  Emergency department (ED) crowding has been an increasing problem worldwide.
Prior research has identified factors that contribute to ED crowding. However,
the relationships between these remain incompletely understood. This study's
objective was to analyse the effects of initiating a local protocol to
alleviate crowding situations at the expense of increasing returning patients
through the development of a system dynamics (SD) simulation model. The SD
study is from an academic care hospital in Boston, MA. Data sources include
direct observations, semi-structured interviews, archival data from October
2013, and peer-reviewed literature from the domains of emergency medicine and
management science. The SD model shows interrelations between inpatient
capacity restraints and return visits due to potential premature discharges.
The model reflects the vulnerability of the ED system when exposed to
unpredicted increases in demand. Default trigger values for the protocol are
tested to determine a balance between increased patient flows and the number of
returning patients. Baseline simulation runs for generic variables assessment
showed high leverage potential in bed assignment- and transfer times.
  A thorough understanding of the complex non-linear behaviour of causes and
effects of ED crowding is enabled through the use of SD. The vulnerability of
the system lies in the crucial interaction between the physical constraints and
the expedited patient flows through protocol activation. This study is an
example of how hospital managers can benefit from virtual scenario testing
within a safe simulation environment to immediately visualise the impacts of
policy adjustments.
