One method available to determine the duration of a case already under way is through Bayesian analysis . Bayesian analysis refers to the use of previous observations and current information to help determine future events. A computerized scheduling system that employs Bayesian analysis can transform scheduling by creating real-time decision support for the OR manager. Such a system may be able to make recommendations to an OR manager, such as: “Move the last case from OR 3 to OR 10” or “Have the on call team take over in room 8” [6].

Current real-time estimates can be supplemented by maintaining continuous communication with OR staff on the status of ongoing cases [6]. Regular updates are particularly valuable for longer cases and those with few historical comparisons [7, 8]. Approximately 20 % of surgeries in the United States are performed fewer than 1000 times per year and 36 % are performed less than once a year per surgical facility [6]. Therefore, building a database with enough prior historical case duration data becomes difficult.

Last 5 Case Estimate is a method of predicting durations when there is limited historical data [8]. This procedure-surgeon specific method averages the durations of the last five similar cases performed. For instance, if the surgeon has completed at least five similar cases in the past year, or barring that, if any surgeon has performed the same case, then those estimates are used to make current predictions. Over- or underestimations are closely associated with certain factors, such as if the case is an add-on, is performed after 5 PM, or is an outpatient procedure [8].

Another method of predicting case durations is to ask the surgeon to generate a time estimate [5]. However, their estimate may be biased due to a facility’s scheduling policies. For example, at some hospitals, surgeons may think it is necessary to provide shorter case time estimates to ensure that scheduled durations do not exceed the end of the regularly scheduled block time. Conversely, at another institution, a surgeon may be biased to lengthen case estimates to ensure that he/she does not lose block time to another surgeon.

One approach to improve inaccurate case duration predictions is to first identify high volume cases with highly variable case duration estimates (e.g., spine surgery or sinus surgery) and compute the percent deviation of actual time from scheduled time. The next step is to define the source of this variability. In other words, determine if the variability occurs due to clinical differences in surgery or if the data is inherently flawed. It is also imperative to investigate how the data is collected. Some electronic systems consider incision time to close time as the case duration, which then leads to future predictions based on that time frame. However, duration estimates should include a patient’s room enter to room exit time as well [5]. Defining the nonsurgical time frames, room in to incision and surgical closure to room out, can help improve scheduling accuracy.

Inaccuracies may also result from improper scheduling of the procedure type. Each case is defined not only by the type of procedure and the surgeon, but also by the facility site. This is because case times for the same procedure can differ in an ambulatory center versus an inpatient hospital surgery suite. Therefore, understanding the terminology used (e.g., are there incomplete procedures codes), having an appropriate user interface in computer scheduling programs, and adequately training scheduling personnel is imperative in accurately scheduling cases and producing time estimates.

Improving surgeon time estimates may occur by giving surgeons their own historical summary data and ensuring that they understand the terminology and the appropriate time frame estimates to use [5].

Generally, block times are given out in half or full block intervals that can range between 4 and 12 h [10]. Block lengths of 8–10 h are recommended, though, to allow for more cases to be accommodated and to improve overall efficient use of OR time [11]. Block time can be given to individual surgeons or surgical subspecialties as a whole [12]. However, assigning blocks to surgeons instead of whole services can increase efficiency and give surgeons a sense of ownership that encourages them to utilize their assigned time efficiently [11]. Other advantages of surgeon-specific block times include [10]:

Surgeon-specific block time can also be used to promote surgical growth by recruiting new surgeons and offering them dedicated block time. From a hospital’s perspective, block times for different surgeons can be spread out during the week to accommodate the use of limited surgical supplies (e.g., if there is only one robot, then surgeons who use it can be given blocks on different days so there is no conflict in use) [10].