Scoring systems as a prognostic predictors:
Several objective systems based on statistically validated determinants of outcome have been developed during the last 15 years. In general, these system include physiologic variables, diagnosis, age and previous health status. Recently, measurement over time have been used to refine predictions from these systems(Osborne,1992). The ideal predictive scoring system would use objective, simply measured predictors. For prediction models to become universally accepted, not only will they have to be validated in terms of their predictive accuracy but they also need to be easily implemented in the ICU environment. The progressive automation of data collection in modern ICUs offer an opportunity to implement scoring systems into daily decision making(Kollef and Schuster,1994).
Classification of scoring systems:
(modified after Roberts and Zimmerman,1995)
1-Disease-specific severity systems e.g.:
*Acute myocardial infarction
*Adult respiratory distress syndrome(ARDS)
2-System-specific severity system e.g.: Glasgow Coma Scale Score(GCS) 3-General severity scoring systems e.g.:
*Therapeutic intervention scoring system(TISS)
*Acute Physiology and Chronic Health Evaluation(APACHE)systems: -original APACHE
*Simpified Acute Physiology Score (SAPS)and SAPS II
*Mortality Probability Model(MPM) and MPM II
*Multiple Organ Dysfunction/Failure scores
I-Disease specific severity systems:
Example:Adult respiratory distress syndrome(ARDS)
Murray et al.,(1988)designed a quantitative lung injury score which assigned points for each of four variables; extent of disease by chest roentgenogram, hypoxemia, lung compliance and level of required PEEP.
Identification of the associated illness also affect prognostic estimates because of variation in the natural history of ARDS in different disorders. The severity of non-pulmonary organ dysfunction provides an additional estimates of the prognosis; the more organ system failing, the higher the mortality. Which system or measure is the best predictor of mortality remains to be determined(Schuster,1995).
II-System-specific severity systems:
Example: Glasgow Coma Score(GCS)
Level of consciousness has been related to mortality risk in critically ill patients. The development of GCS in a group of head injury patients by Teasdale and Jennett(1974) provided a standard way of assessing neurologic status. Since its introduction, the use of GCS has been extended to the neurologic evaluation of wide variety of critically ill medical an surgical patients without head trauma. Clinicians now use the GCS routinely to assess critically ill patients. It is used as the only neurologic predictor in several general prognostic systems(Bastos et al.,1993).
Most authors use the GCS as a guide initially to define the coma state and then to follow sequentially the patient's neurologic response. Despite of the widespread use of GCS, its validity in patients with diagnosis other then trauma has been questioned(Cerra et al.,1990).
III-General severity scoring systems:
General severity scoring systems provide numerical scores that reflect severity of illness for ICU patients with a wide range of diagnosis. Weights are assigned to physiologic measures or therapeutic interventions; a rising score reflects an increasing severity of illness and higher death rate(Roberts and Zimmerman,1995).
Therapeutic Intervention Scoring System(TISS):
The TISS is based on the premise that regardless of the diagnosis, the more therapy the patients receives, the greater severity of illness (Rafkin,1991). TISS assigns a score ranging from 1 to 4 points to many of the diagnostic, monitoring and therapeutic interventions performed in the ICUs. The points...
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