The results of our analyses support our hypothesis that AEs are influenced by the time of day of surgery. We identified a small but significant increase in AEs in the early morning compared with late morning and early afternoon hours. This effect was robust throughout a number of different analyses and event types. We also identified a significant and sizable increase in AEs in the late afternoon compared with early morning. Post hoc analyses revealed that this effect may have been driven primarily by the most frequent events of PONV and pain management.
In addition to the significant effects of AEs, there was a significant and sizeable increase in administrative delays in the late afternoon. This suggests that there may be a relationship between administrative delays and AEs that requires further investigation.
There are a number of reasons why AEs may occur more often at the end of the day, including (1) end of day fatigue, (2) afternoon circadian lows, (3) care transitions, (4) change in makeup of the care team, (5) changes in case load, (6) physiological changes in the patient, or (7) other unrecognized factors. Some of these same factors might also be relevant as an explanation for the increased AE rate in the early morning.
These data were collected at our medical center where all anesthesia care is supervised by a faculty physician anesthesiologist and delivered primarily by either an anesthesia resident or a CRNA. The attending anesthesiologist may supervise up to four CRNAs or up to two residents in separate operating rooms. The work day generally begins between 6 and 7 am and ends between 3 and 6 pm for most attendings and residents. However, each day several attendings stay later to finish cases or remain on a late call schedule that ends between 6 and 9 pm. Both attendings and residents work a distinct night call schedule. CRNAs work 12 hour shifts of 7 am to 7 pm, 11 am to 11 pm, or 7 pm to 7 am. Scheduling details are visually depicted in fig 5.
Figure 5Approximate Duke University Medical Center anesthesia staff schedules over a 24 hour day. Note: Medium grey areas represent flexible start and stop boundaries as well as times of overlapping coverage and transition.
Because of this scheduling system, times of transition in anesthesia care are most likely to occur around 6–8 am and 3–7 pm. Changes in the makeup of the care team may also occur during these times. In particular, a greater fraction of the case load may be covered by CRNAs rather than by residents during the 3–7 pm time frame. There also may be increases in case load per attending physician associated with the 3–7 pm time frame as supervision transitions to fewer late call anesthesiologists. Our finding of a substantial increase in delays in the late afternoon also suggests a potential problem of workload at this time. In contrast to the 6–8 am time of transition when well rested anesthesiologists arrive to begin the day, physicians supervising cases during the 3–7 pm transition times are usually physicians who are continuing cases, taking over new cases, and who began their work day between 6 and 7 am.
Arbous et al29
identified specific issues associated with both transitions and the makeup of the patient care team that affect postoperative mortality and coma. They found an increased risk of perioperative death associated with intraoperative change of one anesthesiologist by another. In addition, the risk of severe morbidity and mortality was reduced by (1) direct availability of an anesthesiologist (via intercom rather than phone or pager), (2) the presence of a full time (versus part time) anesthetic nurse, and (3) the presence of two individuals at emergence and termination of anesthesia. While there are some relevant differences in the model for anesthesia care in the United States and Europe—for example, differences in training and responsibilities of anesthesia nurses and requirements for anesthesiologists to be present at critical points such as induction and emergence—it is likely that, as case load increases, anesthesiologists may be faced with difficult choices about where their presence is most needed or when they should call for help.
This study has some limitations. Firstly, it is based on non‐anonymous self‐reports. Although the database is used as the official perioperative record which requires providers to be diligent in reporting significant events, they may be biased in how they document events or in their decisions whether or not to report minor incidents. They may be more likely to select QI event labels that describe the event more generally or are seen as patient related events rather than labels that suggest clinician error and indicate a cause or possible blame. There also may be an increase in documentation associated with cases in which there are transitions, either for purposes of providing key information to oncoming providers or for providing a clear historical record of whether events occurred before or after the transition.
Secondly, a reduction of over 30% in our sample size due to missing data calls into question the robustness of the database for the purposes of these analyses. Although we were unable to identify specific causes of missing data, we have no reason to believe that there are any systematic biases associated with missing data that would affect the results of our study.
Lastly, we were unable to clearly determine which events were preventable. This limits our ability to determine whether or not the time of day effects have underlying causes that can be controlled. For example, circadian effects on the patient such as changes in the sensitivity to pain30
or propensity for PONV could partly explain our results.
Most studies on the effects of fatigue on clinical outcomes have focused on sleep deprivation or disrupted circadian rhythms—for example, looking at post call effects15,21
or comparing night time with daytime performance.7,20
We are not aware of any other studies that have revealed decrements in clinical outcome associated with the beginning or end of the work day. This study presents evidence of a significant and sizeable increase in the incidence of anesthetic AEs in the late afternoon hours. It is unclear whether the increase in AEs was due to (1) problems related to increased case load and delays at these times, (2) effects of caregiver fatigue after many hours on the job, (3) problems that occur because of transitions, (4) increased reporting during times of transitions, or (5) other unidentified factors such as changes in the makeup of the anesthesia care team or physiological changes in the patients. Future research should focus on identifying the causes of increases in anesthetic AEs in the late afternoon. After these causes are identified, strategies to reduce or eliminate these events should be evaluated.