SNAP-II and SNAPPE-II Scores

The SNAP-II (Score for Neonatal Acute Physiology II) and SNAPPE-II (Score for Neonatal Acute Physiology with Perinatal Extension II) are severity-of-illness scoring systems designed for neonates in neonatal intensive care units (NICUs). Developed in 2001 as simplified updates to the original SNAP scores, they quantify illness severity and predict mortality risk in newborns, particularly preterm or critically ill infants. SNAP-II focuses on physiological parameters, while SNAPPE-II extends SNAP-II by incorporating perinatal factors. These scores are widely used for risk adjustment, outcome prediction, and quality assessment in NICUs.

Purpose

• Clinical: Assesses neonatal illness severity to guide resource allocation and prognosis discussions.
• Quality Benchmarking: Adjusts for patient risk to compare NICU performance across institutions.
• Research: Standardizes risk adjustment in neonatal studies.
• Prognostic: Estimates mortality risk before hospital discharge for cohorts, not individual decisions.

Components of SNAP-II

SNAP-II uses six physiological variables collected within the first 12 hours of NICU admission, focusing on the worst values observed:

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1. Mean Blood Pressure (mmHg): Reflects cardiovascular stability.
2. Lowest Temperature (°C): Indicates thermoregulation issues.
3. PO₂/FiO₂ Ratio: Measures oxygenation efficiency.
4. Lowest Serum pH: Reflects acid-base balance.
5. Multiple Seizures: Indicates neurological instability (yes/no).
6. Urine Output (mL/kg/h): Assesses renal function and perfusion.

Each variable is scored based on predefined thresholds (e.g., 0, 5, 10, or 20 points), with higher points for greater deviation from normal. The total SNAP-II score (0–90) correlates with illness severity and mortality risk.

Components of SNAPPE-II

SNAPPE-II extends SNAP-II by adding three perinatal factors to improve mortality prediction:

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1. Birth Weight (g): Lower weight increases risk.
2. Small for Gestational Age (SGA): Defined as <3rd percentile for gestational age.
3. Apgar Score at 5 Minutes: Low scores indicate perinatal distress.

The SNAPPE-II score (0–126) is the sum of the SNAP-II score plus points from these perinatal factors. It is more predictive of mortality than SNAP-II alone, especially for preterm or low-birth-weight infants.

Scoring Example

• SNAP-II: A neonate with:

   

  • Mean BP 30 mmHg (5 points)
  • Lowest temperature 35.0°C (5 points)
  • PO₂/FiO₂ ratio 1.5 (10 points)
  • Serum pH 7.15 (5 points)
  • No seizures (0 points)
  • Urine output 0.5 mL/kg/h (10 points)
  • Total SNAP-II score = 5 + 5 + 10 + 5 + 0 + 10 = 35

• SNAPPE-II: Same neonate with:

   

  • Birth weight 1000 g (10 points)
  • SGA (5 points)
  • 5-minute Apgar score 4 (10 points)
  • Total SNAPPE-II score = 35 (SNAP-II) + 10 + 5 + 10 = 60
• A SNAPPE-II score of 60 may predict a mortality risk of ~30–50%, depending on calibration.

Clinical Application

1. Risk Stratification: Identifies high-risk neonates for intensified monitoring or interventions.
2. Prognostic Guidance: Provides objective data for family counseling, combined with clinical judgment.
3. Quality Improvement: Adjusts mortality rates for illness severity, enabling fair NICU performance comparisons.
4. Research: Standardizes risk in studies of neonatal interventions or outcomes.

Advantages

• Simplicity: SNAP-II uses only six variables, and SNAPPE-II adds three, making them easier to calculate than earlier scores (e.g., original SNAP).
• Early Assessment: Data is collected within 12 hours, enabling prompt risk evaluation.
• Validated: Extensively studied across diverse neonatal populations, including preterm and term infants.
• Broad Applicability: Unlike CRIB II (focused on preterm infants <32 weeks), SNAP-II/SNAPPE-II apply to all NICU admissions.
• Improved Prediction: SNAPPE-II enhances mortality prediction by including perinatal factors.

Limitations

• Time-Sensitive: Relies on 12-hour worst values, missing later clinical changes.
• Calibration: Mortality predictions may vary by region, NICU practices, or population, requiring recalibration.
• Cohort Focus: Designed for group risk prediction, not individual prognosis.
• Data Requirements: Requires precise measurements (e.g., arterial blood gas for pH), which may be challenging in resource-limited settings.
• Not Diagnosis-Specific: Does not account for congenital anomalies or specific conditions, unlike some newer scores.

Implementation

• Data Collection: Use standardized protocols for accurate measurement (e.g., arterial blood gas for pH, calibrated temperature probes). Ensure consistent Apgar scoring for SNAPPE-II.
• Calculation: Use validated SNAP-II/SNAPPE-II scoring tables or software. Online calculators are available.
• Interpretation: Combine scores with clinical context and diagnosis. Avoid sole reliance on scores for treatment decisions.
• Training: NICU staff need training to ensure consistent data collection and score application.

Comparison with Other Scores

• CRIB II: Focuses on preterm infants (<32 weeks or ≤1500 g), using gestational age, birth weight, and early physiological data. Simpler but less applicable to term infants.
• PRISM III: For pediatric ICUs, not suitable for neonates due to different physiological norms.
• APACHE II: For adult ICUs, inappropriate for neonates.
• NTISS: Measures therapeutic intensity, not mortality risk, complementing SNAP-II/SNAPPE-II.

SNAP-II/SNAPPE-II are preferred in NICUs for their neonatal focus and balance of simplicity and predictive power.

Relevance to Other Settings

• Pediatric ICUs: Not suitable for older children; use PRISM III or PIM3.
• Adult ICUs: Inappropriate; use APACHE II or SAPS II.
• Mixed ICUs: Apply SNAP-II/SNAPPE-II for neonatal patients only, with separate tools for pediatric or adult cases.

Conclusion

The SNAP-II and SNAPPE-II scores are robust, neonatal-specific tools for assessing illness severity and predicting mortality in NICU patients. SNAP-II’s six physiological variables offer a simple yet effective measure, while SNAPPE-II’s perinatal factors enhance prognostic accuracy. Their ease of use, early applicability, and validation make them invaluable for risk stratification, quality benchmarking, and research. Medical professionals should integrate these scores with clinical judgment, ensuring accurate data collection and context-specific interpretation. They are particularly suited for diverse NICU populations, complementing other neonatal scores like CRIB II.