SAPS II (Simplified Acute Physiology Score II)

The SAPS II (Simplified Acute Physiology Score II) is a severity-of-illness scoring system designed for adult patients (aged ≥18 years) in intensive care units (ICUs). Developed in 1993 from a large multicenter study involving 13,152 patients across 137 ICUs in 12 countries, SAPS II predicts hospital mortality risk based on physiological, demographic, and clinical data collected within the first 24 hours of ICU admission. It is widely used for risk stratification, quality benchmarking, and research in adult critical care settings.

Purpose

• Clinical: Quantifies illness severity to guide resource allocation and inform prognosis discussions.
• Quality Benchmarking: Adjusts for patient risk to compare ICU performance across institutions.
• Research: Standardizes risk adjustment in critical care studies.
• Prognostic: Estimates hospital mortality risk for patient cohorts, not individual decisions.

Components of SAPS II Score

The SAPS II score (range: 0–163) is calculated from 17 variables, using the worst values within the first 24 hours of ICU admission:

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1. Physiological Variables (12):

    

   • Heart rate (beats/min)
   • Systolic blood pressure (mmHg)
   • Body temperature (°C)
   • PaO₂/FiO₂ ratio (if ventilated or on CPAP)
   • Urinary output (L/24h)
   • Serum urea or BUN (mmol/L or mg/dL)
   • White blood cell count (×10³/mm³)
   • Serum potassium (mmol/L)
   • Serum sodium (mmol/L)
   • Serum bicarbonate (mmol/L)
   • Bilirubin (mg/dL)
   • Glasgow Coma Scale (GCS)
2. Age: Scored based on age ranges (e.g., <40 years: 0 points; ≥80 years: 18 points).
3. Type of Admission: Scheduled surgical, unscheduled surgical, or medical (e.g., medical: 6 points).
4. Underlying Disease (3):

    

   • AIDS (17 points if present)
   • Metastatic cancer (9 points)
   • Hematologic malignancy (10 points)

Each variable is assigned points based on predefined thresholds. The total score is used in a logistic regression equation to estimate hospital mortality probability.

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Scoring Example

• A 70-year-old patient (12 age points) with septic shock (medical admission: 6 points), no underlying diseases (0 points), and worst values:

   

  • Heart rate 140 beats/min (7 points)
  • Systolic BP 60 mmHg (13 points)
  • GCS 10 (5 points)
  • Other physiological variables contributing 20 points.
• Total SAPS II score = 12 + 6 + 0 + 7 + 13 + 5 + 20 = 63.
• A score of 63 may predict a mortality probability of ~60–70%, depending on the logistic equation.

Clinical Application

1. Risk Stratification: Identifies high-risk patients for intensified monitoring or interventions.
2. Prognostic Guidance: Provides objective data for family counseling, combined with clinical judgment.
3. Quality Improvement: Calculates standardized mortality ratios (SMR = observed/predicted deaths) to assess ICU performance.
4. Research: Facilitates risk-adjusted comparisons in clinical trials or observational studies.

Advantages

• Simplicity: Uses 17 variables, fewer than APACHE II, and is freely available unlike APACHE III.
• Validated: Good discrimination (AUC 0.86–0.88) in large multicenter studies.
• Comprehensive: Incorporates physiology, age, admission type, and comorbidities.
• Standardized: Enables global ICU comparisons due to its broad development dataset.

Limitations

• Adult Focus: Not validated for patients <18 years; use PRISM or PIM3 for pediatric ICUs, SNAP-II/SNAPPE-II for NICUs.
• Time-Sensitive: Uses 24-hour worst values, missing later clinical changes.
• Calibration: May overestimate mortality in modern ICUs due to advances in care since 1993; requires periodic recalibration.
• Cohort-Based: Designed for group risk prediction, not individual prognosis.
• Data Requirements: Needs accurate physiological data (e.g., arterial blood gas for PaO₂), which may be challenging in resource-limited settings.

Implementation

• Data Collection: Use standardized protocols for measurements (e.g., lowest GCS, accurate urinary output). If sedated, estimate GCS before sedation.
• Calculation: Use validated SAPS II scoring tables or online calculators (e.g., ClinCalc.com). Apply the logistic regression formula for mortality probability.
• Interpretation: Combine score with clinical context and diagnosis. Avoid sole reliance on SAPS II for treatment decisions.
• Training: ICU staff need training to ensure consistent data collection and minimize scoring variability.

Comparison with Other Scores

• APACHE II: Similar physiological focus but uses 12 variables and chronic health points; SAPS II includes admission type and specific diseases.
• SAPS III: Updated in 2005 with 20 variables, better calibration, but less widely used.
• SOFA: Tracks organ dysfunction over time, less focused on admission severity.
• MPM II: Uses admission data only, simpler but less comprehensive.

SAPS II remains popular for its balance of simplicity and predictive power in adult ICUs.

Relevance to Other Settings

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

Conclusion

The SAPS II score is a robust, widely used tool for assessing illness severity and predicting hospital mortality in adult ICU patients. Its 17-variable framework, incorporating physiological, demographic, and clinical factors, supports risk stratification, quality benchmarking, and research. Medical professionals should integrate SAPS II with clinical judgment, ensuring accurate data collection and context-specific interpretation. While calibration may require updates due to evolving ICU practices, SAPS II remains a cornerstone of adult critical care assessment.