The study is based on nearly 66,000 adults who underwent six common surgical procedures, and is considered among the most thorough investigations to date on this issue.

“This study strengthens the evidence that overlapping surgery is a reasonable practice for many cases,” wrote the authors, who included Eric Sun, MD, PhD, an assistant professor of anesthesiology, pain and preoperative medicine at Stanford University School of Medicine in California, and Anupam B. Jena, MD, PhD, in the Department of Health Care Policy, Harvard Medical School in Boston.

Despite the safety finding, subset analyses indicated some patients face a greater risk for harm if their surgeon is participating in an overlapping surgery. These patients are in the highest quintile for preoperative predicted risk for death and complications, based on age and preexisting medical conditions. They experienced higher rates of mortality and increased complications during overlapping procedures than patients whose surgeon was not involved in an overlapping surgery. Patients undergoing CABG also had small increases in death and complications during overlapping surgeries.

Investigators focused on six subspecialty surgical procedures: total knee or hip arthroplasty; lumbar, thoracic or cervical spine surgeries; CABG; and craniotomy. These operations were selected because the incidence of overlapping surgery is thought to be high. The study did not look at overlapping surgery for any general surgery procedures.

Using data from the Multicenter Perioperative Outcomes Group, an electronic health record registry of all surgical and diagnostic procedures requiring anesthesia care from more than 50 hospitals, investigators examined the effect of overlapping surgery in nearly 66,000 adults at eight American medical centers between 2010 and 2018. In all, nearly 12% of the cases studied had some overlap with another case.

A case was defined as overlapping if the surgery start and end times overlapped with one other operation of any type performed by the same surgeon for at least 60 minutes. For cases less than 60 minutes in duration, overlap was defined as having a start and end time that overlapped with the entirety of the other case.

In contrast, in exploratory subgroup analyses, in-hospital mortality rose to 4.0% from 2.2% for CABG surgery performed as overlapping procedures compared with the nonoverlapping approach. Postoperative complications from CABG also increased in overlapping procedures, up to 34.5% from 30.2% in nonoverlapping. Furthermore, in high-risk patients, surgical overlapping was associated with significantly increased mortality (5.8% vs. 4.7%) and complication rates (29.2% vs. 27%).

In an accompanying note, JAMA deputy editor Edward H. Livingston, MD, said the study answers an important, unresolved question: “Is surgery safe as practiced in academic environments that balance the needs of safe patient care with those required to train the next generation of surgeons? The answer appears to be yes.”

He added that the risks associated with concurrent surgery—in which the attending surgeon is not present during a part of the operation considered critical—remain unknown and are not addressed by this study. There is not yet a precise definition of the critical components of an operation that require the presence of an attending surgeon, he noted. “That definition should be determined by an independent body of clinicians familiar with the operating room environment and monitoring to ensure that the attending surgeon is in the operating room during that time.”

David Soybel, MD, the division chief for general surgery specialties and surgical oncology at Penn State Hershey College of Medicine, in Hershey, said the practice may be safe for most patients but the ethical justification is not clear. “Studies like this one tell us that for certain types of cases, under certain circumstances, overlapping surgery doesn’t seem to be unsafe. … But flip that around and ask, ‘In what way would a patient benefit from this?’ I think it’s a really good conversation to have, even though it makes people a little uncomfortable to talk about it.”

He believes there is only one scenario in which patients benefit from overlapping surgery: when the practice makes it possible for a patient to undergo surgery at an earlier date by a uniquely qualified surgeon. “Otherwise I don’t see how or why a patient would ever be that accepting of the idea that their surgeon was out of the room and had planned to be out of the room.”

Dr. Soybel cited several unanswered questions about overlapping surgery: What should be disclosed to the patient, and how should that be done? What is the standard of care when a surgeon is not in the room? What factors other than the surgeon affect outcomes during overlapping surgery?

The ACS does not currently plan to update its guidelines since the study confirms earlier evidence that overlapping surgery is a safe practice, said David Hoyt, the executive director of the ACS, in an interview.

He reiterated that the patient should be informed if there’s going to be a period of time when the surgeon is moving between two rooms. “You can do it very generally, but the important thing is that you have some way to communicate that to the patient.”

In this study, the overlapping approach increased the duration of surgery by about 30 minutes, from 173 to 204 minutes. The additional time may result from parts of the operation being performed by junior team members, or delays associated with waiting for the surgeon to complete the critical portions of the case, the authors said.

The mean number of cases per surgeon was 320, with a median of 199. Of the 207 surgeons in the analyzed sample, 73% performed overlapping procedures. Overlapping scheduling was most common for craniotomy and least common for total knee arthroplasty.