In many hospitals operating room (OR) utilization rates and turnover times (the time from the end of the previous surgical procedure to the beginning of the next) are used as indicators of OR workflow inefficiency. However, there have been no detailed studies to determine whether these indicators really provide an adequate picture of avoidable wasting of time in the OR.All relevant OR processes in a busy surgical suite with nine ORs were studied in detail over an 8-week period. Productive OR processes, and also reasons for unused times, were recorded by independent observers at 5-minute intervals; they were able to code for 10 different productive activities and 20 different reasons for unused time. Unused time in the OR, the OR utilization rate and the average perioperative turnover times were calculated for each day and a correlation analysis was performed.In all, 3,501 OR hours and 790 surgical cases were studied. Productive processes accounted for 85.7% of the total OR time; the unused times were times with no scheduled cases (7.7%) and waiting times that arose for many different reasons (6.6%). Correlation analysis showed that there was no close correlation between waiting time and OR utilization (Spearman's r(s) 0.104 and r(s) 0.233). The correlations between total unused time (r(s) 0.718 and r(s) 0.745) and time with no scheduled cases (r(s) 0.706 and r(s) 0.620) and utilization were more robust, but for any given OR utilization rate the range of corresponding unused time or time without scheduled cases per day was considerable. The correlation between waiting time and perioperative turnover times was negligible (r(s) 0.185 and r(s) 0.175). When different definitions of utilization rate or perioperative turnover were used the results obtained were virtually identical.Utilization rate and perioperative turnover time cannot be used as indicators of OR workflow efficiency, since they cannot identify the days during which avoidable waiting times occur. If the aim is to identify underused OR time and factors that hamper workflow efficiency, waiting times and times without scheduled cases need to be recorded directly and separately.
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