What APACHE II score predicts high mortality?

Non-operative patients: score 10–14 ~15% mortality; 15–19 ~25%; 20–24 ~40%; 25–29 ~55%; 30–34 ~75%; ≥ 35 ~85%. Post-operative patients generally have lower mortality at the same score. These estimates are from the original 1985 Knaus cohort and may differ from modern ICUs.

Which value should I use when parameters fluctuate?

Use the WORST (most abnormal) value recorded during the first 24 hours of ICU admission. For GCS, use the lowest score — but if the patient is sedated, score based on the estimated pre-sedation GCS or record as 15 per unit protocol (consult your institution's guideline).

How is oxygenation scored in APACHE II?

If FiO2 ≥ 0.5, use the A-aDO2 gradient (alveolar-arterial oxygen difference). If FiO2 70 = 0 pts; 61–70 = 1 pt; 55–60 = 3 pts; < 55 = 4 pts.

What is the difference between APACHE II and APACHE IV?

APACHE II (1985) uses 12 physiology variables and is simpler to compute manually; it remains the most widely cited. APACHE III (1991) and APACHE IV (2006) use more variables and refined regression models, offering better discrimination in modern cohorts but require proprietary software. APACHE II is still standard for many clinical trials.

Does a higher score always mean worse prognosis?

Generally yes — each additional point increases predicted mortality. However, APACHE II gives a population-level estimate, not an individual prediction. Many patients with high scores survive with aggressive treatment; conversely, complications unrelated to initial physiology can affect outcome. Always interpret in the full clinical context.

Is this calculator a substitute for clinical judgment?

No. This tool is for educational purposes only. APACHE II scores must be interpreted by qualified clinicians in the context of the complete patient presentation, trajectory, and institutional norms. Never use any score as the sole basis for treatment, triage, or withdrawal decisions.

APACHE II Score Calculator

Name: APACHE II Score Calculator
Availability: InStock
Author: Nham Vu

Enter 12 acute physiology variables plus age and chronic health points to calculate the APACHE II score and estimated in-hospital mortality.

For educational use only. Use the worst value from the first 24 hours of ICU admission. Not a substitute for clinical judgment — all scores must be interpreted by qualified clinicians.

A Acute Physiology Score (12 Variables)

Use the worst value recorded in the first 24 hours of ICU admission.

1. Rectal Temperature (°C)

Normal: 36–38.4 °C (0 pts)

2. Mean Arterial Pressure (mmHg)

Normal: 70–109 mmHg (0 pts). MAP = (SBP + 2 × DBP) / 3

3. Heart Rate (beats/min)

Normal: 70–109 bpm (0 pts)

4. Respiratory Rate (breaths/min)

Normal: 12–24 breaths/min (0 pts)

5. Oxygenation

FiO₂ (fraction, e.g. 0.21 for room air)

PaO₂ (mmHg) — if FiO₂ < 0.5

A-aDO₂ (mmHg) — if FiO₂ ≥ 0.5

Enter the value that applies based on your FiO₂. If FiO₂ ≥ 0.5, only A-aDO₂ is used.

6. Arterial pH

Normal: 7.33–7.49 (0 pts). Use serum HCO₃ only if ABG unavailable (not shown here).

7. Serum Sodium (mEq/L)

Normal: 130–149 mEq/L (0 pts)

8. Serum Potassium (mEq/L)

Normal: 3.5–5.4 mEq/L (0 pts)

9. Serum Creatinine (mg/dL)

Acute renal failure present (doubles creatinine score)

Normal: 0.6–1.4 mg/dL (0 pts)

10. Hematocrit (%)

Normal: 30–45.9% (0 pts)

11. White Blood Cell Count (×10³/mm³)

Normal: 3.0–14.9 ×10³/mm³ (0 pts)

12. Glasgow Coma Scale (GCS) — Total Score

Range 3–15. APACHE II GCS points = 15 − actual GCS. Use lowest recorded.

B Age Score

Patient Age (years)

< 44 yrs = 0 pts • 45–54 = 2 pts • 55–64 = 3 pts • 65–74 = 5 pts • ≥ 75 = 6 pts

C Chronic Health Score

Does the patient have evidence of severe organ system insufficiency or immunocompromised state (defined below)?

Liver: biopsy-proven cirrhosis with portal hypertension, episodes of past upper GI bleeding from portal hypertension, or prior episodes of hepatic failure/encephalopathy/coma Cardiovascular: New York Heart Association Class IV (severe) Respiratory: chronic restrictive, obstructive, or vascular disease resulting in severe exercise restriction (unable to climb stairs or perform household duties), or documented chronic hypoxia, hypercapnia, polycythemia, severe pulmonary hypertension (> 40 mmHg), or ventilator dependence Renal: receiving chronic dialysis Immunocompromised: receiving immunosuppressive therapy, chemotherapy, radiation, long-term or high-dose steroids, or has leukemia, lymphoma, or AIDS

Admission Type

Complete the parameters on the left
and click Calculate.

APACHE II Score — Predicted Mortality Reference

APACHE II Score	Non-operative Mortality	Post-operative Mortality	Risk Category
0–4	4%	1%	Very Low
5–9	8%	3%	Low
10–14	15%	7%	Low–Moderate
15–19	25%	12%	Moderate
20–24	40%	30%	High
25–29	55%	35%	High
30–34	75%	73%	Very High
≥ 35	85%	88%	Critical

Source: Knaus WA et al., Crit Care Med 1985. Mortality estimates reflect the original derivation cohort and may vary in modern ICUs.

Summary

Enter 12 acute physiology variables plus age and chronic health points to calculate the APACHE II score and estimated in-hospital mortality.

How it works

Enter each of the 12 acute physiology variables measured within the first 24 hours of ICU admission.
Select the worst (most abnormal) value recorded in that 24-hour window for each parameter.
Enter the patient's age to obtain the age-based contribution (0–6 points).
Select any applicable chronic health conditions (liver disease, cardiovascular, respiratory, renal, or immunocompromised).
Click Calculate to compute the Acute Physiology Score (APS), age score, chronic health score, and total APACHE II.
Review the estimated in-hospital mortality derived from the original Knaus et al. regression equation.

Use cases

Stratify ICU patient severity on admission and benchmark against unit averages.
Estimate predicted in-hospital mortality to guide goals-of-care and family discussions.
Risk-adjust ICU outcomes for quality-improvement research and inter-unit benchmarking.
Communicate patient acuity objectively between intensivists during handover.
Support triage decisions when ICU capacity is limited.
Educate medical students and residents on systematic critical illness assessment.
Evaluate eligibility for clinical trials that use APACHE II as an inclusion criterion.
Track physiological trajectory when calculated serially over the ICU stay.

Frequently Asked Questions

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Last updated: 2026-05-23 · Reviewed by Nham Vu