APACHE II Calculator

By Łucja Zaborowska, MD
Last updated: Jul 08, 2021

The APACHE II calculator allows you to compute the Intensive Care Unit (ICU) mortality rates for nonoperative and postoperative patients using their medical history, characteristics, physical examination, and laboratory test results.

Follow the article below to learn more about the APACHE score for ICU and its possible medical applications.

Read on - we will also cover the essential rules for assessing a patient's state and their comorbidities, according to the APACHE scoring system. 🧪

What is the APACHE II score?

The Acute Physiology And Chronic Health Evaluation II (APACHE II) score is one of the critical care scoring systems, developed in 1981.

Clinicians and health professionals worldwide use this system to assess the severity of a disease and the risk of death of an intensive care unit patient within the first 24 hours of admission.

The system allows us to apply the most suitable treatment and compare the morbidity and outcomes of different patients.

Try out our SAPS II calculator to find out more about the popular critical care scoring systems. 🩸

How to use the APACHE II calculator?

In this section, we'll explain all the details needed to properly evaluate of the APACHE 2 score and get the patient's predicted mortality.

The APACHE II calculator requires you to fill 16 empty fields, divided into three categories:

  • Patient's characteristics;
  • Present on examination; and
  • Laboratory tests results.
❗ Remember to fill in all the fields. You will not obtain your results until you provide all the informations needed.

  1. Age - this score is meant for people over 16 years of age.

  2. History of severe organ insufficiency:

    • If yes, did your patient require surgery? Choose between an elective and emergency operation.
    • You may also choose a non-surgical treatment for patients who suffered severe trauma but were not treated surgically.

    List of possible chronic organ insufficiencies:

    • NYHA IV - New York Heart Association Class IV Heart Failure;
    • Chronic dialysis;
    • Liver cirrhosis and its consequences - e.g., portal hypertension, esophageal bleeding, or encephalopathy; and
    • Immunocompromised patients - includes treatment such as chemotherapy and radiotherapy, and diseases such as leukemia and AIDS.
  3. Renal failure - evaluate the function of the kidneys.

    The physicians must use their clinical judgment to determine whether the patient suffers from the acute or chronic renal failure.

  4. Temperature - can be given in both metric and imperial units.

  5. Glasgow Coma Scale - points should consist between 3 and 15.

  6. Mean Arterial pressure (MAP) - can be calculated using the following formula: MAP = 1/3*(Systolic Blood Pressure) + 2/3*(Diastolic Blood Pressure).

  7. Heart rate - is given in beats per minute. (The best way to calculate this is to count the number of beats over 15 seconds and then multiply the result by 4.)

  8. Respiratory rate - count your patient's breaths over 1 minute.

  9. Oxygenation - FiO₂ level:

    • If your patient's FiO₂ is above or equal to 50%, use the A-a gradient in the next step; and
    • If your patient's FiO₂ is below 50%, use the PaO₂ (partial pressure of oxygen).
  10. Hematocrit - the percentage of red blood cells in the blood, ideally should consist between 36-51%.

  11. White blood cells, ideally given in thousands per cubic milliliter. A number above 10,000 indicates an ongoing infection or severe trauma.

  12. Arterial blood pH - should ideally be between 7.33-7.5.

  13. Potassium and Sodium levels can be given in either millimole per liter (mmol/L) or milliequivalent per liter (mEq/L). In this case, 1 mmol/L = 1 mEq/L.

  14. Creatinine - also evaluates the function of the kidneys.

Creatinine can be evaluated in two units: milligrams per deciliter (mg/dL) or micromoles per liter (μmol/L).

How to calculate APACHE II score?

This section will provide you with the number of points given for each category of the APACHE II score.

The patient's characteristics

Age, yearsNo. of points 
History of severe organ insufficiency/immunocompromised patient 
Yes: nonoperative/emergency postoperative patient5
Yes: elective postoperative patient2

On examination

Rectal temperature, °CNo. of points
39 to <413
38.5 to <391
36 to < 38.50
34 to <361
32 to <342
30 to <323
Glasgow Coma Scale (GCS) 
3-1515 - [GCS Score]
Mean arterial pressure, mmHg 
Heart rate, beats per minute 
140 to <1803
110 to <1402
70 to <1100
55 to <702
40 to <553
Respiratory rate, breaths per minute 
35 to <503
25 to <351
12 to <250
10 to <121
6 to <102
FiO₂ ≥ 50% 
A-a gradient >4994
A-a gradient 350-4993
A-a gradient 200-3492
A-a gradient <200 0
FiO₂ < 50% 
PaO2 >70 0
PaO2 = 61-701
PaO2 = 55-603
PaO2 <554

Laboratory test results

Hematocrit, %No. of points
50 to <602
46 to <501
30 to <460
20 to <302
White blood count/cubic millimeter (mm³)  
≥40 0004
20 000 to <40 0002
15 000 to <20 0001
3 000 to <15 0000
1 000 to <3 0002
<1 0004
Arterial pH 
7.60 to <7.703
7.50 to <7.601
7.33 to <7.500
7.25 to <7.332
7.15 to <7.253
Potassium, mmol/L 
6.0 to <7.03
5.5 to <6.01
3.5 to <5.50
3.0 to <3.51
2.5 to <3.02
Sodium, mmol/L 
160 to <1803
155 to <1602
150 to <1551
130 to <1500
120 to <1302
111 to <1203
Creatinine, mg/100 mL 
Acute renal failure: 
≥3.5 + acute renal failure*8
2.0 to <3.5 + acute renal failure6
1.5 to <2.0 + acute renal failure4
Chronic renal failure: 
≥3.5 + chronic renal failure4
2.0 to <3.5 + chronic renal failure3
1.5 to <2.0 + chronic renal failure2
0.6 to <1.50

Our APACHE II score calculator can be embedded into your page with the use of our widget, available below: ⤵️

Łucja Zaborowska, MD
Patient's characteristics
History of severe organ insufficiency
Renal failure
On examination
Glasgow Coma Scale
Mean arterial pressure
Heart rate
Respiratory rate
breaths per min
Lab tests
White blood count
Arterial pH
Potassium (K⁺)
Sodium (Na⁺)
Apache II Score
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