Background: To know the relative effect of external and internal factors on emergency department (ED) efficiency.
Patients and method: Along 3 consecutive weeks we compute at 3 hours-interval the number or patient waiting for visit and the mean waiting time for visit (efficiency markers), the number of patients arriving to ED (external pressure marker) and the number of patients remaining in ED after beginning the visit (internal pressure marker), which was divided in ED-related factors, hospital-related factors, ED-hospital interelation-related factors, or not caused by ED nor hospital-related factors.
Results: Only the increase of internal pressure was associated with a decline in ED efficiency (p < 0.001). ED-related and hospital-related factors were those significantly associated with such a decline (p < 0.05 and p < 0.01, respectively).
Conclusion: Internal pressure generated by the own ED exerts a prominent role in its dysfunction; therefore, policies addressed to reduce such internal pressure should be encouraged.