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APACHE is a short form for Acute Physiology and Chronic Health Evaluation.
APACHE is a scoring system that's commonly used in the Intensive care unit for predicting how severe a patient’s condition is.
The APACHE score was introduced in 1981 by the Medical Center of George Washington University and a popular scale in the Intensive Care Unit. There are several versions of APACHE score - like an update of an earlier version. The most current version is APACHE IV which was published in 2006(1).
This scoring system has a high level of accuracy in predicting the mortality rate and length of stay in patients. By using this scoring system, doctors can allocate and categorize the emergency needs for a patient. Especially during COVID- 19 conditions when there was a crisis for ICU beds and in need of resource allocation, APACHE II played a major role in allocation of hospital beds and in predicting mortality risk in patients(2, 3).
Differences in Version
Some of the differences between APACHE score versions are mentioned below.
APACHE I score used 34 variables for scoring whereas APACHE II uses 12 variables, Apache II score was revised in 1985 and 12 variables were selected among the 34 variables using multivariate analysis. APACHE III introduced in 1991 was based on 17 variables and APACHE IV was introduced in 2006 after reformulating the APACHE III equations and this model uses the first 48 hours of ICU admission and predicts the patient's survival. Even though APACHE IV is the latest version, APACHE II is the most commonly used scoring system as APACHE II has better prediction results(4).
How is the APACHE II Score calculated?
APACHE II score takes into account acute physiological variables, age variable and chronic health condition. The scoring is done within 24 hours of ICU admission.
A. Physiological variables
There are 12 physiological variables that's scored based on the acute condition. They are -
i. Temperature
ii. Mean arterial pressure
iii.Heart rate
iv.Respiratory rate
v.Oxygenation
vi.Acid base balance
vii. Sodium
viii.Potassium
ix. Creatinine
x. Hematocrit
xi. White blood cell count
xii. Glasgow coma scale
The variables are selected in such a way that it covers all the important organs whose deterioration and failure can increase mortality risk. All these variables are important biomarkers to check the functionality of organs like heart, lungs, kidney, liver, brain function.
The points distribution is shown in Table 1.
B. Age Variable
Age plays a major factor in selecting treatment protocols but it cannot be used individually to predict mortality.
The age points assigned increase with age.
The age points assigned in APACHE II Score are as follows-
-Age <=44 has score 0
-Age <=45 and Age >=54 has score 2
-Age<=55 and Age>=64 has score 3
-Age <=65 and Age >=74 has score 5
-Age>=75 has score 6
C. Chronic Health Points
Chronic condition means the patient has been suffering from the condition for a long time. Here, the main focus is on weakened immune systems, history of organ dysfunction and also their operative history.
If patients suffering from immunocompromisation or organ failure and they had no operations or had any emergency post-operative conditions then they have been assigned score 5.
If patients suffering from immunocompromisation or organ failure had elected to get operated before worsening, then they have been assigned score 2.
Table 1: - Scoring system explained for APACHE II Score
Once after each physiological variable is scored, they are added together to get a physiological score value (A) . And, this value gets added with the age points and chronic health points to get the final value which is the APACHE II Score. This final value can vary from 0 to 71. 0 being the normal condition with normal values, whereas 71 score indicating high mortality risk and organ failure.
APACHE II Score and Mortality Prediction
APACHE II Score is considered to be an early warning predictor for mortality. Higher the scores, higher is the mortality risk for that individual.
I found a research article that has done a study to understand the mortality prediction by APACHE II score. The article " A critical study of the APACHE II scoring system using earlier data collection" had more than 2000 citations which means this article has been used as a reference in other related articles.
The study collected information on 756 patients admitted to general intensive care and calculated the APACHE II score and categorized the score in the interval of 5. The mortality rate is also calculated using the number of alive and number of dead patients in that category. The following table has the information on the APACHE II score categories, number of total patients in each category and number of patient's alive or dead in each category along with the mortality rate.
Table 2-
When you notice the table, we can clearly see that higher the APACHE II Score is higher is the mortality risk . Also notice that the mortality rate is increasing gradually till the APACHE II score 20 and above 20 the mortality rate has abruptly increased to 75% and above APACHE II score 41, the mortality rate is 100%.
Limitations for APACHE II Score
The score was based on the first 24 hours upon admission, consequently, it does not consider factors like treatment protocol to accurately predict the mortality rate as successful treatments can have influence and reduce the risk of mortality in patients, this can lead to overestimation of initial mortality prediction(6).
APACHE II Score's Mortality prediction accuracy depends on the patient' s admission, their surgical history , self harm issues. As these factors are not included in the scoring system, the mortality risk can be underestimated.
Each scoring system has its own positive and negative sides, its always better to take into account the other scoring systems like SOFA (Sequential Organ Failure Assessment score), SAPS II (Simplified Acute Physiology Score) , APACHE III score (evaluates information on 48 hrs of admission) to increase the specificity of mortality prediction in intensive care units (6).
Conclusion
Despite the limitation, APACHE II Score is a valuable tool to assess severity of illness and to predict mortality risk based on data collected within 24 hours of hospital admission. It directs doctors in allocating the medical resources, particularly during crises by providing a comprehensive view of a patient's health status. Additionally, It can aid in deciding appropriate treatment protocol thereby optimizing patient's care.
References used
2.How should ICU beds be allocated during a crisis? Evidence from the COVID-19 pandemic
3. Validation of the Acute Physiology and Chronic Health Evaluation (APACHE) II Score in COVID-19 Patients Admitted to the Intensive Care Unit in Times of Resource Scarcity
4..Which model is superior in predicting ICU survival: artificial intelligence versus conventional approaches
5.A critical study of the APACHE II scoring system using earlier data collection
6.Comparison of the mortality prediction of different ICU scoring systems (APACHE II and III, SAPS II, and SOFA) in a single-center ICU subpopulation with acute respiratory distress syndrome