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* From the Departments of Anesthesia and Health Management & Policy, University of Iowa, Iowa City, Iowa;
the Departments of Anesthesia and Health Research & Policy, Stanford University, Stanford, California;
the Department of Anesthesiology, Jefferson Medical College, Philadelphia, Pennsylvania; and
the Department of Management Sciences, University of Iowa, Iowa City, Iowa, USA.
Address correspondence to: Dr. Franklin Dexter, Division of Management Consulting, Department of Anesthesia, 6-JCP, University of Iowa, Iowa City, Iowa 52242, USA. Phone: 319-621-6360; Fax: 603-947-1304; E-mail: Franklin-Dexter{at}UIowa.edu
Purpose: Unbiased prediction of case durations is an integral part of matching operating room (OR) staffing to workload. Monitoring systematic bias in surgeons’ scheduled case durations can identify those services with estimates sufficiently inaccurate that statistical analysis of historical data may be useful in preference to the surgeons’ estimates. We describe a method to monitor surgical services’ average bias in scheduled case durations.
Methods: Actual case duration, predicted (scheduled) case duration, and service were obtained for all 58,291 cases during 39 four-week periods at an academic hospital. For each four-week period, a ratio was computed for each service. The numerator for each service equalled the sum of the differences in minutes between actual case duration and scheduled case duration. The denominator equalled the sum in hours of the actual durations of all of the service’s cases. The ratio was multiplied by eight hours to yield the number of minutes of underestimated case duration per eight hours of OR time during the four-week period.
Results: The ratios followed a normal distribution for each service. Using the Student’s t distribution, the 95% lower confidence bounds for the average underestimate of case duration ranged from three to 65 min per eight hours of used OR time.
Conclusions: To reduce over-utilized OR time, we recommend monitoring each service’s 95% lower confidence bound of the bias in scheduled case durations. For services consistently underestimating their case durations, schedule their cases using statistical estimates of case durations based on their historical data, and disregard their own estimates.
This article has been cited by other articles:
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  F. Dexter, E. U. Dexter, D. Masursky, and N. A. Nussmeier Systematic Review of General Thoracic Surgery Articles to Identify Predictors of Operating Room Case Durations Anesth. Analg., April 1, 2008; 106(4): 1232 - 1241. [Abstract] [Full Text] [PDF]
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 M. Olivares, C. Terwiesch, and L. Cassorla Structural Estimation of the Newsvendor Model: An Application to Reserving Operating Room Time Management Science, January 1, 2008; 54(1): 41 - 55. [Abstract] [PDF]
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F. Dexter, Y. Xiao, A. J. Dow, M. M. Strader, D. Ho, and R. E. Wachtel Coordination of Appointments for Anesthesia Care Outside of Operating Rooms Using an Enterprise-Wide Scheduling System Anesth. Analg., December 1, 2007; 105(6): 1701 - 1710. [Abstract] [Full Text] [PDF]
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C. McIntosh, F. Dexter, and R. H. Epstein The Impact of Service-Specific Staffing, Case Scheduling, Turnovers, and First-Case Starts on Anesthesia Group and Operating Room Productivity: A Tutorial Using Data from an Australian Hospital Anesth. Analg., December 1, 2006; 103(6): 1499 - 1516. [Abstract] [Full Text] [PDF]
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F. Dexter, J. C. Yue, and A. J. Dow Predicting anesthesia times for diagnostic and interventional radiological procedures. Anesth. Analg., May 1, 2006; 102(5): 1491 - 1500. [Abstract] [Full Text] [PDF]
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