College Answer

Scoring systems stratify groups of critically ill patients by severity, compare groups of patients in research trials, compare ICUs, and predict mortality for individuals and groups. Most measure physiological variables, some measure interventions. Derived by logistic regression from large demographic data sets of critically ill patients. Commonly used systems include:
•    APACHE II. Commonly used in Australia to measure patient severity. Uses 12 physiological variables and previous health estimate. Requires measure of worst values in first 24 hours in ICU, so affected if ICU admission delayed. Not reliable for predicting outcome in individuals. Limited by derivation from an historical data set.
•    APACHE III. Better outcome predictions by using additional variables and a more recent data set for comparisons. Outcome predictions for Australian patients more accurate.
•    GCS. Used to quantify severity of coma. Scale from 3-15. Eye (1-4), Verbal (1-5), and Motor (1-6) components. Key score for outcome prediction after head injury. Affected by alcohol and sedation. Should be scored in non-sedated non-paralysed patients.  Important component of other scoring systems eg APACHE 11.
•    TISS. System to score patient severity by counting procedures done. Less widely used.
Physician dependent, so less useful to compare ICUs.
•    SOFA. Organ dysfunction scores. Often a secondary endpoint in research trials.

Discussion

Here is a link to the LITFL article on ICU scoring systems.

Here are some links to the seminal articles which describe these systems:

• APACHE II
• SOFA
• TISS
• SAPS II
• MPM II
• POSSUM

So.

How are these scoring systems useful?

• They (try to) predict outcome and length of stay
• They can be used to compare predicted and observed outcome
• They stratify patients for clinical trials, according to disease severity
• They assess ICU performance
• They allow resources to be allocated to ICUs according to the illness severity of their patients
• They allow a comparison of ICUs

Some examples:

APACHE

APACHE stands for Acute Physiology, Age and Chronic Health Evaluation (I-IV).

• APACHE II is the most commonly used one
• 12 variables are measured
• Scores range from 0 to 71
• The risk of hospital death is computed by combining APACHE II score with Knaus' weighted coefficient for different types of disease entities. A score of 25 represents a predicted mortality of 50% and a score of over 35 represents a predicted mortality of 80%.
• Derived from histrical data set

SOFA

SOFA stands for Sequential Organ Failure Assessment .

• 6 organ systems are scored according to their function
• The degree of organ support is taken into account
• Used to analyse secondary endpoints in clinical trials

There is a defined score of 1-4 for each organ system, which is collected daily. This not a predictive model- there are no mortality algorithms here. A higher SOFA score can be said to relate to increased mortality, but there is no mathematical model to help us figure out exactly how the total score relates to survival.

TISS: Therapeutic Interventions Scoring System

• 76 variables (interventions and treatments)
• Collected daily
• Indicates nursing and medical workload
• Does not indicate severity of illness
• Most useful for accountants

SAPS: Simplified Acute Physiology Score

• SAPS 1 only looked at physiology, and was used by French ICUs
• SAPS 2 added chronic health conditions, and was used in Europe and North America
• SAPS 3 had 20 variables and was used worldwide

MPM: Mortality Prediction Models

• MPM measures variables at admission and in the first 24 hours
• It calcuates the risk of in-hospital death on the basis of these variables, using a logistic regression model.
• MPM II was based on the same historical data set as SAPS 2 and predicts mortality at 24, 48 and 7 hours.

POSSUM: = Physiological and Operative Severity Score for the enumeration of Mortality and Morbidity

• 12 physiological parameters for surgeons
• Used by surgeons as a risk adjustment tool
• Different subspecialties have their own: V-POSSUM is for vacular surgeons, Cr-POSSUM is for colorectal, etc