Question 11

List the desirable features of an Illness  Severity Scoring System for Intensive Care patients.? Compare and contrast the Acute Physiology and Chronic Health Evaluation (APACHE) and Sequential  Organ Failure Assessment (SOFA) scoring systems.

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College Answer

The ideal scoring system would have the following characteristics:

1.   Scores calculated on the basis of easily/routinely recordable variables
2.   Well calibrated
3.   A high level of discrimination
4.   Applicable to all patient populations in ICU
5.   Can be used in different countries
6.   The ability to predict mortality,functional status or quality of life after ICU discharge





Three factors that influence
outcome in critical illness- pre-existing disease, patient reserve and severity of
acute illness

Degree of organ
dysfunction related to acute illness (initially based of sepsis related organ dysfunction but later validated for organ dysfunction not related to sepsis


Physiological variables,
chronic health conditions and emergency /elective admissions and post- operative/non- operative admissions

Defined score ( 1-4) for
each of six organ systems- respiratory, CVS, CNS, Renal, coagulation and liver

Scoring duration

Based on the most abnormal
measurements in the first 24 hours of ICU stay

Daily scoring of individual
and composite scores possible during course of ICU stay

Population Outcome

Standardized mortality
ratios (SMR) (observed/predicted) can be used for large patient populations.

No predicted mortality
algorithm. In general higher SOFA score is associated with worse outcome.

Treatment effects on SOFA

Individual patient outcomes

Not possible to predict
individual patient outcome or response to therapy

Response of organ
dysfunction to therapy can be followed over time


The various illness severity scoring systems are summarised elsewhere.

LITFL gives the a list of qualities for the "ideal" ICU scoring system. In his 2010 review of scoring systems, Jean-Louis Vincent also gives this list of "ideal" features.

I have incorporated these opinions into one master list of ideal features.

  • Simple and inexpensive
  • Routinely available in all ICUs
  • Scores calculated on the basis of easily / routinely recordable variables
  • Reliable (intra and inter-observer)
  • Objective (that is, observer independent)
  • Specific to the function of the organ in question
  • Well calibrated and validated
  • A high level of discrimination
  • Therapy independent
  • Sequential (available at ICU admission or shortly thereafter and then at fixed periods of time)
  • Not affected by transient, reversible abnormalities associated with therapeutic or practical interventions 
  • Reflect acute dysfunction of the organ in question but not chronic dysfunction
  • Applicable to all patient populations in ICU
  • Reproducible in large, heterogeneous groups of ICU patients
  • Allows the comparison of groups in clinical trials
  • Reproducible in several types of ICUs from different regions of the globe
  • Abnormal in one direction only
  • Using continuous rather than dichotomous variables
  • Able to predict mortality, functional status or quality of life after ICU discharge

A comparison of SOFA and APACHE as a table is discussed in detail elsewhere; I will merely reproduce the comparsion table in the space below.

A Comparison of the SOFA and APACHE Scoring Systems



Basic premise

ICU mortality depends on three domains:

  • Premorbid health
  • Severity of illness
  • Patient's physiological reserve

Thus, if one can quantify these domains, one may be able to predict mortality on the basis of such measurements.

Degree of organ dysfunction is related to acute illness. Originally designed with sepsis in mind, but subsequently validated in other disease states.

Measured parameters

Heuristic groupings of 12 physiologic variables, Glasgow Coma Score (GCS), age, and chronic health evaluation status.

6 domains of organ system function

Measurement collection

Worst score within the first 24 hours

Daily measurement of

Unique features

Incorporates chronic illness, emergency admission, age, surgical vs non-surgical admission, and cardiorespiratory arrest

Incorporates the use of organ system support sug as vasopressors and dialysis


0 to 71

0 to 24

Mortality prediction

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%.

SOFA does not predict mortality, and the original authors intended it to be used as a means of reproduceably describing a sequence of complications in the critically ill.

That said, higher SOFA scores are in factassociated with increased mortality.

Prognostic value

APACHE is a poor predictor of individual patient outcome.

One can monitor response to therapy by the change of daily SOFA scores


Balci, C., et al. "[APACHE II, APACHE III, SOFA scoring systems, platelet counts and mortality in septic and nonseptic patients]." Ulusal travma ve acil cerrahi dergisi= Turkish journal of trauma & emergency surgery: TJTES 11.1 (2005): 29-34.

Halim, Dino Adrian, Tri Wahyu Murni, and Ike Sri Redjeki. "Comparison of Apache II, SOFA, and Modified SOFA scores in predicting mortality of surgical patients in intensive care unit at Dr. Hasan Sadikin General Hospital." Critical Care & Shock 12 (2009): 157-169.

Knaus, William A., et al. "APACHE II: a severity of disease classification system." Critical care medicine 13.10 (1985): 818-829.

Vincent, J-L., et al. "The SOFA (Sepsis-related Organ Failure Assessment) score to describe organ dysfunction/failure." Intensive care medicine 22.7 (1996): 707-710.

Ferreira, Flavio Lopes, et al. "Serial evaluation of the SOFA score to predict outcome in critically ill patients." Jama 286.14 (2001): 1754-1758.

Vincent, Jean-Louis, and Rui Moreno. "Clinical review: scoring systems in the critically ill." Crit Care 14.2 (2010): 207.

Livingston, Brian M., et al. "Assessment of the performance of five intensive care scoring models within a large Scottish database." Critical care medicine28.6 (2000): 1820-1827.

Wong, David T., et al. "Evaluation of predictive ability of APACHE II system and hospital outcome in Canadian intensive care unit patients." Critical care medicine 23.7 (1995): 1177-1183.