Since the development of prognostic score systems in intensive care me
dicine in the 1980s score models have improved substantially and are n
ow based on much larger databases. They have been validated in many mu
lticenter and international studies all over the world. Prognostic sco
ring systems may be used for assessment of severity of illness, strati
fying patients prior to randomization in clinical trials, evaluation a
nd comparing outcome and survival (hospital mortality), quality assess
ment, cost-benefit analysis, and in clinical decision making. Validate
d time points for predicting hospital mortality of ICU patients are at
admission and at 24 hours. The relationship of the observed hospital
mortality rate to the estimated mortality provides the basis for clini
cal performance measurement. Since each ICU serves a different patient
population, each score system must be calibrated in the individual ho
spital to ensure that the model is applicable. General scores covering
more than one disease are Acute Physiology And Chronic Health Evaluat
ion (APACHE II, APACHE III), Simplified Acute Physiology Score (SAPS)
and Mortality Predicting Model (MPM). The Therapeutic Intervention Sco
ring System (TISS) and in part the Hannover Intensive Score (HIS) eval
uate exclusively the amount of medical therapy required. The TISS-Scor
e might serve as a possible measure of resource use for the ICU portio
n of the hospital stay. Disease (e.g. Trauma Score, Injury of Severity
Score) and patient (e.g. PRISM = Pediatric Risk of Mortality) specifi
c scores take into account the influence of disease and patient popula
tion in relation to outcome. They are not always of more predictive va
lue than general score models. Score models have been criticized for a
number of reasons. Outcome of ICU therapy should incorporate not only
survival but should also take into account quality of life, morbidity
and disability. Severity scores have no role in clinical decision mak
ing for an individual patient (e.g. patient triage for ICU admission,
discharge criteria, withdrawal of life support). This is due to the cu
rrent low sensitivity. Subsequent validation of variables could improv
e the sensitivity and the value of severity scoring in the future. Nev
ertheless, illness severity scores will never be indicative of absolut
e irreversibility of disease or impossibility of survival. Advances in
computer technology should assist in achieving many of the future goa
ls of prognostic scoring systems. Most of the physiological data are a
vailable from ICU monitors and computerized laboratory systems. By ele
ctronically interfacing with the ICU monitor an automated patient data
entry is possible and will provide that prognostic scores can be made
available to the clinician daily.