Background Interruptions and multitasking are implicated as a major cause of clinical inefficiency and error.

Objective The aim was to measure the association between emergency doctors' rates of interruption and task completion times and rates.

Methods The authors conducted a prospective observational time and motion study in the emergency department of a 400-bed teaching hospital. Forty doctors (91% of medical staff) were observed for 210.45 h on weekdays. The authors calculated the time on task (TOT); the relationship between TOT and interruptions; and the proportion of time in work task categories. Length-biased sampling was controlled for.

Results Doctors were interrupted 6.6 times/h. 11% of all tasks were interrupted, 3.3% more than once. Doctors multitasked for 12.8% of time. The mean TOT was 1:26 min. Interruptions were associated with a significant increase in TOT. However, when length-biased sampling was accounted for, interrupted tasks were unexpectedly completed in a shorter time than uninterrupted tasks. Doctors failed to return to 18.5% (95% CI 15.9% to 21.1%) of interrupted tasks.

Conclusions It appears that in busy interrupt-driven clinical environments, clinicians reduce the time they spend on clinical tasks if they experience interruptions, and may delay or fail to return to a significant portion of interrupted tasks. Task shortening may occur because interrupted tasks are truncated to ‘catch up’ for lost time, which may have significant implications for patient safety.