What is the SAPS II Score?
The SAPS II (Simplified Acute Physiology Score II) is a 17-variable severity-of-illness scoring system that predicts hospital mortality risk in ICU patients by incorporating 12 physiologic measurements, age, admission type, and three underlying disease conditions. 1
Core Components of SAPS II
The SAPS II includes the following variables collected within the first 24 hours of ICU admission:
Physiologic Variables (12 parameters):
- Heart rate
- Systolic blood pressure
- Temperature
- PaO2/FiO2 ratio (if ventilated) or PaO2 alone (if not ventilated)
- Urine output
- Serum urea nitrogen
- White blood cell count
- Serum potassium
- Serum sodium
- Serum bicarbonate
- Bilirubin
- Glasgow Coma Scale score 1
Demographic and Clinical Variables:
- Age (continuous variable)
- Type of admission: scheduled surgical, unscheduled surgical, or medical 1
Underlying Disease Variables:
- Acquired immunodeficiency syndrome (AIDS)
- Metastatic cancer
- Hematologic malignancy 1
How SAPS II is Calculated
Each variable is assigned points based on the degree of abnormality, with the total score ranging from 0 to 163 points. 1 The raw SAPS II score is then converted to a predicted probability of hospital mortality using a logistic regression equation developed from the original validation cohort. 1
Predictive Performance
SAPS II demonstrates strong discriminative ability for mortality prediction, with an area under the receiver operating characteristic curve (AUROC) of 0.86 in the original validation sample 1 and 0.80 in more contemporary cohorts. 2 The score performs well for both in-hospital mortality (AUROC 0.80) and 90-day mortality (AUROC 0.79), with no significant difference between these timeframes. 2
SAPS II outperforms the initial SOFA score for mortality prediction (AUROC 0.80 vs. 0.73, P<0.001). 2
Clinical Applications
Risk Stratification: SAPS II accurately classifies patients into groups of increasing probability of death, regardless of primary diagnosis. 1, 3
Quality Assessment: The score enables comparison of ICU performance across different units and time periods by comparing observed-to-predicted mortality ratios. 4, 5
Research Standardization: SAPS II provides a validated method for adjusting for baseline severity when evaluating mortality, morbidity, and quality of life outcomes in critically ill patients. 6
Important Caveats
Temporal Drift: The predictive performance of SAPS II has decreased over time since its 1993 development, with contemporary AUROCs (0.80) lower than the original validation (0.86, P=0.001). 2 This reflects changes in ICU care practices and patient populations over three decades.
Calibration Issues: Some studies report under-prediction of actual mortality, with observed-to-predicted ratios as high as 1.6 in certain ICU populations. 4 This necessitates local recalibration when using SAPS II for institutional benchmarking.
Exclusions: SAPS II was not developed for burn patients, coronary care patients, or cardiac surgery patients, and should not be applied to these populations. 1
Data Collection Burden: Unlike simpler scoring systems, SAPS II requires collection of 17 variables, making it more time-consuming than alternatives like the original SAPS (14 variables). 3