Lack of sensitivity of staffing for 8-hour sessions to standard deviation in daily actual hours of operating room time used for surgeons with long queues
BACKGROUND: At multiple facilities including some in the United Kingdom's National Health Service, the following are features of many surgical-anesthetic teams: i) there is sufficient workload for each operating room (OR) list to almost always be fully scheduled; ii) the workdays are organized such that a single surgeon is assigned to each block of time (usually 8 h); iii) one team is assigned per block; and iv) hardly ever would a team "split" to do cases in more than one OR simultaneously. METHODS: We used Monte-Carlo simulation using normal and Weibull distributions to estimate the times to complete lists of cases scheduled into such 8 h sessions. For each combination of mean and standard deviation, inefficiencies of use of OR time were determined for 10 h versus 8 h of staffing. RESULTS: When the mean actual hours of OR time used averages ≤8 h 25 min, 8 h of staffing has higher OR efficiency than 10 h for all combinations of standard deviation and relative cost of over-run to under-run. When mean ≤8 h 50 min, 10 h staffing has higher OR efficiency. For 8 h 25 min < mean <8 h 50 min, the economic break-even point depends on conditions. For example, break-even is: (a) 8 h 27 min for Weibull, standard deviation of 60 min and relative cost of over-run to under-run of 2.0 versus (b) 8 h 48 min for normal, standard deviation of 0 min and relative cost ratio of 1.50. Although the simplest decision rule would be to staff for 8 h if the mean workload is ≤8 h 40 min and to staff for 10 h otherwise, performance was poor. For example, for the Weibull distribution with mean 8 h 40 min, standard deviation 60 min, and relative cost ratio of 2.00, the inefficiency of use of OR time would be 34% larger if staffing were planned for 8 h instead of 10 h. CONCLUSIONS: For surgical teams with 8 h sessions, use the following decision rule for anesthesiology and OR nurse staffing. If actual hours of OR time used averages ≤8 h 25 min, plan 8 h staffing. If average ≤8 h 50 min, plan 10 h staffing. For averages in between, perform the full analysis of McIntosh et al. (Anesth Analg 2006;103:1499-516). © 2009 International Anesthesia Research Society.