Free APACHE II Calculator

The APACHE II (Acute Physiology and Chronic Health Evaluation II) scoring system is a cornerstone of critical care assessment, designed to evaluate the severity of illness in ICU patients and predict hospital mortality. The APACHE II calculator computes a mortality score based on 16 clinical variables collected during the first 24 hours of ICU admission, covering age, chronic health conditions, and acute physiological derangements. This tool assists clinicians in stratifying patients by risk, guiding therapeutic decisions, and benchmarking outcomes across intensive care units.

What Is the APACHE II Score?

First introduced in 1981, the APACHE II system has become one of the most extensively validated ICU mortality scores. It assigns points to three main domains: age, chronic health status (including severe organ insufficiency or immunocompromise), and 12 acute physiological measurements. The total score ranges from 0 to 71, with higher values indicating greater severity. By converting the total score into a predicted mortality percentage, the system helps healthcare providers identify high‑risk patients early and allocate resources accordingly.

Using the APACHE II Calculator

All 16 input fields must be completed before the calculator can produce the APACHE II score and its associated mortality prediction. These inputs are grouped into three categories:

• Patient characteristics – age (16 years or older) and history of severe organ insufficiency (e.g., NYHA class IV heart failure, chronic dialysis, liver cirrhosis, or immunocompromised states) together with the surgical status (nonoperative, elective postoperative, or emergency postoperative).
• Examination findings – rectal temperature, Glasgow Coma Scale (GCS) score, mean arterial pressure (MAP), heart rate, respiratory rate, and oxygenation indices (A‑a gradient or PaO₂ depending on FiO₂).
• Laboratory test results – hematocrit, white blood cell count, arterial pH, serum potassium, serum sodium, and creatinine (differentiating acute vs. chronic renal failure).

Key Points for Each Input

• Age: The scoring system is intended for patients over 16 years. The score increases with advancing age.
• Chronic health: If the patient has a documented severe organ insufficiency or is immunocompromised, additional points are awarded based on whether surgery was elective, emergency, or not performed.
• Temperature: Provide the core body temperature in either Celsius or Fahrenheit.
• Glasgow Coma Scale: Enter the total GCS score (3–15). In the APACHE II system, the GCS contributes to the acute physiology score.
• Mean Arterial Pressure: Compute from systolic and diastolic pressures using: $$\text{MAP} = \frac{1}{3} \times \text{SBP} + \frac{2}{3} \times \text{DBP}$$
• Heart rate: Input in beats per minute (bpm). For irregular rhythms, count over 15 seconds and multiply by 4.
• Respiratory rate: Measure breaths per minute.
• Oxygenation: If FiO₂ is 50% or higher, use the alveolar‑arterial (A‑a) gradient; if FiO₂ is below 50%, use PaO₂.
• Hematocrit: Normal range approximately 36–51%. Deviations attract points.
• White blood cell count: Provide in thousands per cubic milliliter. Values above 10,000 may indicate infection or severe trauma.
• Arterial pH: Ideally between 7.33–7.50. Acidosis or alkalosis yields more points.
• Potassium & sodium: Units in mmol/L or mEq/L (1:1 conversion). Both high and low values are scored.
• Creatinine: Measured in mg/dL or µmol/L. The scoring depends on whether renal failure is acute or chronic.

APACHE II Scoring Tables

The tables below list the point assignments for each variable. The total APACHE II score is the sum of points from all three categories.

1. Patient Characteristics

Age Points

Age Range (years)	Points
44 or younger	0
45–54	2
55–64	3
65–74	5
75 or older	6

Chronic Health Points

History of Severe Organ Insufficiency / Immunocompromise	Points
Yes – nonoperative or emergency postoperative patient	5
Yes – elective postoperative patient	2
No	0

2. Examination Findings

Temperature

Core Temperature (°C)	Points
41.0 or higher	4
39.0–40.9	3
38.5–38.9	1
36.0–38.4	0
34.0–35.9	1
32.0–33.9	2
30.0–31.9	3
Below 30.0	4

Glasgow Coma Scale

GCS Score	Points
3–15	15

Mean Arterial Pressure (mmHg)

MAP (mmHg)	Points
160 or higher	4
130–159	3
110–129	2
70–109	0
50–69	2
49 or lower	4

Heart Rate (bpm)

Heart Rate (bpm)	Points
180 or higher	4
140–179	3
110–139	2
70–109	0
55–69	2
40–54	3
Below 40	4

Respiratory Rate (breaths/min)

RR (breaths/min)	Points
50 or higher	4
35–49	3
25–34	1
12–24	0
10–11	1
6–9	2
Below 6	4

Oxygenation

Condition	Parameter Range	Points
FiO₂ ≥ 50%	A‑a gradient >499	4
	A‑a gradient 350–499	3
	A‑a gradient 200–349	2
	A‑a gradient <200	0
FiO₂ < 50%	PaO₂ >70 mmHg	0
	PaO₂ 61–70 mmHg	1
	PaO₂ 55–60 mmHg	3
	PaO₂ <55 mmHg	4

3. Laboratory Test Results

Hematocrit (%)

Hematocrit (%)	Points
60 or higher	4
50–59	2
46–49	1
30–45	0
20–29	2
Below 20	4

White Blood Count (×10³/mm³)

WBC (×10³/mm³)	Points
40 or higher	4
20–39	2
15–19	1
3–14	0
1–2.9	2
Below 1	4

Arterial pH

Arterial pH	Points
7.70 or higher	4
7.60–7.69	3
7.50–7.59	1
7.33–7.49	0
7.25–7.32	2
7.15–7.24	3
Below 7.15	4

Serum Potassium (mmol/L)

Potassium (mmol/L)	Points
7.0 or higher	4
6.0–6.9	3
5.5–5.9	1
3.5–5.4	0
3.0–3.4	1
2.5–2.9	2
Below 2.5	4

Serum Sodium (mmol/L)

Sodium (mmol/L)	Points
180 or higher	4
160–179	3
155–159	2
150–154	1
130–149	0
120–129	2
111–119	3
111 or lower	4

Creatinine (mg/dL) – with renal failure status

Creatinine (mg/dL)	Renal Failure Status	Points
3.5 or higher	Acute	8
2.0–3.4	Acute	6
1.5–1.9	Acute	4
3.5 or higher	Chronic	4
2.0–3.4	Chronic	3
1.5–1.9	Chronic	2
0.6–1.4	Chronic or acute	0
Below 0.6	Chronic or acute	2

Important Considerations

• The APACHE II score is intended for patients aged 16 years and older. The most reliable estimate is obtained when all variables are measured within the first 24 hours of ICU admission.
• This calculator produces an estimation based on the original APACHE II model. Always interpret results in the context of the patient’s overall condition and clinical judgment.
• The tool is designed for educational and reference purposes and should never replace a thorough medical assessment by a qualified healthcare professional. For any health concerns, consult a physician.