Intensive care units (ICUs) are people- and technology-intensive environments where timely and wise use of advanced monitoring and life support is crucial to revert or avoid life-threatening conditions. From their inception, this highly complex environment has been confronted with a need to demonstrate its effectiveness to healthcare stakeholders . In the 1970s and 80s, increasing costs of intensive care, associated with poor outcomes of patients with multi-organ failure, urged intensivists and healthcare managers to look for metrics could concisely express ‘severity of illness’ and, thus, allow measurement of risk-adjusted outcomes .
In the early 1980s, the Acute Physiology and Chronic Health Evaluation (APACHE) system was a milestone in the history of ICU outcome prediction. This scoring system translated domains of pre-morbid conditions (age and co-morbidities), diagnoses and early physiologic derangements (organ failures, laboratory and physiological abnormalities) into a numeric expression of illness severity. In addition to the absolute value of the score, the APACHE system provided an estimate of the risk of death for each individual patient. APACHE was soon followed by the development of the Mortality Prediction Model (MPM) in the United States and the Simplified Acute Physiology Score (SAPS) in Europe. As the technologies improved, new treatments and protocols of care were applied, and the case-mix of the ICU changed (more elderly, co-morbidities and immunocompromised), scores needed to be updated to remain valid predictors of outcomes. The pioneering early versions of APACHE, SAPS and MPM were updated, with SAPS3, APACHE IV, and MPM0-III published, respectively, in 2005, 2006, and 2007 . One of the important differences among these scores relates to the time when they are calculated. SAPS3 and MPM0-III use data from the first hour of ICU admission; whereas, APACHE IV uses the “worst” measurements from the first 24 h. Therefore SAPS3/MPM0-III potentially reflects the early severity of the non-resuscitated patient. APACHE IV provides more time for data collection and less missing data.
Finally, dynamic scores may be applied in the ICU. The most commonly used is the Sequential Organ Failure Assessment (SOFA) which was developed to define the degree of organ failure, to stratify risk particularly in patients with sepsis, and to monitor response to treatment. Scoring systems, although useful for individual risk assessment, are not as applicable for mortality prediction and ICU performance monitoring. They are often used to complement more general mortality scores in ICU.