neurological evolution 1

Sarnat Staging (Modified Sarnat Examination):

• Traditionally performed after initial stabilization 2
• Used in major hypothermia trials to define moderate-to-severe HIE requiring treatment 2
• Should be performed daily during the cooling period to track improvement 3
• Most frequently used tool in randomized controlled trials for hypothermia eligibility 2

Components and Scoring Systems

Thompson Score:

• Quantitative scoring system with numerical values 1
• Evaluates multiple neurological parameters with weighted scores 1
• A score ≥7 at 3-5 hours predicts abnormal 6-hour aEEG with 100% sensitivity and 67% specificity 1
• Predicts moderate-to-severe HIE within 72 hours with 90% sensitivity and 92% specificity 1

Modified Sarnat Examination:

• Categorical assessment across 6 domains: level of consciousness, spontaneous activity, posture, tone, primitive reflexes (Moro, grasp, suck), and autonomic system 2
• Each category scored as normal, mild, moderate, or severe 2
• Requires ≥3 of 6 categories in moderate or severe range to qualify for hypothermia (as used in randomized trials) 2
• At 3-5 hours, moderate-severe grading predicts abnormal 6-hour aEEG with 97% sensitivity and 71% specificity 1

Clinical Utility and Performance

Thompson Score Advantages:

• Superior early predictive value: 100% sensitivity for identifying infants who will develop abnormal 6-hour aEEG 1
• Better sensitivity than 6-hour aEEG alone for predicting moderate-severe HIE within 72 hours (90% vs 75%, p=0.0156) 1
• Provides objective numerical threshold for decision-making 1
• Useful for rapid triage when transfer to cooling center is needed 1

Sarnat Staging Advantages:

• Standard assessment used in all major therapeutic hypothermia trials 2
• Well-validated for prognostication when performed serially 3
• Improvement in Sarnat stage from admission to day 4 strongly predicts favorable outcome (OR 0.118 for unfavorable outcome if improvement occurs) 3
• More widely recognized internationally for defining HIE severity 4

Recommended Clinical Algorithm

Step 1: Initial Assessment (Birth to 3 hours)

• Identify infants meeting biochemical/historical criteria: pH ≤7.0, base deficit ≥12 mmol/L, Apgar ≤5 at 10 minutes, or need for resuscitation at 10 minutes 5, 2
• Begin continuous monitoring and stabilization 5

Step 2: Early Neurological Evaluation (3-5 hours of life)

• Perform Thompson score first 1
• If Thompson score ≥7: immediately initiate cooling protocol or arrange urgent transfer 1
• Simultaneously perform modified Sarnat examination 2
• If ≥3 of 6 Sarnat categories are moderate or severe: confirms cooling eligibility 2

Step 3: Confirmatory Assessment (6 hours)

• Obtain amplitude-integrated EEG if available 1, 2
• Do not delay cooling initiation waiting for aEEG if clinical criteria met 6, 7
• Remember: 52% of infants without hypotonia at 3-5 hours still had abnormal 6-hour aEEG 1

Step 4: Serial Monitoring (Days 1-4)

• Repeat Sarnat staging daily 3
• Improvement by day 4 is highly predictive of favorable 18-24 month outcome 3
• Maintain strict temperature control at 33-34°C for 72 hours 4, 6, 7

Critical Pitfalls to Avoid

Common Assessment Errors:

• Do not rely solely on presence/absence of hypotonia: 52% without hypotonia still had abnormal outcomes 1
• Do not wait for decreased level of consciousness: 41% without altered consciousness at 3-5 hours had abnormal 6-hour aEEG 1
• All infants with suspected HIE have at least one abnormal primitive reflex - this alone is insufficient for diagnosis 1

Timing Errors:

• Never delay cooling beyond 6 hours waiting for "better" clinical assessment 6, 7, 5
• Efficacy of hypothermia decreases significantly after 6-hour window 6, 5

Facility Requirements:

• Only initiate cooling in facilities with multidisciplinary capabilities: IV therapy, mechanical ventilation, pulse oximetry, anticonvulsants, and pathology testing 4, 6, 7
• If these resources unavailable, arrange immediate transfer while maintaining passive cooling with target temperature 33.5°C ± 0.5°C 2

Prognostic Value

Both scoring systems predict outcomes, but with different strengths:

• Thompson score at 3-5 hours: 90% sensitivity for moderate-severe HIE within 72 hours 1
• Sarnat improvement by day 4: OR 0.118 for unfavorable outcome at 18-24 months if improvement occurs 3
• Therapeutic hypothermia reduces death or major disability by 22-33% when properly selected patients are treated 6, 7
• Number needed to treat: 5-7 infants to prevent one death or severe disability 6, 7, 5