Dissipating The Myth of Shoe Covers

If you work in a hospital chances are you've put on shoes covers. This is a well intentioned practice largely predicated on a misunderstanding about the history of medicine. In order to understand this myth we need to go back to the early days of modern surgery.

The early 20th century was a dynamic time in surgery. The advent of sterile technique, effective anesthesia, and the development of new surgical tools and techniques advanced the field rapidly. Despite these improvements the operating rooms of the early to mid twentieth century posed some unique risks for patients and staff. One complication in particular was greatly feared. In the words of one author, "Death by anesthetic explosion is given heavy emphasis... not only because it is the most dramatic of all surgical fatalities, but also because it is so unusual.” The author went on to recommend that "Conductive shoes should be worn by all hospital personnel.”

The problem was that friction between dissimilar materials led to the accumulation of static electricity, which could not be grounded if the person was wearing non-conductive footwear such as the typical rubber-soled shoes. This static electricity could ignite highly flammable anesthetic gases such as ether. The remedy was simple: specialized conductive shoes (worn with cotton socks while standing on special conducting floors) permitted the accumulated static charge to be dissipated harmlessly.

There was a considerable industry that emerged, and several products were developed promising to mitigate the risk of OR fires due to static electricity. In the words on one inventor: 

"Everyone has experienced electrical shocks after scuffing across a rug, or touching a door handle of a moving car, etc. These sparks are only minor unpleasantries in most instances, but in certain environments they are capable of setting off severe and disastrous explosions. For example, although the problem has had very little publicity and laymen are not generally aware of it, doctors know that the danger of explosion is always present in a surgical operating room because anesthetic gases, such as ether, are highly explosive. The slightest electrical spark can and has caused tragic explosions. Thus, one object of my invention is to promote safety in operating rooms by preventing these sparks from occurring.” [Pence, US Patent 3335506, 1967]

His device is shown below:

Along with specialized conducting shoes, a panoply of other inventions appeared, including charge dissipating floors, beds, clothing, and other devices. Low tech approaches were also advocated, including the practice of placing wet towels around one’s shoes, as illustrated by Thomas et al:

An anesthesiologist illustrates how to use wet towels to dissipate static electricity and prevent operating room fires when using flammable anesthetic gasses. (Thomas, J Natl Med Assoc. 1960)

Fortunately, the flammable anesthetic era passed swiftly. The invention of the triad of halothane (1956), enflurane (1966) and isofluorane (1979) as well intravenous agents such as fentanyl (1960), etomidate (1964), and propofol (1977) effectively ended the use of flammable ethers.

Soon, in an effort to save money, the disposable shoe covers with grounding leads were replaced by non-grounding covers, which can be distinguished based on the absence of the black stripe.

Shoe covers without (left) and with (right) conductive grounding strips.

The explosion hazard now largely extinguished, physicians who remained accustomed to the ritual of donning shoe covers invented an alternative raison d’être for the covers: to protect their shoes from contamination and thereby reduce infection.

This rationale, now long accepted, is untrue. 

In 1991, Humphreys et al demonstrated that the use of overshoes do not in fact prevent surgical site infections. And, indeed, shoe covers may actually increase the risk of infections, as the act of donning or doffing over shoes can actually increase hand contamination. In one study, the hands of 18 volunteers were examined before and after putting on over shoes demonstrated new colonization of the hands with organisms likely obtained from the shoes.

One plausible use for shoe covers is protecting the wearer’s shoes, but even at this they are far from perfect. A study by Weightman and Banfield found that when, over a 5 day period, they collected 1387 discarded single use over-shoes, only 29% were intact when filled with water, and of the 103 with visible blood on them, 32% had blood on the inside. 

So now, decades after the demise of ether, the volatile anesthetic that was the original reason raison d’être for grounding shoe covers, can we finally put this myth to rest? Recently, several professional organizations have advocated for shoes that remain in the surgical areas instead of donning and doffing shoe covers. 

As medicine advances, we must look critically on the rituals we practice. We should retain the practices based on evidence and merit (hand washing), while discarding, like soiled overshoes, the atavistic ones (such as white coats) that recall obsolete dogmas but provide no enduring benefit.