Does patient volume affect clinical outcomes in adult intensive care units?

This systematic review assessed if outcomes in adult intensive care units (ICUs) are related to hospital and ICU patient volume. A systematic search strategy was used to identify studies reporting on volume-outcome relationship in adult ICU patients till November 2010. Inclusion of articles was established through a predetermined protocol. Two reviewers assessed studies independently and data extraction was performed using standardized data extraction forms. A total of 254 articles were screened. Of these 25 were relevant to this study. After further evaluation a total of 13 studies including 596,259 patients across 1,068 ICUs met the inclusion criteria and were reviewed. All were observational cohort studies. Four of the studies included all admissions to ICU, five included mechanically ventilated patients, two reported on patients admitted with sepsis and one study each reported on patients admitted with medical diagnoses and post cardiac arrest patients admitted to ICU, respectively. There was a wide variability in the quantitative definition of volume and classification of hospitals and ICUs on this basis. Methodological heterogeneity amongst the studies precluded a formal meta-analysis. A trend towards favourable outcomes for high volume centres was observed in all studies. Risk-adjusted mortality rates revealed a survival advantage for a specific group of patients in high volume centres in ten studies but no significant difference in outcomes was evident in three studies. The results indicate that outcomes of certain subsets of ICU patients-especially those on mechanical ventilation, high-risk patients, and patients with severe sepsis-are better in high volume centres within the constraints of risk adjustments.