The mistakes largely result not from surgeon fatigue, but from the stress arising from emergencies or complications discovered on the operating table, the researchers reported.

The study found that emergency operations are nine times more likely to lead to such mistakes, and operating-room complications requiring a change in procedure are four times more likely.

It also happens more often to fat patients, simply because there is more room inside them to lose equipment, according to the study.

Two-thirds of the mistakes happened even though the equipment was counted before and after the procedure, in keeping with the standard practice.

Most lost objects were sponges, but also included were metal clamps and electrodes. In two cases, 11-inch retractors metal strips were forgotten inside patients. In another operation, four sponges were left inside someone.

The lost objects were usually lodged around the abdomen or hips but sometimes in the chest. They often caused tears, obstructions or infections. Most patients needed additional surgery to remove the object. In other cases, patients were not even aware of the object, and it turned up in later surgery for other problems.

在美国，每年约有1500名病人体内留有糊涂医生做手术时忘记收拾的钳子、纱布及其他工具。

研究人员发现，这些错误的发生大都不是因为手术疲劳，而是手术压力。这些压力主要来自紧急情况或者手术进行中发现的并发症等等。

研究显示，紧急手术中发生这类事故的几率是常规手术的9倍。如果在手术时发现有其他并发症而不得不调整手术程序的话，发生遗留事故的可能性是平常的4倍。

研究还表明，这类情况经常发生在体型肥胖的病人身上，因为在他们体内有更大的空间让医生落下东西。

按照常规，手术前后必须清点医疗工具。然而这类医疗事故中有三分之二是在常规清点工作已经进行的情况下发生的。

落在病人体内的绝大部分是医用纱布，但也不乏金属钳和电极。在两起事故中，医生把长达11英寸的牵开器金属条落在病人体内。而另一例事故中，病人体内一次落下了四块纱布。

这些东西通常是遗失在病人的腹部或臀部，但有时也会在胸部。这些遗留物会引起病人的伤口撕裂、梗塞及感染。大部分病人都需要再做一次手术来取出那些异物，但有时病人根本毫无察觉，体内的东西直到进行其他手术时才被发现。