Page 130 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

96 PART 1: An Overview of the Approach to and Organization of Critical Care

difficult to find appropriate non-corticosteroid-treated patients to use little is known about accuracy of generalizations of scoring systems
as matched controls. to different categories of hospitals, hospitals from different countries
To demonstrate that there is a corticosteroid treatment effect, it is with different health care systems, or even different ICUs in the same
essential that a closely matched comparable non-corticosteroid-treated hospital. Therefore, we believe that use of scoring systems to compare
control group is selected. This control group is needed to be sure that ICU performance is limited and requires further evaluation.
differences between baseline clinical variables that were simply a pre- The fourth potential use of scoring systems is to assess individual
dictive (of treatment response) or a prognostic (of hospital mortality) patient prognosis and to guide care. We believe that scoring systems
do not account for and explain any observed difference in mortality. have limited use for individual patient prognosis and care decisions.
As shown in the literature, in clinical practice corticosteroids are often At best, they can guide physicians, families, and patients in difficult
given to younger patients with greater severity of disease and higher decisions. Patients’ preferences and patients’ quality of life prior to ICU
doses of norepinephrine. Therefore, simply comparing the mortality admission cannot be integrated into mathematical models. Severity-
rates in all corticosteroid-treated patients to all non-corticosteroid- of-illness scoring systems predict probability of mortality, but they are
treated patients in the cohort would be biased and invalid. For this not helpful in assessing probability of death in the 6 months following
example, we show how to use a design-based approach of matching cases discharge from the ICU. Finally, scoring systems do not predict quality
to controls to control for key baseline variables associated with risk of of life or return to independent living of patients.
death and with propensity to prescribe corticosteroids to yield a control We also recommend use of propensity scoring systems and case
sample that is directly comparable to the treated sample. This approach matching of patients in observational cohorts to simulate RCTs and so
optimizes efficient use of resources since only a subsample of all possible increase our understanding of the safety and efficacy of therapeutics
controls is needed for detailed evaluation. used clinically.
Other considerations arise if a cohort is multicenter. First, to control
for differences in standard of care across diverse geographic regions
and over time, matched patients would have to be selected within each
individual center from a contemporaneously enrolled population. The KEY REFERENCES
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It is recognized that this type of study uses convenience samples of clinical assessment with APACHE II for predicting mortality
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RECOMMENDATIONS FOR CLINICAL USE • Pollack MM, Ruttimann UE, Getson PR. Pediatric risk of mortality

There has been rapid growth in the number and types of severity- (PRISM) score. Crit Care Med. 1988;16:1110.
of-illness scoring systems in critical care, and they are increasingly • Raj R, Skrifvars MB, Bendel S, et al. Predicting six-month mortality
used for clinical research, administrative tasks, quality assurance, and of patients with traumatic brain injury: usefulness of common
individual patient prognosis. Therefore, physicians and administrators intensive care severity scores. Crit Care. 2014;18(2):R60.
must understand the principles underlying development and testing • Vincent JL, Moreno R, Takala J, et al. The SOFA (Sepsis-related
of these systems, as well as the sources of errors in their development, Organ Failure Assessment) score to describe organ dysfunc-
to interpret the literature and to decide how and which system to use. tion/failure. On behalf of the Working Group on Sepsis-Related
We recommend four uses of severity-of-illness scoring systems. First, Problems of the European Society of Intensive Care Medicine.
scoring systems are useful in clinical trials and in clinical research. The Intensive Care Med. 1996;22:707.
scoring system used must be validated and published in peer-reviewed
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Second, scoring systems may be used for administrative purposes,
to describe resource utilization relative to acuity of illness, and to assist
with resource-allocation decisions. REFERENCES
The third potential use of scoring systems is to assess ICU perfor-
mance. However, several biases limit this application because very Complete references available online at www.mhprofessional.com/hall

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