Patient Safety Tip of the Week

March 12, 2019   Update on Overlapping Surgery



Our regular readers know we are not fans of overlapping surgery. Nevertheless, we always try to present all sides of any controversial issue. In our December 19, 2017 Patient Safety Tip of the Week “More on Overlapping Surgery” we noted at least 8 retrospective cohort studies supporting the safety of overlapping surgery and a single one noting an increased risk of complications with overlapping surgery. Since our last column on the topic, there have been several more studies concluding that overlapping surgery is not associated with increased mortality or morbidity.


The most recent study was just published in JAMA (Sun 2019). Sun and colleagues did a retrospective cohort study of over 66,000 surgeries at 8 centers. They found that, for adults undergoing common operations, overlapping surgery was not significantly associated with differences in in-hospital mortality or postoperative complication rates. As seen in multiple other studies, overlapping surgery was associated with significantly longer case duration.


The study used administrative data and included adults undergoing total knee or hip arthroplasty, spine surgery, coronary artery bypass graft (CABG) surgery, and craniotomy. Overlapping surgery was defined as ≥2 operations performed by the same surgeon in which ≥1 hour of 1 case, or the entire case for those <1 hour, occurs when another procedure is being performed.


In addition to in-hospital mortality, the major complications assessed included thromboembolic events, pneumonia, sepsis, stroke, or myocardial infarction and the minor complications included urinary tract or surgical site infection. Data were adjusted for confounders.


In-hospital mortality was 1.9% in overlapping cases vs 1.6% in nonoverlapping cases (difference non-significant). Complications occurred in 12.8% of overlapping cases vs 11.8% of nonoverlapping cases (also a non-significant difference).


However, overlapping surgery was significantly associated with increased mortality and increased complications in 2 pre-specified subgroups. Among patients having a high preoperative predicted risk for mortality and complications, overlapping surgery was significantly associated with increased mortality and increased complications compared with low-risk patients (mortality 5.8% vs 4.7% and complications 29.2% vs 27.0%). Similarly, for patients undergoing CABG, in-hospital mortality rates were significantly higher for the overlapping surgery group (4.0% versus 2.2%) and complication rates were also significantly higher in the overlapping surgery group (34.5% versus 30.2%).


Overlapping surgery was associated with a significant increased surgery length (average 204 vs 173 minutes). That is consistent with multiple other studies, which generally show overlapping surgery cases to be about a half hour longer than non-overlapping cases. That’s always been somewhat of an enigma for us because previous studies on surgical case duration have shown higher rates of infection as case duration increases. We often cite the statistic that infection rates increase by 2.5% for every half hour of surgery (Procter 2010). One previous Canadian study (Ravi 2017) on hip fracture patients and patients undergoing total hip replacement did find a higher rate of infectious complications in those undergoing overlapping surgery. After matching, overlapping hip fracture procedures had a statistically significant greater risk for a complication (hazard ratio 1.85), as did overlapping THA procedures (hazard ratio 1.79). Moreover, for the overlapping hip fracture operations, increasing duration of operative overlap was associated with increasing risk for complications (adjusted odds ratio, 1.07 per 10-minute increase in overlap). For hip fracture patients the complications in the overlapping group were primarily infections and revisions.


We suspect the lack of more infectious complications in the Sun study and most of the other studies may reflect that most of the excess duration in overlapping cases is related simply to wound closure (the prior studies assessed total surgical length without breaking down individual components contributing to duration).


Nevertheless, the longer case duration of overlapping surgery should catch the interest of those interested in optimizing OR efficiency.


Ponce et al (Ponce 2018) analyzed over 26,000 cases done over a 2-year period at a large tertiary academic center by surgeons who performed at least 10% of their cases as overlapping cases. Overlapping procedure patients had an average case length of 2.18 hours compared with 1.64 hours among non-overlapping patients (P < 0.0001), a decreased risk of mortality (RR 0.42), a decreased risk of readmission (RR 0.92), and a decreased risk of experiencing any patient safety indicator (RR 0.67).


Hyder et al. (Hyder 2018) compared their experience with overlapping surgery vs. non-overlapping surgery on pediatric patients at a single children’s hospital. They used various methods to match patients in the non-overlapping cases to those in the overlapping cases. They found no significant difference in mortality between the two groups nor significant differences in length of stay (LOS). They do note that, because mortality rates were very low, that mortality may not be a good parameter to assess. Rather, LOS or intraoperative measures may be more appropriate.


Orthopedics is probably the area in which overlapping surgery is most often practiced. There have been several studies comparing orthopedic procedures done in overlapping vs. non-overlapping fashion. Goldfarb et al. (Goldfarb 2018) looked at over 22,000 orthopedic cases performed in a single ambulatory surgery center, 23% of which were overlapping. Complications were logged into a database monthly by surgeons. The median duration of surgery overlap was 8 minutes. After propensity score weighting, there were only minor differences between groups in operative time, anesthesia time, and tourniquet time and no significant differences in surgical site infection, noninfectious surgical complications, hospitalization, or morbidity.


Dy et al. (Dy 2018) looked at all inpatient orthopedic surgical procedures performed at 5 academic institutions over a one year period. Overlapping surgery was defined as 2 skin incisions open simultaneously for 1 surgeon. There were 14,135 cases, with overlapping surgery in 40%. The frequencies of perioperative complications were 1% in the overlapping surgery group and 2% in the non-overlapping surgery group. There was no difference in mortality and the overlapping group had reduced odds of perioperative complications (OR, 0.61), a lower chance of all-cause 30-day readmission (OR, 0.67), and shorter length of stay.



So, there are now multiple retrospective cohort studies supporting the safety of overlapping surgery and very few noting an increased risk of complications with overlapping surgery.


But, here’s the rub. As we’ve pointed out before, there are 2 basic problem with interpretation of all these studies. First, untoward events related to overlapping surgery, particularly serious ones, are not common. In fact, the vast majority of overlapping surgeries are accomplished without any problems. The serious events therefore get “buried” or “diluted out” in any large series. In fact, the bigger the series, the less likely we are to identify cases in which the overlap contributed to an adverse outcome. Given that a randomized controlled trial is not likely to ever take place, the only real way to determine whether overlapping surgery caused or contributed to such events is to perform root cause analysis of all cases with adverse events, a time- and resource-intensive process.


A second problem is that, even in those studies that used propensity score adjustments to minimize bias, there is likely an element of selection bias. There is really no way from administrative data or even chart review to fully understand why non-overlapping surgery was chosen over overlapping surgery or vice versa. It is quite likely that surgeons may avoid overlapping surgery in patients they consider to be at more risk. Note that the subgroup analysis in the Sun study does indicate that complications may be more common with overlapping surgery in more complex cases. So, when we see a retrospective cohort study that says patients undergoing overlapping surgery do better than those with non-overlapping surgery, we are not at all surprised. If they are less at risk, they should have fewer complications.


We’ll also speculate there might be an element of publication bias as well. Most of the studies come from venues in which the practice of overlapping surgery has been well ingrained.


Those of us involved in patient safety have all seen instances in which overlapping surgery was a contributing factor to or root cause of an adverse event. And just because the population-based studies seem to show a relative safety of overlapping surgery, it does not mean we don’t need to pay attention to the dangers. Wrong-site surgery and retained surgical items are also relatively rare events. Yet we strive to prevent all such cases of those. Why should events related to overlapping surgery be treated differently?


The one thing that is reassuring from these studies is that, with the exception of the Ontario study, there does not seem to be an increased rate of surgical site infections in cases of overlapping surgery. That is somewhat surprising to us, given that virtually all the studies have shown that procedure durations are longer in overlapping surgery. We’ve actually done several columns on prolonged surgical duration and you’ve heard us often use the statistic that infection rates increase by 2.5% for every half hour of surgery (Procter 2010). Many of the above studies showed mean surgical durations on the order of 30 minutes longer in overlapping cases. Thus, we would have predicted we’d see increased infection rates in such cases. But note that those are mean durations. Quite likely there are many cases with prolonged durations of, say, 10 minutes and then other cases with more prolonged durations that raise the mean. Perhaps the latter ones are associated with increased infection rates. That cannot be determined from the currently published studies. It is interesting that in the Canadian study the complication rate did increase incrementally as the duration of overlap increased.


We hope you will go back to our December 19, 2017 Patient Safety Tip of the Week “More on Overlapping Surgery” to see our detailed comments on the following considerations for overlapping surgery:

·       The “Critical Part of the Surgery”

·       Timeouts

·       Post-Procedure Debriefing

·       The Pre-op “Huddle”

·       Duration of surgery

·       Other Infection Control Issues

·       Definition of “Immediately Available”

·       Multitasking

·       The educational/training mandate

·       The Ethical Issue(s)

·       Who Should Be Allowed to Perform Overlapping Surgery?

·       Monitoring Overlapping Surgery


In our December 19, 2017 Patient Safety Tip of the Week “More on Overlapping Surgery” we noted that views of overlapping surgery are largely in the eye of the beholder. We noted studies showing the perception of overlapping surgery differed between surgeons and patients. Another recent pediatric study (Choe 2018) found a significant mismatch between parents' expectations and those of pediatric surgeons about the role of the surgeon on the day of operation, with parents consistently expecting more direct involvement by the attending surgeon.



We hope that you’ll heed the concerns and recommendations from today’s column and our previous columns listed below. If your organization does allow overlapping surgery, we hope you’ll use our “Overlapping Surgery Checklist” to help guide you in planning for safe implementation.



See our previous columns on double-booked, concurrent, or overlapping surgery:


And our “Overlapping Surgery Checklist






Sun E, Mello MM, Rishel CA, et al. Association of Overlapping Surgery With Perioperative Outcomes. JAMA 2019; 321(8): 762-772



Procter LD, Davenport DL, Bernard AC, Zwischenberger JB. General Surgical Operative Duration Is Associated with Increased Risk-Adjusted Infectious Complication Rates and Length of Hospital Stay, Journal of the Amercican College of Surgeons 2010; 210: 60-65



Ravi B, Pincus D, Wasserstein D, et al. Association of Overlapping Surgery With Increased Risk for Complications Following Hip SurgeryA Population-Based, Matched Cohort Study. JAMA Intern Med 2017;  Published online December 4, 2017



Ponce BA, Wills BW, Hudson PW, et al. Outcomes With Overlapping Surgery at a Large Academic Medical Center. Annals of Surgery 2018; Publish Ahead of Print - February 1, 2018



Hyder JA, Hanson KT, Storlie CB, et al. Assessing the Safety of Overlapping Surgery at a Children's Hospital. Annals of Surgery 2018; Publish Ahead of Print – January 25, 2018



Goldfarb CA, Rizzo MG, Rogalski BL, et al. Complications Following Overlapping Orthopaedic Procedures at an Ambulatory Surgery Center. The Journal Of Bone And Joint Surgery 2018; 100(24): 2118-2124



Dy CJ, Osei DA, Maak TG, et al. Safety Of Overlapping Inpatient Orthopaedic Surgery. The Journal Of Bone And Joint Surgery 2018; 100(22): 1902-1911



Choe JK, Ibarra C, Feinn RS, et al. Concurrent Surgery and the Role of the Pediatric Attending Surgeon: Comparing Parents' and Surgeons' Expectations. J Amer Coll Surg 2018; 226(6): 1022-1029



Our own “Overlapping Surgery Checklist”.






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