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Economics, Education, and Policy: Research Report

Anesthesia Workload Nationally During Regular Workdays and Weekends

Dexter, Franklin MD, PhD*; Dutton, Richard P. MD, MBA; Kordylewski, Hubert PhD; Epstein, Richard H. MD, CPHIMS

Author Information
doi: 10.1213/ANE.0000000000000773
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In this article, we analyze data1 from the American Society of Anesthesiologist’s (ASA) Anesthesia Quality Institute (AQI) to report the U.S. anesthesia workload by time of day and day of the week. The percentages of anesthetizing locations with >8 hours of cases differ among facilities nationally2–4 and among services and days of the week at individual facilities.5 The extent to which first case starts, rather than durations of workdays and weekend cases, drive the number of anesthesia providers nationally is unknown.6 Understanding the determinants of perioperative efficiency nationwide is important. Opportunities to reduce health care costs include greater use of fixed (capital) costs (e.g., >$1 million per operating room [OR] for capital and equipment).a The Triple-R model for transforming ambulatory surgical care includes expanded facility hours to 18 hours per day 7 days per week.b


The University of Iowa IRB determined that this work is not human subjects research.

The AQI data were from all U.S. anesthesia groups that submitted cases to the National Anesthesia Clinical Outcomes Registry (NACOR) for all 12 months of 2013 (Fig. 1). The n = 2,075,188 cases’ times were compared using Central Time (i.e., the time zone of the headquarters of the ASA and AQI)c for use in our companion paper of a call center providing real-time support to anesthesia providers nationwide.7 Anesthesia workload was measured as the time from the start to the end of continuous anesthesia care for each case (i.e., turnover times and delays were not included).

Figure 1
Figure 1:
Anesthesia Quality Institute data analyzed. The cases in its NACOR data warehouse are transmitted by participating anesthesia practices in monthly summary reports. For each of the cases, we extracted the local date and time of the start of billed anesthesia care, duration of anesthesia care, whether general anesthesia was administered, and the local time zone. The case time data are predominantly from electronic billing records, heavily audited by primary payers (e.g., the Centers for Medicare and Medicaid Services). Anesthetics with a primary Current Procedural Terminology (CPT) of labor epidural and/or cesarean delivery were excluded (e.g., 59400 and 59510). NACOR = National Anesthesia Clinical Outcomes Registry.

Days with atypically low workloads nationally (e.g., holidays) were identified by using the counts of general anesthetics nationwide on each Monday through Friday.8 The date at the 5th percentile was a U.S. federal holiday. Thus, dates with caseloads of the ≤5th percentile were treated as holidays.8

We summed minutes of anesthesia time nationwide on regular workdays from 7:30 AM to 3:30 PM in the local time zones. Batches of 13 four-week periods were created for each hour interval (Fig. 2). The percentage of minutes for each period that was from 7:30 AM to 3:30 PM regular workdays was calculated. Student’s one-group 1-sided t test was used to calculate SEs (n = 13).9–16 Because the briefest anesthesia workday (in terms of times of direct patient care) may at some facilities start sooner than 7:30 AM (e.g., 7:00 AM), sensitivity analyses considered other intervals (Table 1). Sensitivity analyses limited analyses to general anesthetics. Sensitivity analyses tested whether few (<10%) minutes of anesthesia time nationwide occurred on weekends.17

Table 1
Table 1:
National Findings for Anesthetic Minutes Using Anesthesia Quality Institute Data
Figure 2
Figure 2:
General anesthetic minutes nationwide using Anesthesia Quality Institute data in local time zones. The red bars show the percentage of minutes during each 1 hour of regular (non-holiday) workdays. For example, the red bar to the far right shows that 2.7% ± 0.1% (mean ± SEM) of the general anesthesia minutes nationwide over the week were both on regular workdays and between 5:30 PM and 6:29 PM. The red bar third from the right shows that 5.2% ± 0.1% were between 3:30 PM and 4:29 PM. All SEMs were <0.1% and therefore were not plotted. The monotonic decline in red bars after 8:30 AM is consistent with nationwide absence of gaps of cases in the middle of the workday. The blue dots show the cumulative percentage of all weekly general anesthetic minutes. For example, among all general anesthetics nationwide in 2013, 48.6% ± 0.6% of the anesthesia minutes were both on regular workdays and between 7:30 AM and 12:29 PM. For example, 84.1% ± 0.8% of the minutes were both on regular workdays and between 7:30 AM and 6:29 PM. All SEMs were ≤0.8% and therefore were not plotted. The ratios of blue dots can be used to show the percentage of the general anesthetic minutes performed on regular workdays and during ranges of intervals. For example, although it took 11 hours on regular workdays to complete 84.1% ± 0.8% of the weekly minutes, nearly half those minutes (46.9% ± 0.2%) were completed by 11:29 AM (i.e., within 4 hours) and more than two-thirds (68.1% ± 0.3%) were completed by 1:29 PM (i.e., within 6 hours). Many facilities (e.g., outpatient surgery centers) have clinical workdays substantially <11 hours.

We also performed analyses by studied facility (n = 656). For each, we calculated the total annual number of minutes and the total number of those minutes in the mornings of regular workdays (i.e., before 12 noon local time zone). The summary statistic for each facility was whether the minutes in the mornings of regular workdays ≥50% of the facility’s total. By using the method of Blyth-Still-Casella, we calculated an exact CI on the percentage of facilities having most of its minutes of cases over the year in the mornings of regular workdays (StatXact-9, Cytel Inc., Cambridge, MA). The 2-sided binomial test compared the percentage to half (i.e., “most”) facilities. Sensitivity analyses limited analyses to general anesthetics. In addition, sensitivity analyses limited analyses to the n = 45 facilities reported as University and large community hospitals. The cases are from self-reported medium-sized (100–500 beds) community hospitals (34.8% of cases; 25.3% of facilities), unlisted (missing value) (27.5%; 30.0%), freestanding surgery centers (9.1%; 20.3%), University hospitals (8.3%; 2.3%), attached surgery centers (4.7%; 7.2%), small (<100 beds) community hospitals (4.1%; 3.9%), specialty hospitals (1.6%; 3.5%), and offices (0.4%; 2.7%).


Half (53.0% ± 0.6%) of the ASA AQI–reported weekly anesthesia workload was completed by 1:00 PM, local time, on regular workdays. The busiest 8-hour interval was from 7:30 AM to 3:30 PM, and it accounted for 70.3% ± 0.7% of anesthetic minutes (Table 1 and Fig. 2). That 7:30 AM to 3:30 PM interval (using local times) accounted for 74.2% ± 0.7% of the workload on regular workdays. The corresponding interval relevant to staffing of national call centers (6:30 AM to 6:30 PM Central Time) accounted for 82.2% ± 0.7% of anesthetic minutes (Fig. 3). Less than 10% of anesthetic minutes occurred on weekends (P < 0.0001, 5.2% ± 0.1%).

Figure 3
Figure 3:
Anesthetic minutes nationwide using Anesthesia Quality Institute data in the Central Time zone. See Figure 2 for explanation. The axes match Figure 2 for comparison. Unlike Figure 2, all cases are included, not just general anesthesia, and a single time zone is used, as relevant to a national call center.7

Although most facilities completed the majority of their weekly anesthesia workload in the mornings of regular workdays (P < 0.0001, 62.3%, 58.6%–66.1%), just 24.4% of the University and large community hospitals did so (P = 0.0008 relative to half; 13.8%–38.4%).


Slightly more than half of the U.S. national OR workload is completed slightly after noon of regular workdays. Anesthesia providers providing direct OR clinical care 5 days per week from 7:30 AM to 3:30 PM would result in an average time of 11:30 AM (i.e., by noon). Thus, the results likely indicate longer workdays than previous analyses of 2004 and 2006 Medical Group Management Association data.6,d

Even though many hospitals have nearly every anesthetizing location in use >8 hours daily, most facilities nationwide complete most of their weekly anesthesia minutes by noon of regular workdays. Thus, the results match the tendency of U.S. facilities to open additional OR(s) when the sum of the hours of cases and turnovers per OR per workday is nearly 8 hours.18–20 Opportunity for greater use of the capital (building and equipment) probably would involve the use of additional anesthesia providers representing a second shift or use of weekends. However, scheduling cases <8 hours has the benefit of reducing patient and surgeon waiting on the day of surgery,21–24 although such limitation in scheduled hours of surgery does not reduce complication rates or mortality.19,25 Rather than the traditional full day in a large hospital caring for surgical inpatients having major procedures, shorter hours may provide what many patients want21: morning surgical start times to facilitate outpatient and short-stay procedures1,22–24,26 that provide the most predictable experience for patients and surgeons.

Our results were limited to the study of cases and minutes of OR anesthesia, as needed for our companion paper exploring the timing of activity at a national call center.7 Planning remote expert “knowledge consultation”27 for guiding medical decisions depends on the timing of calls during the week, as provided by Figure 3. Such consultation can be, for example, to support telemedicine services to anesthesia providers facing unfamiliar clinical scenarios such as managing rare diseases.7 The cases and minutes of OR anesthesia do not reveal other activities, clinical (e.g., obstetrics, critical care, and acute and chronic pain medicine), non-clinical (management, education, and research),28 and availability for clinical work.8 For example, although 5.2% ± 0.1% of minutes of care were performed on weekends, anesthesia providers needed to be scheduled to be available during these 28.6% minutes of calendar time (i.e., 2 of 7 days).


Name: Franklin Dexter, MD, PhD.

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

Attestation: Franklin Dexter has approved the final manuscript.

Name: Richard P. Dutton, MD, MBA.

Contribution: This author helped conduct the study and prepare the manuscript and is the archival author.

Attestation: Richard P. Dutton approved the final manuscript.

Name: Hubert Kordylewski, PhD.

Contribution: This author helped conduct the study.

Attestation: Hubert Kordylewski has approved the final manuscript.

Name: Richard H. Epstein, MD, CPHIMS.

Contribution: This author helped conduct the study and write the manuscript.

Attestation: Richard H. Epstein has approved the final manuscript.

RECUSE NOTEDr. Franklin Dexter is the Statistical Editor and Section Editor for Economics, Education, and Policy for Anesthesia & Analgesia. This manuscript was handled by Dr. Steven L. Shafer, Editor-in-Chief, and Dr. Dexter was not involved in any way with the editorial process or decision.


a Accessed November 27, 2014.
Cited Here

b Feryal Erhun, Wednesday, November 12, 2014, WC40 INFORMS 2014 Meeting in San Francisco, CA. Available at: Accessed November 27, 2014.
Cited Here

c The times in the AQI database were stored in the local time zone. They were converted to Central Time based on the zip code of the location of the case and the date of the start of the case. We used Central Time, as a matter of convenience, because the geographic center of population of the U.S. is Central Time. The American Society of Anesthesiologists and AQI are in Chicago, Illinois, which follows Central Time. The Central Time zone is Coordinated Universal Time (UTC) minus 6 hours during Standard Time and minus 5 hours during Daylight Savings Time. Available at:,, and Accessed April 1, 2014.
Cited Here

d Abouleish A, Evenson TB. The fallacy of the field of dreams business plan: a downward trend in anesthesiology productivity. ASA Newslett 2007;71:30–2.
Cited Here


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© 2015 International Anesthesia Research Society