Threshold volumes associated with higher survival in health care - A systematic review

BACKGROUND. To date, systematic reviews on the relationship between the volume of specific diagnoses and procedures and patient outcomes have several limitations, including the omission of the most recent publications. OBJECTIVE. To investigate the relationship between hospital and physician volume and patient mortality rate for all diagnoses and interventions in health care. RESEARCH DESIGN. Medline and the Cochrane Library were searched from January 1990 to December 2000 for all studies published in Dutch, English, French, German, and Italian. The following Boolean search statement was used: hospitals AND volume AND (outcome OR mortality OR quality). Studies were included in which patient enrollment ended within 10 years of the current study and that were adjusted for case-mix. For each diagnosis and intervention, the study most likely to provide an unbiased estimate of the effect of volume on mortality rate was identified using a specific algorithm (best study). RESULTS. A total of 34 diagnoses and interventions with at least one qualifying study on the volume-outcome relationship were identified. The summary odds ratio/relative risk for the best studies on hospital and physician volume were 0.87 (95% confidence interval [CI], 0.85-0.89) and 0.87 (95% CI, 0.81-0.94), respectively. From the best studies on hospital volume, 48.5% (16 of 33) were published either in 1999 or 2000. CONCLUSIONS. There is evidence for a volume-mortality relationship for hospitals and physicians. The use of appropriate methods for analyzing additional diagnoses and interventions as well as a continuous systematic evaluation of the evidence is recommended.