SAPS II — Simplified Acute Physiology Score II for ICU Mortality Prediction
The Simplified Acute Physiology Score (SAPS II) is a widely validated ICU severity of illness scoring system for predicting hospital mortality, derived from a large European/North American database of 13,152 patients.
About
SAPS II (Simplified Acute Physiology Score II) was developed by Le Gall et al. in 1993 from a multicenter database of 13,152 ICU patients across 12 countries in Europe and North America. It is the second-generation Simplified Acute Physiology Score, replacing the original SAPS with improved accuracy and broader applicability. The score uses the worst values of 12 physiologic variables (age, heart rate, systolic BP, temperature, PaO2/FiO2 ratio for ventilated patients, urine output, serum urea/BUN, WBC count, potassium, sodium, bicarbonate, bilirubin), plus 3 disease-related variables (chronic diseases, admit type, Glasgow Coma Scale). Each variable is assigned weighted points based on logistic regression coefficients. The total score ranges from 0 to 163. Predicted hospital mortality is calculated using the formula: Logit = -7.7631 + 0.0737 × SAPS II score, and Probability = e^logit / (1 + e^logit). The score demonstrates excellent discrimination (c-statistic 0.86-0.88) and calibration across diverse ICU populations. SAPS II is recommended for benchmarking, risk stratification, and clinical research, though it should not be used for individual treatment decisions as ICU outcomes depend on many factors beyond the initial physiology score.
Formula
SAPS II = Sum of weighted points for 15 variables (age, HR, SBP, temp, PaO2/FiO2, urine output, BUN, WBC, K+, Na+, HCO3-, bilirubin, chronic diseases, admit type, GCS)
SAPS II is calculated using the worst physiological values within the first 24 hours of ICU admission. Each variable is scored independently using predefined point tables derived from logistic regression coefficients. The total score ranges from 0 to 163. The predicted hospital mortality probability is then calculated from the logistic regression equation: Logit = -7.7631 + 0.0737 × SAPS II score; Probability = exp(Logit) / (1 + exp(Logit)). This transforms the score into a percentage probability of hospital death ranging from <1% (score 0-5) to >90% (score >140).
Score Interpretation
SAPS II is one of the most widely used ICU severity scores globally, employed for benchmarking ICU performance, stratifying patients for clinical trials, and adjusting for case mix in comparative effectiveness research. It was developed from a large, diverse international database ensuring broad generalizability. While it provides accurate population-level mortality predictions, its use for individual patient prognostication is limited. The score should be calculated using the worst values within the first 24 hours of ICU admission and is not designed for serial reassessment. SAPS II has been validated in multiple countries and ICU types (medical, surgical, mixed) and is included in many national ICU audit programs.
Low Mortality Risk — 0–29
SAPS II 0-29. Predicted hospital mortality <15%.
Management: Continue standard ICU care.
Moderate Mortality Risk — 30–53
SAPS II 30-53. Predicted hospital mortality 15-40%.
Management: Close ICU monitoring. Multidisciplinary team review.
High Mortality Risk — 54–72
SAPS II 54-72. Predicted hospital mortality 40-70%.
Management: Intensive monitoring. Consider specialist consultation. Discuss goals of care.
Very High Mortality Risk — 73+
SAPS II 73-163. Predicted hospital mortality >70%.
Management: Maximal ICU support. Multidisciplinary involvement. Discuss prognosis and goals of care with family.
Reference Ranges
| Population | Normal Range | Notes |
|---|---|---|
| Adult ICU patients (first 24h) | 0-163 points | Higher scores = higher predicted mortality. Use worst values in first 24h of ICU admission. |
Dr. Khaled Hassan
Dr. Khaled is a cardiology consultant with experience in acute cardiac care.
View medical review board & editorial policy →Example Calculation
A 72-year-old man is admitted to ICU with septic shock from pneumonia. Worst values in first 24 hours: age 72 (16 pts), HR 135 (4 pts), SBP 70 (13 pts), temp 39.6°C (3 pts), on ventilator with P/F 150 (9 pts), urine output 350 mL (11 pts), BUN 54 mg/dL (6 pts), WBC 21 (3 pts), K 3.2 (3 pts), Na 151 (1 pt), HCO3 13 (6 pts), bili 3.2 (0 pts), no chronic disease (0), admit type medical (6 pts), GCS 9 (13 pts). Total SAPS II: 94 points. Predicted mortality: Logit = -7.7631 + 0.0737 × 94 = -0.835, probability = e^(-0.835)/(1+e^(-0.835)) = 0.303 = 30.3%. Interpretation: Very high mortality risk category.
Related Conditions
Related Medications
Common Mistakes
Calculating SAPS II using best values instead of worst values
SAPS II must be calculated using the worst (most abnormal) values within the first 24 hours of ICU admission. Using best values will underestimate mortality risk.
Recalculating SAPS II on subsequent days
SAPS II is designed for a single calculation using the first 24 hours of ICU admission. For serial assessment, use scores like SOFA or APACHE daily predictions.
Frequently Asked Questions
What is the difference between SAPS II and APACHE II?
Can SAPS II be used in all ICU patients?
References
- Le Gall JR, Lemeshow S, Saulnier F. A new Simplified Acute Physiology Score (SAPS II) based on a European/North American multicenter study. JAMA. 1993;270(24):2957-2963. PubMed
- Le Gall JR, Neumann A, Hemery F, et al. Mortality prediction using SAPS II: an update for French intensive care units. Crit Care. 2005;9(6):R645-R652. PubMed
- Capuzzo M, Scaramuzza A, Vaccarini R, et al. Validation of SAPS II in a cohort of Italian ICU patients. Intensive Care Med. 2000;26(11):1626-1633. PubMed
- SCCM/ESICM Guidelines for ICU Admission, Discharge, and Triage (2024)