Harvard School of Public Health researchers have found a new health concern for overweight Americans—having surgical tools lost inside their bodies during surgery.

A study published last week in the New England Journal of Medicine found that surgical teams are 10 percent more likely to accidentally leave surgical tools inside patients if they are overweight.

Corpulent patients are more susceptible to the error simply because there is more room inside them where the tools can be lost, the study found.

Metal clamps and sponges are commonly left inside patients, but retractors and electrodes are also sometimes forgotten.

Two-thirds of the mistakes analyzed by the study occurred even though the equipment was counted before and after the operation, in keeping with standard surgical procedure.  

Is estimated that about 1,500 out of over 28 million operations performed nationwide each year result in instruments being left inside the patient, according to the study.

Although relatively low, the estimated number of cases are too many, healthcare experts say.

“No one in any role would say it’s acceptable,” said Donald Berwick, president of the Boston-based nonprofit Institute for Healthcare Improvement.

Contrary to common belief, the study does not cite surgeon fatigue as a reason for forgetting part of the equipment inside of a patient but explains that the mistakes largely result from the stress arising from emergencies or complications discovered on the operating table.

Risk of retention of a foreign body after surgery is nine times as high in emergency operations and four times as high when unplanned changes in surgical procedure occurs, the researchers observed. But the length of the operation or the hour of day when the operation is performed does not appear to make a difference.

“It tends to be in unpredictable situations,” said lead researcher Dr. Atul A. Gawande of Brigham and Women’s Hospital, which conducted the study with the School of Public Health.

The lost objects are usually lodged around the abdomen or hips, and sometimes in the chest or other cavities.

The unexpected souvenirs often cause tears, obstructions or infections—and, in extreme cases, death.

The study showed that 69 percent of the cases required re-operation to remove the object, but sometimes the object came out by itself.

In other cases, patients were not even aware of the object, and it turned up in later surgery for other complications.