Apache II Calculator - ICU APS Plus Age And Chronic Health
apache ii score calculator using the 1985 Knaus Acute Physiology Score with age points, chronic health, and the published 0 to 71 mortality band.
Apache II Calculator
Results
What This Calculator Does
An APACHE II score calculator turns admission vitals, lab values, GCS, age, and chronic health status into a single 0 to 71 score paired with the 1985 Knaus hospital mortality band.
- • ICU admission review: drop in the first 24 hours of vitals, lab values, and GCS and read the total and mortality band on the same screen.
- • Critical care handoff: use the total as a one-line summary of admission severity when handing a patient to the next ICU team.
- • Quality and audit support: pair the total with a 1985 Knaus mortality band for ICU benchmarking and quality improvement projects.
The score is the most widely used ICU severity score, pairing a physiology-based sub-score from 12 admission variables with a small age adjustment and a chronic health adjustment.
The calculator is a planning tool. ICU triage, palliative care, and discharge planning sit with the critical care team.
The serum creatinine term mirrors the same kidney function question that the GFR Calculator answers with an estimated glomerular filtration rate from the same blood draw.
How This Calculator Works
The calculator works in three steps. It scores each of the 12 physiologic variables on a 0 to 4 scale using the 1985 Knaus bands, with the GCS contribution as 15 minus the actual GCS. It adds age points from the five-bucket table and chronic health points from the three-category table. It sums the three blocks and returns the 1985 Knaus hospital mortality band.
- Temperature: worst core temperature in degC, first 24 hours.
- MAP: worst mean arterial pressure in mmHg.
- Heart rate: worst heart rate in bpm.
- Respiratory rate: worst RR in breaths/min, ventilated or not.
- Oxygenation: A-a gradient (FiO2 >= 0.5) or PaO2 (FiO2 < 0.5) in mmHg.
- Arterial pH: worst arterial blood pH.
- Serum sodium: worst serum Na in mmol/L.
- Serum potassium: worst serum K in mmol/L.
- Serum creatinine: worst serum Cr in mg/dL. Points double if ARF.
- Hematocrit: worst hematocrit in percent.
- WBC: worst white blood cell count in 10^3 per microliter.
- GCS: Glasgow Coma Scale total. APS contribution is 15 minus the actual GCS.
Each physiologic variable is scored on the published 0 to 4 scale, the 12 contributions are summed, and the age and chronic health blocks are added on top.
The GCS contribution is 15 minus the actual GCS, and the creatinine points are doubled if the acute renal failure toggle is on.
Moderate severity 60-year-old non-op (APS 10, age 3, chronic 5, APACHE II total 18)
Temp 38.8, MAP 70, HR 120, RR 26, A-a 280, pH 7.35, Na 145, K 5.0, Cr 2.0 (no ARF), Hct 35, WBC 14, GCS 14, age 60, non-op
Temp 1, MAP 0, HR 2, RR 1, A-a 2, pH 0, Na 0, K 0, Cr 3, Hct 0, WBC 0, GCS 1. APS = 10. Age 60 (55-64) = 3. Chronic non-op = 5.
Total 18, ~11% hospital mortality band.
The physiology is moderately deranged, the patient is in the 55 to 64 age band, and the chronic health block is at its non-operative maximum. The total lands in the 15-19 band, mapping to roughly 11 percent hospital mortality.
According to Knaus et al., Critical Care Medicine 1985, the score is the sum of the Acute Physiology Score from 12 physiologic variables, age points, and chronic health points, with a total range of 0 to 71 and a published hospital mortality band by total.
According to Wikipedia, the score combines an acute physiology score from 12 admission variables with age points and chronic health points to predict hospital mortality for ICU admissions.
The mean arterial pressure column is built from systolic and diastolic readings, and the Blood Pressure Calculator returns the same MAP and pulse pressure from a single cuff reading.
Key Concepts Explained
Four concepts drive the result. Naming them keeps the APACHE II total from being read as a single lab number, which it is not.
Acute Physiology Score
the 0 to 4 point scoring of the 12 worst physiologic measurements in the first 24 hours, with the GCS contribution as 15 minus the actual GCS and creatinine points doubled in ARF. Contributes 0 to 60 points.
Age Points
0 to 6 point adjustment for patient age: 0 for at or below 44, 2 for 45 to 54, 3 for 55 to 64, 5 for 65 to 74, 6 for at or above 75.
Chronic Health Points
0, 2, or 5 point adjustment for severe organ insufficiency or immunocompromise. Elective post-operative: 2, non-operative or emergency post-operative: 5, none: 0.
1985 Knaus Mortality Band
the published 1985 Knaus table that maps the total to a hospital mortality percent, from roughly 1 percent in the 0 to 4 band to roughly 99 percent in the 65 plus band.
The total is built from three blocks, not a single number. The physiology block carries the most weight, the age block contributes a small adjustment, and the chronic health block is the smallest.
The heart rate column is one of the four vital sign rows in the Acute Physiology Score, and the ECG Heart Rate Calculator reads the same beats per minute from an ECG strip or pulse oximeter waveform.
How to Use This Calculator
The form works from a small set of admission measurements. Each input should be set to the worst value from the first 24 hours of ICU admission, not an averaged or normal value.
- 1 Enter the four vitals: type the worst temperature, MAP, heart rate, and respiratory rate from the first 24 hours.
- 2 Pick the oxygenation branch: select A-a gradient (FiO2 at or above 0.5) or PaO2 (FiO2 below 0.5) and enter the matching value in mmHg.
- 3 Enter the labs, GCS, and ARF: type the worst arterial pH, serum sodium, serum potassium, serum creatinine, hematocrit, WBC, GCS, and acute renal failure status.
- 4 Enter age and chronic health: type the patient age and pick the chronic health category (none, elective post-operative, or non-operative or emergency post-operative).
A reader with temp 38.8, MAP 70, HR 120, RR 26, A-a 280 on FiO2 0.5, pH 7.35, Na 145, K 5.0, Cr 2.0 without ARF, Hct 35, WBC 14, GCS 14, age 60, and non-op status can enter those values and read a total of 18 with an 11 percent mortality band.
Benefits of Using This Calculator
Calculating the APACHE II total from a small set of admission measurements has several practical benefits over running the scoring table by hand.
- • Three blocks, one form: a single form turns the 12 physiologic variables, age, and chronic health into a single 0 to 71 total and a published hospital mortality band.
- • Glasgow Coma Scale built in: the calculator returns 15 minus the actual GCS as the GCS contribution, so a GCS of 3 adds 12 points and a GCS of 15 adds 0 points.
- • Acute renal failure rule: the ARF toggle doubles the creatinine points, matching the published scoring rule for the renal component.
The same form works for a one-line summary at ICU admission and for a teaching reference that walks through the 1985 Knaus scoring rules without re-deriving the constant 0 to 4 scale by hand.
After the total is in hand, the next cardiovascular question is vascular age, and the Arterial Age Calculator converts the same risk factors into a vascular age that complements the mortality band.
Factors That Affect Your Results
Several factors shape the APACHE II total. The most important ones sit inside the entered form, and a small set of caveats belong outside the form.
Glasgow Coma Scale
the GCS contributes 15 minus the actual GCS as APS points, so a deeply sedated or comatose patient adds up to 12 points from GCS alone. The GCS term is the largest single APS contribution.
Oxygenation Branch
The score uses the A-a gradient when FiO2 is at or above 0.5, and PaO2 when FiO2 is below 0.5. Picking the wrong branch can move the oxygenation contribution by several APS points.
Acute Renal Failure
the ARF toggle doubles the creatinine points, so a creatinine of 2.5 mg/dL with ARF contributes 6 APS points and the same creatinine without ARF contributes 3 APS points.
- • The score was derived in 1985 and is calibrated to the published hospital mortality band for the original cohort. The 1985 mortality band is the most widely cited reference, but updated models such as APACHE IV are used in some centres for benchmarking.
- • The result is a planning estimate, not a clinical decision. ICU triage, palliative care, and discharge planning sit with the critical care team and should consider the total alongside symptoms, comorbidities, and the goals of care.
A total in the moderate band (15 to 19) or worse should be brought to the next ICU round with the trend of the admission vitals and the goals of care.
According to Cleveland Clinic, the score is used at ICU admission to estimate hospital mortality from a small set of admission physiologic measurements, age, and chronic health status.
As an admission severity score rather than a chronic risk tool, pairing the total with a current lipid panel is a sensible follow-up, and the LDL Calculator converts total cholesterol, HDL, and triglycerides into an LDL estimate in the same workflow.
Frequently Asked Questions
Q: What is a normal APACHE II score?
A: A normal APACHE II total for a previously healthy 40-year-old elective post-operative patient is 0, and a total below 5 maps to roughly a 1 percent hospital mortality band in the 1985 Knaus table. The total is 0 to 71, so a low single-digit value means the admission physiology, age, and chronic health are all within the normal band.
Q: How is the APACHE II score calculated?
A: The APACHE II score is the sum of three blocks. The first block is the Acute Physiology Score, which sums 0 to 4 points for each of the 12 worst physiologic measurements in the first 24 hours of ICU admission, with the Glasgow Coma Scale contribution calculated as 15 minus the actual GCS. The second block is age points (0 to 6 across five age bands). The third block is chronic health points (0, 2, or 5 depending on operative status). The total is 0 to 71.
Q: What are the 12 variables in the APACHE II score?
A: The 12 APACHE II Acute Physiology Score variables are core (rectal) temperature, mean arterial pressure, heart rate, respiratory rate, oxygenation (A-a gradient when FiO2 is at or above 0.5, or PaO2 when FiO2 is below 0.5), arterial pH, serum sodium, serum potassium, serum creatinine, hematocrit, white blood cell count, and the Glasgow Coma Scale. The creatinine points are doubled when acute renal failure is present.
Q: What is the mortality rate for each APACHE II band?
A: The 1985 Knaus hospital mortality table maps the total to a percent. 0-4 is about 1 percent, 5-9 is about 3 percent, 10-14 is about 6 percent, 15-19 is about 11 percent, 20-24 is about 19 percent, 25-29 is about 31 percent, 30-34 is about 44 percent, 35-39 is about 56 percent, 40-44 is about 67 percent, 45-49 is about 78 percent, 50-54 is about 88 percent, 55-59 is about 93 percent, 60-64 is about 96 percent, and at or above 65 is about 99 percent.
Q: What is the maximum APACHE II score?
A: The maximum APACHE II score is 71. The Acute Physiology Score contributes 0 to 60 across the 12 physiologic variables (the Glasgow Coma Scale contribution alone is 0 to 12, with all other variables at 0 to 4), age points contribute 0 to 6, and chronic health points contribute 0 to 5. The total 0 to 71 covers the full published range.