We determine the effect of crowding on emergency department (ED) waiting room, treatment,
and boarding times across multiple sites and acuity groups.
This was a retrospective cohort study that included ED visit and inpatient medicine
occupancy data for a 1-year period at 4 EDs. We measured crowding at 30-minute intervals
throughout each patient's ED stay. We estimated the effect of crowding on waiting
room time, treatment time, and boarding time separately, using discrete-time survival
analysis with time-dependent crowding measures (ie, number waiting, number being treated,
number boarding, and inpatient medicine occupancy rate), controlling for patient demographic
and clinical characteristics.
Crowding substantially delayed patients' waiting room and boarding times but not treatment
time. During the day shift, when the number boarding increased from the 50th to the
90th percentile, the adjusted median waiting room time (range 26 to 70 minutes) increased
by 6% to 78% (range 33 to 82 minutes), and the adjusted median boarding time (range
250 to 626 minutes) increased by 15% to 47% (range 288 to 921 minutes), depending
on the site. Crowding delayed the care of high-acuity level 2 patients at all sites.
During crowded periods (ie, 90%), the adjusted median waiting room times of high-acuity
level 2 patients were 3% to 35% higher than during normal periods, depending on the
site and crowding measure.
Using discrete-time survival analysis, we were able to dynamically measure crowding
throughout each patient's ED visit and demonstrate its deleterious effect on the timeliness
of emergency care, even for high-acuity patients.