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Healthcare Economics, Policy, and Organization: Original Clinical Research Report

US National Anesthesia Workload on Saturday and Sunday Mornings

Dexter, Franklin MD, PhD*; Epstein, Richard H. MD; Campos, Javier MD; Dutton, Richard P. MD, MBA§

Author Information
doi: 10.1213/ANE.0000000000001447
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Organizations contemplating the addition of elective (scheduled) surgery on Saturdays have few scientific data to aid in that decision.a For example, it is unknown to what extent elective schedules on Saturdays are used (ie, can be contributing to reducing queues for operating room [OR] anesthesia). Previous publications comprise 2 case series: 1 for inguinal herniorrhaphy1 and 1 for elective orthopedic cases.2 In the current paper, we analyze data3 from the American Society of Anesthesiologist’s Anesthesia Quality Institute (AQI) to estimate what percentage of the anesthesia workload in the US represents scheduled cases on Saturdays during typical work hours (7:00 am to 2:59 pm).


The University of Iowa Institutional Review Board “determined” that this work “is not human subjects research.”

The AQI data analyzed were from all US anesthesia groups that submitted cases to the National Anesthesia Clinical Outcomes Registry (NACOR) for all 12 months of 2013.4 The N = 2,075,188 cases were transmitted monthly by participating anesthesia practices, as described previously.5 See Figure 1 of our recently published article for details; groups needed to provide cases with start and end of anesthesia times including date and time zone, surgical Current Procedural Terminology code, and type of anesthesia.4 For each of the cases, data extracted were the date and time of the start of billed anesthesia care, duration of anesthesia care, whether or not general anesthesia was administered, facility, and Clinical Classifications Software (CCS) categorization of primary surgical procedure based on the Current Procedural Terminology (CPT®) code.b The case time data were predominantly anesthesia times from electronic billing records, values that are audited heavily by primary payers (eg, the Centers for Medicare and Medicaid Services), because the duration of care is a substantial component of professional fees. Anesthetics with a primary Current Procedural Terminology of labor epidural and/or cesarean delivery were excluded (eg, 59,400 and 59,510).

Figure 1.
Figure 1.:
Percentage of total US anesthesia time performed 7:00 am to 2:59 pm of each day of the week. The N = 13 four-week periods were used to calculate the standard errors of the mean, showed by the error bars. The error bars are present (Saturdays and Sundays) but are so small that they hardly appear. The figure shows the 72.8% ± 0.4% of the US total anesthesia operating room workload that was performed 7:00 am to 2:59 pm. The Saturday bar displayed equals 1.57% ± 0.03%, and the Sunday bar equals 1.19% ± 0.02%. The difference of these 2 means is 0.38%. From the results, the mean of the difference between Saturday and Sunday equals 0.38% ± 0.02%. Thus, the figure shows that the mean difference of the percentages between Saturday and Sunday is very small (0.38%) because each of the 2 component percentages themselves are small (ie, there is much less surgery on weekends than Mondays to Fridays).

We summed total minutes of anesthesia time nationwide for 5 eight-hour periods: Saturdays, 7:00 am to 2:59 pm; Sundays, 7:00 am to 2:59 pm; Saturdays, 8:00 am to 3:59 pm; Sundays, 8:00 am to 3:59 pm; and Mondays to Fridays, 7:00 am to 2:59 pm. Local time zones were used.4 Batches of 13 four-week periods were created for each of the 5 intervals, as well as the total anesthesia minutes for the 4-week period (ie, any day of the week and time of the day). The primary endpoint for each 4-week period was the difference in the anesthesia minutes between the Saturday and the Sunday, 7:00 am to 2:59 pm, normalized by the total minutes for the period. Because urgent and emergent cases6–9,c present randomly,d and elective scheduling on Sundays is rare, we considered the difference between the hours of Saturday minus Sunday cases to represent elective case scheduling.e Student 1-group 1-sided t test was used to calculate standard errors (N = 13).11–18 Student 1-group 2-sided t test was used to compare the proportion to 1.0% (planned a priori) and 0.5%.

We also performed multiple sensitivity analysis to assess the potential impact on conclusions of our selected primary end point. We repeated calculations using 8:00 am to 3:59 pm. We limited consideration to general anesthetics. We compared the anesthesia minutes Saturday 7:00 am to 2:59 pm and those weekdays 3:00 pm to 10:59 pm. Finally, we summarized results by the CCS category and by the studied facility (N = 656). The cases are from self-reported medium-sized (100–500 beds) community hospitals (36.7% of minutes; 27.9% of facilities), unlisted (missing value; 21.6%; 21.2%), University hospitals (14.3%; 2.7%), large community hospital (>500 beds; 13.5%; 4.4%), freestanding surgery centers (6.3%; 23.8%), small (<100 beds) community hospitals (3.3%; 4.7%), attached surgery centers (2.8%; 8.5%), specialty hospitals (1.4%; 4.0%), and offices (0.2%; 2.7%).


The difference in the anesthesia minutes between Saturdays and Sundays, 7:00 am to 2:59 pm (ie, elective cases), represented just 0.38% ± 0.02% of the total minutes nationwide. The P < 0.00001 compared with 1.0% and, also, with 0.5%; the upper 99% confidence interval was 0.42% (N = 13 four-week periods, each with ≥499 facilities performing ≥139,501 anesthetics).

Findings for general anesthesia alone were the same (0.38% ± 0.02%), in part, because general anesthesia was used for 71.6% ± 0.4% of anesthesia minutes on the Saturday mornings. Results were insensitive to the specific time, being 0.39% ± 0.02% for 8:00 am to 3:59 pm. The absolute percentage difference was small between Saturday and Sunday because the absolute percentages were small for the weekends (Figure 1). Saturdays from 7:00 am to 2:59 pm had 7.5% ± 0.2% of the average anesthesia minutes of a Monday through Friday 3:00 pm to 10:59 pm interval. Among the 190 different CCS categories of procedures performed on weekends, the 5 categories accounting for the greatest differences between Saturdays and Sundays contributed 20.9% ± 1.4% of the minutes: colonoscopy and biopsyf; cholecystectomy and common duct exploration; upper gastrointestinal endoscopy; “other vascular catheterization, not heart”; and “anesthesia” (ie, surgical codes not provided to AQI by the anesthesia group). Among the 656 different facilities, 345 performed cases on weekends; the 5 facilities accounting for the greatest differences between Saturdays and Sundays contributed 19.1% ± 1.3% of the minutes: 3 reported being large, 1 university, and 1 unlisted.


Before the availability of NACOR data, information on US national anesthesia workload was limited. For example, to understand the pharmacoeconomics of medications with faster time from end of surgery until extubation, we examined when cases were performed at a single university hospital, Thomas Jefferson University.19 Less than 2.5% ± 0.1% of cases were performed on weekends, and this was despite there being some elective cases scheduled on Saturdays.19 Using NACOR data, the nationwide percentage of total anesthetic minutes performed on weekends was 5.2% ± 0.1%.4 That percentage is similar to that found in the 1996 French national survey: “5% and 2% of anesthetics were conducted on Saturdays and Sundays, respectively.”20 At large hospitals, such weekend workloads are sufficiently great that there is often >1 case performed simultaneously, and so operational research methods were developed to increase productivity while not increasing patient and surgeon waiting.8,10,21–26 However, such methods did not provide insight into the quantitative contribution of elective (scheduled) cases on the Saturdays. In the current report, we show that, although a few anesthesia groups likely are performing elective (scheduled) cases on Saturdays, such cases contribute negligibly (<0.5%) to the total national anesthesia workload. The conclusions are robust statistically (ie, P < 0.0001 relative to 0.5%, P < 0.000001 relative to 1.0%). Furthermore, the estimated percentages likely are overestimates of the actual elective workloads for 2 reasons. The percentages would include cases postponed from Friday to Saturday.c Also, NACOR is an American Society of Anesthesiologist’s database; anesthesiologists are more likely to work in large and university hospitals than nurse anesthetists27; and such hospitals accounted for the greatest differences between Saturday and Sunday.

Our results for “Saturday” are based on the traditional US (and European) weekend, with some elective cases scheduled on Saturdays, but not Sundays. Adjustments would need to be made for countries where weekends comprise different days of the week (eg, Israel and Saudi Arabia).

US facilities have tended to add additional OR(s) when the sum of the hours of cases and turnovers per OR per workday is nearly 8 hours.28–30 Scheduling cases for the total workload in each OR to be <8 hours has the benefit of reducing patient and surgeon waiting on the day of surgery.31–34 Shorter durations of the workday effectively provide what many patients want31: morning surgical start times to facilitate outpatient and short-stay procedures3,32–35 that provide the most predictable experience for patients and surgeons. This is the strategy followed in practice. Half (53.0% ± 0.6%) of the US national OR workload is completed slightly after 12 noon (local time) of regular workdays.4 Thus, even though many hospitals have nearly every anesthetizing location in use >8 hours daily, most facilities nationwide (62.3% ± 1.9%, P < .0001) complete most of their weekly anesthesia minutes by noon of regular workdays, Mondays through Fridays.4

Opportunities to reduce health care costs include greater use of fixed (capital) costs (eg, >$1 million per OR for capital and equipment).g Doing so by performing cases on Saturdays rather than on late afternoons has the advantage of reducing the hours that anesthesiologists and nurses work late.36 Furthermore, at the vast majority of hospitals with Sunday night percentage occupancies consistently <95%,c,9 Saturday surgery for cases with postoperative length of stays of no >2 nights can increase surgical production at hospitals constrained by beds. However, there are limitations to implementing Saturday schedules (see footnote a). First, for university hospitals, surgical residents have work-hour restrictions that may prevent them from participating in elective weekend cases.37–39 Second, patient outcomes for cases performed on weekends may be worse than if performed on weekdays. Among hospitals in Australia, the risk-adjusted odds of dying within 48 hours after surgery was greater (1.19) for surgery on weekends than on regular workdays.40 Among hospitals in England, the risk-adjusted odds of death within 30 days were greater (1.82) for surgery on weekends rather than on Mondays.41 Among hospitals in the United States, the risk-adjusted odds of in-hospital death was greater for both elective (3.18) and urgent (2.11) surgeries on weekends rather than on weekdays.42 From the NACOR data, nationwide in the United States, surgery starting weekdays after 4:00 pm had greater adjusted odds (1.64) for mortality within 48 hours.43 In contrast, in a single (very large) hospital study, the Cleveland Clinic found no such difference in their complication rates.29,44 In part because of limited reporting of covariates to NACOR, the reason for heterogeneity of findings is unclear, and the extent to which these findings should influence decision making about elective surgery on Saturdays also is unclear. Major adverse events have low absolute rates for many ambulatory procedures (eg, patients undergoing inguinal herniorrhaphy had no reported differences in complication rates when surgery was on a Saturday, P = .75).1 The most common categories of procedures that we identified nationally being performed on Saturdays were such low-risk cases (eg, colonoscopyf). That knowledge could be obtained by using NACOR because it included not just inpatient surgery at hospitals (ie, like the Nationwide Inpatient Sample), care of the elderly (eg, like US Medicare data), or major surgical procedures (eg, the National Surgical Quality Improvement Project). Our results provide organizations with little or no Saturday elective workload, but limited ORs, with the insight that they are the norm (ie, effectively the USA “consensus” is overwhelmingly instead for anesthetics to be completed using relatively long Monday to Friday workdays).36

Table 1.
Table 1.:
Example of a US University Hospital’s Aborted Initiative for Saturday Elective Schedule Predating the Prior Knowledge of the Current Study

Based on the prior knowledge provided by our results, we do not recommend empirical attempts at implementation (Table 1). We recommend that institutions considering Saturday elective surgery perform a thorough statistical analysis of their local workload prior to implementation.12,28 Local calculations of such workload and an analysis of the impact of such an initiative is a potential informatics contribution to hospital administrators that could be offered by anesthesiologists working within a Perioperative Surgical home.h Such OR scheduling analyses result in net cost reduction45,46 and thus can contribute to the Perioperative Surgical Home’s “triple aim” of reducing costs, advancing outcomes, and improving the patient experience.47 Calculations tend to be used for decisions when performed as part of an evidence-based agreement between the anesthesia group and hospital (eg, institutional support).26 Although many anesthesiologists consider cost reduction to be a hospital responsibility, because of the agreement and scientific expertise, implementation is dependent on knowledgeable anesthesiologist medical directors.26,45,48 Use of anesthesia information management system data for managerial decision making is an increasingly important component of anesthesiologists’ workload.49


Name: Franklin Dexter, MD, PhD.

Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.

Conflicts of Interest: The Division of Management Consulting performs some of the analyses described in this paper. Franklin Dexter receives no funds personally other than his salary and allowable expense reimbursements from the University of Iowa and has tenure with no incentive program. He and his family have no financial holdings in any company related to his work, other than indirectly through mutual funds for retirement. Income from the Division’s consulting work is used to fund Division research.

Name: Richard H. Epstein, MD.

Contribution: This author helped analyze the data and write the manuscript.

Conflicts of Interest: Richard H. Epstein declares no conflicts of interest.

Name: Javier Campos, MD.

Contribution: This author helped write the manuscript.

Conflicts of Interest: Javier Campos declares no conflicts of interest.

Name: Richard P. Dutton, MD, MBA.

Contribution: This author helped design the study and write the manuscript and is the archival author.

Conflicts of Interest: Richard P. Dutton declares no conflicts of interest.

This manuscript was handled by: Kate Leslie, MBBS, MD.


aPubMed search on January 18, 2016: (Saturday[TIAB] OR Sunday[TIAB] OR weekend[TIAB]) AND (elective[TIAB] OR schedule[TIAB] OR scheduled[TIAB] OR scheduling[TIAB] OR staffing[TIAB]) AND (operative[TIAB] OR operating[TIAB] OR theatre[TIAB]). The 35 articles included 2 papers related to Saturday elective schedules.1,2

b Accessed June 6, 2015.

cA functional classification is that cases are emergent if they cannot wait safely for a team to come from home, elective if they can wait through the weekend without clinical or economic consequence (ie, patient is outpatient preoperatively), and urgent otherwise.6–8 Because hospitals’ occupancies are greater Wednesdays to Fridays than on Saturdays, and greater or the same between Saturdays and Sundays (ie, greater or equivalent opportunity on Saturdays for urgent surgery to care for patients inpatient preoperatively), we will overestimate the percentage of hours that are “elective.” (, accessed March 14, 2016.)9

dTo estimate emergent workload, we used 1:00 to 4:59 am each day of the week. Overall, the 4 hours accounted for 0.11% ± 0.003% of anesthesia minutes. The Saturday minus Sunday difference was 0.01% ± 0.003%. This may contribute to our overestimating the Saturday elective workload by approximately 0.01%.

eWhether a case was scheduled at least a day ahead is not known accurately for much of the AQI data.10 Thus, such information could not be used for the calculations.

fLawton S. Saturday colonoscopies. The benefits of performing screenings on weekends. Outpatient Surgery Magazine 2016;17:18–19.

g Accessed November 27, 2014.

hAmerican Society of Anesthesiologists. Perioperative Surgical Home. Available at: Accessed January 24, 2016.


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