The therapeutic efficacy of critical care units from two perspectives: A traditional cohort approach vs a new case-control methodology

Abstract

The therapeutic efficacy of critical care units—whether they do more good than harm and for whom—has not been established, except for patients who are admitted for life-sustaining interventions, such as mechanical support of ventilation. However, most patients are admitted for observation, and to facilitate intervention if deterioration occurs or complications develop. The objective of this study was to determine whether direct admission to critical care units reduced mortality rates.

The population under study consisted of all 604 patients admitted to the medical service during a one month period. At the time of admission, the responsible residents rated patients as to how sick and stable they were. These ratings of illness severity and stability have been shown to be the most significant predictors of in-hospital mortality and morbidity, respectively; they were employed to stratify the patients prognostically.

The first analysis utilized the entire cohort of 604 patients. After patients who would have been ineligible for entry into a trial were removed, direct admission to the unit was associated with a reduced mortality in only one group of patients: the unstable, moderately ill (p < 0.05). “Unstable, severely ill” patients had high mortality rates when admitted to the floor or units, and stable patients (mildly or moderately ill) did equally well when admitted to either location. A further analysis revealed a possible explanation for these findings. Among the unstable, moderately ill patients, the rate of deterioration of pre-existing problems was significantly lower among patients directly admitted to the unit (p < 0.05), whereas the rate of new complications did not differ. Thus, in unstable, moderately ill patients, direct admission to the unit may reduce mortality by preventing deterioration of pre-existing problems.

The second analysis employed a new method of assessing therapeutic efficacy in which the scientific principles of a randomized trial design are applied to a case-control design. From the original cohort, the 66 fatalities (cases) were matched to 66 survivors (controls): from both groups, patients who would not have been eligible for a randomized trial of admission to critical care units were removed. Patients were then stratified by stability and severity, and the findings were quite similar to those in the cohort study. Direct admission to the unit had a protective effect in only one group of patients: unstable patients who were moderately ill. The concordance of the findings of the new case-control methodology with the trends in the cohort as a whole lends support to the validity of this new methodology for assessment of therapeutic efficacy.

Direct admission to the unit had a protective effect for patients who are unstable and moderately ill. Since many such patients are currently admitted to the floor, a randomized trial could be done in this group of patients to confirm the findings.