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Critical care severity scoring

APACHE II (Acute Physiology And Chronic Health Evaluation)

Enter the most abnormal values from the first 24 hours of ICU admission. The calculator computes the Acute Physiology Score, adds age and chronic health points, and provides interpretation guidance.

Rectal or core temperature.

If FiO₂ ≥ 0.5, enter A–a gradient; otherwise PaO₂ suffices.

Use pre-sedation value when possible.

Acute Physiology Score

0

  • temperature0
  • map0
  • heartRate0
  • respiratoryRate0
  • oxygenation0
  • arterialPh0
  • sodium0
  • potassium0
  • creatinine0
  • hematocrit0
  • wbc0
  • gcs0

Age points

0

Age bands: 45–54 (+2), 55–64 (+3), 65–74 (+5), ≥75 (+6).

Total APACHE II score

0

Includes chronic health adjustment (+0 points).

Lower predicted mortality

Scores below 10 correlate with lower mortality in many populations, yet vigilance is still required.

How to Use This Calculator

1

Collect values from the first 24 hours

APACHE II uses the most deranged physiologic measurements during the first ICU day. Document the timing of each value.

2

Enter pre-sedation neurologic status

When patients are sedated or intubated, use the Glasgow Coma Scale prior to sedation if available, or document assumptions.

3

Consider chronic health modifiers

Add chronic health points only for severe organ insufficiency (e.g., NYHA IV, Child C, dialysis, immunosuppression).

Formula

APACHE II score = Acute Physiology Score (APS) + Age points + Chronic Health points.

  • APS is the sum of 12 physiologic subscores (temperature, MAP, heart rate, respiratory rate, oxygenation, arterial pH or HCO₃⁻, sodium, potassium, creatinine, hematocrit, WBC, Glasgow Coma Scale adjustment).
  • Glasgow Coma Scale contribution = 15 − actual GCS.
  • Creatinine points are doubled when acute renal failure is present.
  • Chronic health: add 5 points for nonoperative/emergency postoperative patients, 2 points for elective postoperative, when severe organ insufficiency or immunocompromise exists.

Full Description

APACHE II (1985) remains a widely used ICU severity index. It predicts hospital mortality and allows benchmarking of ICU performance. The score incorporates acute derangements in cardiovascular, respiratory, metabolic, and neurologic variables, while accounting for age and chronic comorbidities. Higher scores reflect greater physiologic stress and correlate with mortality risk.

Limitations include data entry burden, performance drift over time, and reduced accuracy in specific populations (e.g., cardiac surgery, liver failure). APACHE II should complement—not replace—clinician judgement and disease-specific scores. Validate predictions with current outcome data, as true mortality varies with ICU resources, case mix, and advancements in care.

Frequently Asked Questions

What if some variables are missing?

Use the most normal value (zero points) when data are missing, but document the omission. Avoid assuming normality if clinical suspicion remains.

Can I substitute serum bicarbonate for arterial pH?

Yes. If pH is unavailable, use serum HCO₃⁻ with the original APACHE II scoring table by converting to the corresponding points.

How often should APACHE II be recalculated?

Traditionally, APACHE II uses only the first 24-hour data. Sequential scores can illustrate trends but were not originally validated for daily use.

Does APACHE II predict length of stay?

It primarily estimates mortality. Length of stay correlates imperfectly; use additional metrics for resource planning.