The structure of critical care transfer networks

Abstract

Rationale: Moving patients from low-performing hospitals to high-performing hospitals may improve patient outcomes. These transfers may be particularly important in critical care, where small relative improvements can yield substantial absolute changes in survival.

Objective: To characterize the existing critical care network in terms of the pattern of transfers.

Methods: In a retrospective cohort study, the nationwide 2005 Medicare fee-for-service claims were used to identify the interhospital transfer of critically ill patients, defined as instances where patients used critical care services in 2 temporally adjacent hospitalizations.

Measurements: We measured the characteristics of the interhospital transfer network and the extent to which intensive care unit patients are referred to each hospital in that network--a continuous quantitative measure at the hospital-level known as centrality. We evaluated associations between hospital centrality and organizational, medical, surgical, and radiologic capabilities.

Results: There were 47,820 transfers of critically ill patients among 3308 hospitals. 4.5% of all critical care stays of any length involved an interhospital critical care transfer. Hospitals transferred out to a mean of 4.4 other hospitals. More central hospital positions were associated with multiple indicators of increased capability. Hospital characteristics explained 40.7% of the variance in hospitals' centrality.

Conclusions: Critical care transfers are common, and traverse an informal but structured network. The centrality of a hospital is associated with increased capability in delivery of services, suggesting that existing transfers generally direct patients toward better resourced hospitals. Studies of this network promise further improvements in patient outcomes and efficiency of care.

Figure 1. Example of Calculation of Network Centrality

At left is a sample network, with all hospitals transferring the same number of patients. At right are the hospitals’ relative centrality.

Figure 2. Map of Transfer Network

Hospitals are shown at their latitude and longitude in a simple Cartesian projection. Node size is proportional to centrality. Line darkness is proportional to the number of transfers passing between the two hospitals. {A higher resolution copy of this image is available as a separate file}

Figure 3. Patterns of Connections

Panel (a) displays the number of other hospitals that transferred patients INTO each hospital, formally termed “In-Degree”. Equivalent data is presented in tabular form to the right. Both horizontal and vertical axis are logarithmic due to wide variation. Panel (b) shows the number of other hospitals to which each hospital transferred patients OUT, formally termed “Out-Degree”.