Welcome to the new Outpatient Surgery website! Check out our login FAQs.
Drawing Up a Winning Schedule
How to maximize OR efficiency and minimize patient waiting time on the day of surgery.
Franklin Dexter
Publish Date: October 10, 2007

So long as there are surgeons who arrive late, cases that run long, nurses who call out sick and ruptured abdominal aortic aneurysms that present at 9 a.m., there will be disruptions in your OR schedule. Yes, things don't always go as planned on the day of surgery.

You must schedule add-on cases. Fill gaps in the schedule. Move cases. Assign staff. Prioritize limited resources and personnel. Prepare patients. Sequence urgent cases. You must adjust on the fly, be comfortable with chaos and sometimes manage by the seat of your pants, by instinct or by intuition.

What if you could integrate decision-making on the day of surgery? After reading this article about OR management on the day of surgery, you'll better understand how to decide what cases to postpone, what cases to move and so forth in response to unforeseen changes in the OR schedule. The goal of all of this is to maximize OR efficiency and minimize patient waiting time.

I've drawn up seven scenarios that might take place in an outpatient surgical facility on the day of surgery, and employed scientific decision-making to provide solutions that maximize OR efficiency in each.

The scenarios are based on the following conditions. First, they involve elective cases scheduled well in advance of surgery, without urgent cases or a substantial add-on workload. Second, each case can be done in any of the ORs by any of the nursing and anesthesia staff members. Finally, the eight-hour workday for all ORs begins at 7 a.m. and ends at 3 p.m. Given these conditions, the definitions and statistical methods can be simplified markedly.

Scenario 1:
An admissions nurse calls in sick.
Everyone is hustling, but they've fallen a bit behind schedule. OR 1 and OR 2 both call for their next patients at 11 a.m. Both rooms are expected to be ready within 30 minutes, but realistically, either OR could be delayed an additional 15 minutes. The case in OR 1 is scheduled to begin at noon. OR 1 is running ahead of schedule, but would still have to wait for its patient. OR 2 is running behind schedule by about one hour. While OR 1 is expected to finish its cases by 4 p.m., OR 2's work is expected to conclude at 2 p.m. Which OR should be served first?

Solution: Reducing overutilized OR time - the time an OR is occupied beyond its allocated eight-hour workday - and its associated labor costs should be a higher priority than reducing how long surgeons and patients wait past scheduled start times. Staff members should focus first on readying a patient for OR 1.

Scenario 2:
An anesthesiologist is medically directing CRNAs in two ORs with caseloads of pediatric patients.
For the first cases of the day, both ORs will have mask inductions followed by IV placement. OR 3 has eight 45-minute cases scheduled. OR 4 has two three-hour cases. Each OR has one surgeon doing all of the cases. Both ORs are ready to go. Overutilized OR time is not expected in either. Which of the two ORs should the anesthesiologist start first?

Solution: Since overutilized OR time - the deciding factor in Scenario 1 - is not expected, the decision should be based on reducing the amount of time that patients wait beyond their scheduled start times. If procedures occupy an extra 10 minutes, for instance, OR 3's total patient waiting time would increase to 70 minutes (seven patients multiplied by 10 extra minutes each). OR 4's total waiting time, on the other hand, would be 10 minutes (one patient multiplied by 10 minutes). The anesthesiologist should begin OR 3 first.

Guiding Principles for Efficient Scheduling

 •  Maximize OR efficiency on the day of surgery by minimizing hours of overutilized OR time.

 •  Minimizing waiting times is often a better guide than basing your scheduling paradigm on a first-come, first-served basis. Really, what does it matter how many weeks before the day of surgery that the patients in OR 1 and OR 2 were originally scheduled for surgery? First-scheduled, first-served is sufficient for sequencing urgent cases but not sufficient when combining urgent cases and elective cases, as often occurs in practice.

 •  Decision-making on the day of surgery has a negligible impact on OR efficiency if there are no overutilized hours. The principal determinant of OR efficiency is OR allocation, not actions on the day of surgery. This means having the right number of staff, working the right number of hours, on the right days of the week, for specific surgical services.

 •  When scheduling a list of elective cases in the same OR on the same day, sequence the cases from the most to the least predictable in duration. Generally, shorter cases will be more predictable than longer cases.

- Franklin Dexter, MD, PhD

Scenario 3:
An anesthesiologist is supervising resident physicians in OR 1 and OR 2.
Allocated OR time is from 7 a.m. to 3 p.m. These ORs have just finished their first cases. The last case of the day in OR 1 is scheduled to be finished at 2:30 p.m. The last case of the day in OR 2 is scheduled to be finished at 4:30 p.m. Which OR should the anesthesiologist start next?

Solution: OR 1 is expected to have no overutilized hours. OR 2 is expected to have 1.5 overutilized hours. If the patient for OR 2 is ready, the anesthesiologist should start OR 2 first.

Scenario 4:
When an OR is finished with a case, nurses use an intercom system to notify the housekeeping staff that it is ready for cleaning.
Only one housekeeper is available when the intercom announces, "Done in OR 1." Moments later, the intercom sounds again: "Done in OR 2." If the cases in OR 1 are expected to be done around 3:30 p.m. and those in OR 2 by 1 p.m., which OR should the housekeeper clean first?

Solution: The answer depends on the possibility of overutilized OR time which, as I've explained, is the higher priority. The housekeeper should focus on OR 1 first in order to reduce overutilized OR time.

Scenario 5:
A surgeon is scheduling two cases for an afternoon. There are no medical reasons why one must be performed before the other.
Patient A's procedure is likely to take 45 minutes. Realistically, its duration will not be less than 30 minutes or more than one hour. Patient B's procedure is likely to take two hours and 30 minutes. Its duration may be as little as one hour, 45 minutes, or as long as three hours, 30 minutes. Which patient's procedure should be scheduled first?

Solution: Since one procedure will be done directly following the other, overutilized OR time is not a consideration. Instead, the choice revolves around patients waiting past their scheduled start times. If Patient A's shorter, more predictable case were first, Patient B would have to wait 15 minutes at most. If Patient B's longer, less predictable case were first, Patient A might have to wait as long as one hour. Patient A's case should be performed first.

Decision-making: The Four Priorities

In his article (Dexter F, Epstein RH, Traub RD, Xiao Y. Making management decisions on the day of surgery based on operating room efficiency and patient waiting times. Anesthesiology 2004; 101: 1444-1453), Dr. Dexter and his colleagues report that the day of surgery operational decisions that increase OR efficiency the most follow four ordered priorities.

 •  Maintain patient safety. The first priority is maintaining patient safety. A facility's staff should meet medical deadlines in the event of urgent cases, but must also consider the availability of surgeons, anesthesia providers and nurses who can perform those cases as well as an OR equipped to handle them.

 •  Open access to OR time. The second is providing surgeons with open access to OR time when they and their patients choose. This means a case should only be canceled on the day of surgery if it cannot be done safely (following the first priority).

 •  Maximizing OR efficiency. On the day of surgery, this means minimizing overutilized hours - the time an OR is occupied beyond its allocated workday.

"Maximizing OR efficiency is a lower priority than surgeon open access to OR time," writes Dr. Dexter, "because otherwise no case would be performed that would be expected to result in any overutilized OR time."

As demonstrated in Dr. Dexter's scenarios, you can reduce overutilized hours by judging expected (mean, for example) durations of cases, and scheduling the longest ones first.

 •  Reducing patient waiting time. The fourth and final priority is reducing patient waiting time after a scheduled start time for elective cases. (In urgent cases, the waiting time is considered the time between when a patient is ready and when the case begins.)

In remarks made after the article's publication, Dr. Dexter explains, "Maximizing OR efficiency is a higher priority than reducing patient waiting, because the opposite would result in irrational decisions. Scheduled delays of several hours would be planned between all successive surgeons' series of cases to reduce potential late starts, even if that would result in substantial overutilized OR time every day in every OR."

"Some organizations try to use the scheduling paradigm of first scheduled, first served instead of minimizing waiting times as the fourth ordered priority," the doctors write in the article. In a series of experiments, they show that "it makes no sense to base the decision ' on how many weeks before the day of surgery that [patients] were originally scheduled for surgery. First scheduled, first served is sufficient for sequencing urgent cases but not sufficient when combining urgent cases and elective cases, as often occurs in practice."

- David Bernard

Putting a Price on OR Efficiency

Even though operational decision-making is almost never based on financial criteria (rather, it's based on how to get the existing cases done, making decisions on the day of surgery, scheduling cases, and planning staffing and OR allocations), there is a way to translate OR efficiency into dollars and cents (Strum DP et al. Anesthesiology 1999). See the formula on the blackboard on the left. Here's how a fast anesthesiologist increased OR efficiency by preventing one overutilized hour. As you read along, keep in mind that OR time is a sunk cost on day of surgery. OR nurses and nurse anesthetists are full-time, hourly employees. OR time is allocated for eight hours, from 7 a.m. to 3 p.m. There is estimated to be nine hours of cases. The anesthesiologist gets every IV first stick, A lines and C lines first stick and does a fiberoptic intubation in eight minutes. The OR finishes at 3 p.m.

- Franklin Dexter, MD, PhD

Scenario 6:
A pathology technician and pathologist are on site.
Two ORs have frozen sections for them to review at the same time. While the pathology team will work diligently for both ORs, they have to choose one OR's sections to review first. Excluding pathology delays, OR 3 is expected to finish at 3:45 p.m. and OR 4 at 1 p.m. Which OR should the pathology team assist first?

Solution: The focus should be on reducing overutilized OR time. Even with no delays, OR 3's procedure can be expected to occupy 45 minutes of overutilized time, since the workday ends at 3 p.m. As a result, the pathology team should work on OR 3's specimens first.

Scenario 7:
Only one nurse is currently available to retrieve supplies from the sterile area.
In OR 1, a surgical team is setting up equipment while anesthesia induces the patient. They call for supplies. Moments later, surgery in OR 2 is temporarily halted due to a broken instrument. OR 2's team calls for supplies second, stat, because the surgeon is scrubbed and frustrated.

Excluding the time it takes to fill the requests, OR 1's current case is expected to end at 1 p.m. and OR 2's at 1:45 p.m. OR 1's case started 30 minutes early and the surgeon has one patient to follow. OR 2's case started 25 minutes late; the surgeon has three patients to follow. No overutilized OR time is expected in either room.

Solution: Focusing on OR 2 would reduce the total amount of time patients wait past their scheduled start times, so the nurse in the sterile area should deliver OR 2's supplies first.

Imperfect science
The science of decision-making tends to be highly technical because its objective is not simply to show a rational way to do something. Rather, it is to prove mathematically that one particular way is better than any other.

In December, my colleagues and I published an article in Anesthesiology discussing decision-making on the day of surgery (see "Decision-making: The Four Priorities"). We demonstrated how the scientific methods of decision-making apply comprehensively to OR management's operational issues. Factors such as advance scheduling and sequencing of cases, accounting for delays, and allocating and releasing OR time can all be considered mathematically. The science of decision-making to OR management can't, of course, pacify surgeons' and staff members' frustrations with working later than planned, and there will always be unexpected disruptions and delays in OR caseloads.

However, the scenarios and principles described above may offer a better understanding of how to address the decisions involved in the day-to-day operation of your facility.

Remember, the schedule drives everything that happens in the OR, but the schedule depends on many subsystems such as staffing, the availability of supplies and equipment. A poorly run schedule can lead to bottlenecks, frustrating not only patients and families but physicians, staff and nursing units.

Scheduling Q & A

Question: We are implementing block OR allocation. Any pointers?

Answer: First, nothing is more important financially when implementing or adjusting blocks than calculating the correct allocations. A good summary of a decade of science is to allocate OR time based on OR efficiency, not based on OR utilization. Allocating OR time based on OR utilization is both logically and computationally flawed, and consequently will often give the wrong answer to the problem. If you allocate too much OR time, then much will be underutilized, thereby reducing OR efficiency. If you allocate too little, then much will be overutilized to finish the cases, resulting in even more expensive overutilized hours. The allocations need to be correct to get the right balance.

Question: What is a good OR utilization value for a surgical suite? What's too low or high?

Answer: Sixty percent is absurdly low, and 95 percent is too high. The range is too large to be useful, which is why the answer to the question is that you need to analyze each surgical suite. Almost always when someone is measuring utilization, this is for tactical decision-making. The reason for this is that utilization best applies when one considers ORs as being a fixed resource, not finishing late. From a macro perspective, which is quite suitable from a tactical perspective, that is fine. From an operational perspective, and particularly on the day of surgery, this is quite absurd. Allocating OR time based on OR utilization is both logically and computationally flawed, and consequently will often give the wrong answer to the problem. Instead, you should allocate OR time based on OR efficiency. The latter considers not just underutilized OR time (utilization, for example), but also the higher cost of planning too little OR time resulting in more expensive overutilized OR time. Whereas decision-making based on OR utilization relies first on knowing what utilization is best, there is one single answer to best staffing based on OR efficiency and minimizing staffing costs.

Question: What example shows the difference between allocating OR time based on OR efficiency versus OR utilization?

Answer: Consider a service with total hours of elective cases including turnover times averaging five hours every Monday. The service was allocated a single OR for eight hours. Then, its adjusted utilization is 62 percent. There are three underutilized hours and zero overutilized hours. Because there are no overutilized hours, allocation based on OR efficiency is identical to allocation based on OR utilization. In contrast, suppose that the same surgical suite has three of its eight ORs as unblocked, open, first-come first-served, other time. The surgical suite staffs in eight-, 10- and 13-hour shifts, where 13 hour = 40 hours a week / 3 days per week. Then, those three ORs could be allocated as 8/8/8, 8/8/10, 8/10/10, 10/10/10, 8/8/13, 8/13/13/, 13/13/13, 8/10/13, 10/10/13, and 10/13/13. Only by calculations based on OR efficiency, which considers both expected underutilized and overutilized hours of OR time, can you make a good staffing decision.

- Franklin Dexter, MD, PhD