Table 4.

Characteristics and summary findings of the included optimization studies.

Study	Decision level	Schedule optimization strategy	Optimization goal	Main findings
Denton et al., 2007	Operational level	Stochastic, heuristics	Minimize cost	Heuristic to sequence surgeons in order of increasing DOS variance and use of stochastic modelling to hedge against uncertain DOS times improves OR utilization.
Hans et al., 2008	Tactical level Operational level	Heuristics, Monte Carlo simulation	Minimize overtime	Clustering surgeries with a similar DOS and variability leads to reduced overtime and slack compared to base surgical plans generated by specialists.
Adan et al., 2009	Tactical level	MIP, stochastic	Minimize OR, ICU and ward bed overutilization and underutilization	Using MIP, can generate improved master surgical schedules by considering a stochastic LOS.
Lamiri et al., 2009	Operational level	Monte Carlo simulation, MIP, multiple heuristics	Minimize cost and overtime	Compared multiple optimization techniques. Combination of Monte Carlo simulation and MIP performed best and with least data.
Fei et al., 2009	Tactical level	Heuristics	Maximize OR utilization, minimize cost	Using a column-generation-based heuristic, cases are assigned to optimized ORs for the week, using an open scheduling strategy.
Cardoen et al., 2009	Tactical level Operational level	MIP	Maximize bed utilization	To determine the amount of OR time assigned to surgeons for outpatient surgery.
Marques et al., 2012	Operational level	Integer linear programming	Maximize OR utilization	Improvement in total OR utilization with reduction in length of surgical wait lists.
Lehtonen et al., 2013	Operational level	Discrete-event simulation	Maximize OR utilization	Improved DOS categorization and higher levels of schedule granularity (30 min vs 60 min) improve utilization.
M’Hallah et al., 2014	Operational level	Discrete-event simulation	Maximize OR utilization, minimize overtime	Cases grouped by mean DOS and OR utilization simulated. Recommends transfer of the last case in a busy room to a free one, group patient waitlists, and reduce workload by 10% or cancel last cases if planned overtime in schedule.
Van Huele et al., 2014	Tactical level Operational level	MIP	Minimize overtime	Evaluated the effect of certain surgeon constraints (surgeon availability, number of OR days/week, and consecutive surgeon hours and days) on performance of elective OR schedule.
Astaraky et al., 2015	Operational level	Heuristics, stochastic, Markov decision process	Minimize patient wait, overtime, and ward capacity	Improved surgical planning using combined model with stochastics over heuristics alone. Provides different schedules depending on hospital resource availability.
Baesler et al., 2015	Operational level	Heuristics, discrete-event simulation	Minimize total OR time	Account for surgery-grouping-specific preoperative, postoperative, setup, and recovery times. Combined heuristics with simulation to search for an optimal schedule.
Silva et al., 2015	Operational level	Heuristics, integer linear programming	Maximize OR utilization	Assign surgeries to maximize the OR utilization while matching surgeries to anaesthetist skills.
Wang et al., 2015	Operational level	Heuristics	Optimize number of ORs and PACU beds	Schedule patient surgeries based on priority where fixed resources are limited. But optimizes ORs and surgery allocation if flexibile.
Guido et al., 2017	Tactical level	Heuristics	Maximize number of surgeries	Assigns available OR time to surgeons while considering hospital objectives, surgery characteristics.
Zhang et al., 2019	Operational level	Stochastic, Markov decision process	Minimize cost	Combined Markov decision process and stochastic optimization lowered cost, shortened wait time, and improved OR and recovery bed utilization compared to stochastic optimization alone.
Bai et al., 2022	Operational level	Heuristic	Minimize OR idle time	Model can reduce total OR time while meeting resource (personnel and hospital) constraints. Connected stages of preop, OR, and recovery optimization.

ICU, intensive care unit; MIP, mixed integer programming; PACU, postoperative anesthesia care unit.