Background: Institutional variation in the quality of medical care may be evaluated by examining process measures, such as use of diagnostic procedures or treatment modalities, or outcome measures, such as mortality. We undertook this study to examine variations in both process and outcome of care for patients with HIV-related Pneumocystis carinii pneumonia (PCP) at two geographically diverse, HIV-experienced, public municipal hospitals.
Design: Retrospective review of hospitalized patients diagnosed as having PCP cared for at two municipal hospitals from 1988 to 1990. At hospital A, charts of all patients diagnosed as having PCP were abstracted (n=209); at hospital B, a random sample of 15% were abstracted (=136).
Results: Among all hospitalized patients diagnosed as having PCP, the frequency of making a definitive diagnosis of PCP (as opposed to treating empirically) differed markedly at the two hospitals (85% in hospital A vs 26% in hospital B; p<0.001), as did the use of intensive care (18% vs 3%; p<0.001) and "do-not-resuscitate" orders (39% vs 14%; p<0.001), although the timing of starting anti-Pneumocystis medications (89% vs 88% within the first 2 hospital days) and the use of corticosteroids (21% vs 23%) were similar. Despite differences in the process of care, survival rates were similar at the two institutions (75% vs 76%; p=0.8) and remained similar when logistic regression was used to control for demographic variables and severity of illness (odds ratio for survival, hospital B vs A, 1.2 [95% confidence interval, 0.7, 2.0]). The 95% confidence intervals (0.7, 2.0), however, were consistent with a considerable (and clinically significant) disparity in survival (from 30% lower to a twofold higher odds of survival). Sample size calculations showed that a sample of 10 cases in each hospital would be required to detect the observed difference in definitive diagnosis rates (85% vs 26%), but 722 cases in each hospital would be required to detect a relevant difference in mortality.
Conclusions: The process of care for hospitalized patients with PCP in these two institutions differed considerably, but the survival rates were not significantly different, even after adjusting for confounding factors. While sample sizes available at the individual institutions were sufficient for evaluation of the process of care, they did not provide the power necessary to evaluate outcomes. Comparisons of outcomes such as mortality between individual hospitals may not have the statistical power to exclude important differences.