…The facemask has been used in surgical settings for over a hundred years; first described in 1897, at its inception, it consisted merely of a single layer of gauze to cover the mouth, and its primary function was to protect the patient from contamination and surgical site infection. This practice was substantiated, at the time, by a recent discovery which demonstrated that bacteria could be disseminated from the nose and mouth during normal conversation as observed by bacterial colony growth on strategically placed agar plates in theatres. In the 1940s and 1950s, antibiotics and aseptic technique came to the forefront of infection control strategies within the surgical setting. Until recently, it has remained unclear as to whether bacterial colony growth on an agar plate was a direct correlate of surgical site infections and also whether the purpose of the surgical mask has been superseded by more modern strategies of infection control.
In order to advocate the validity of an intervention in medicine, it must satisfy three levels of evidence: efficacy, effectiveness and cost-effectiveness. In the context of facemask, efficacy is whether masks prevent the propagation of droplets derived from the mouth and nose of the operating staff. Effectiveness is whether efficacy translates into a significant reduction in surgical site infection morbidity and mortality. And finally, cost-effectiveness determines whether the cost-to-benefit ratio of this effect would be desirable compared to an alternative course of action.
Intuition would suggest that facemasks offer a physical barrier preventing the emanation of droplets from the oral or nasal passages and therefore satisfy the efficacy requirement of the evidence ladder. However, there are a number of different hypotheses as to why this may not be the case. ‘Venting’ is a phenomenon whereby air leaks at the interface between mask and face which can act to disperse potential contaminants originating from the pharynx. The accumulation of moisture, during prolonged usage, may exacerbate this problem by increasing resistance to air flow through the filter itself. Moisture accumulation is also thought to facilitate the movement of contaminants through the material of the mask itself by capillary action. These bacteria can subsequently be dislodged by movement. Friction at the face/mask interface has also been demonstrated to disperse skin scales which can further contribute towards wound contamination.
In the modern era, there has also been a scarcity of experimental evidence to support the effectiveness of facemasks in the prevention of surgical site infections. The earliest retrospective studies failed to demonstrate any statistically significant improvement in surgical site infection rates following the use of masks. Indeed, the latest National Institute for Health and Care Excellence guidelines on the matter do not require operating staff to wear a mask in theatre. This decision was based primarily upon the findings of a Cochrane systematic review. This review was guided by the findings of two particular randomised/quasi-randomised control trials. The latest update of this review, which was amended after the publication of current National Institute for Health and Care Excellence guidelines, included one further study.
…Overall, we found very few studies and identified no new trials for this latest update. We analysed a total of 2106 participants from the three studies we found. All three studies showed that wearing a face mask during surgery neither increases nor decreases the number of wound infections occurring after surgery. We conclude that there is no clear evidence that wearing disposable face masks affects the likelihood of wound infections developing after surgery.
…More research in this field is needed before making further conclusions about the use of face masks in surgery.
see also:
https://www.isitzen.com/blog/2021/3/cochrane-mask-studies
