Surgical mask

Source: Wikipedia, the free encyclopedia.
Surgical mask
Surgical face mask.jpg
A surgical mask with hand-tied straps
Other namesProcedure mask, medical mask, isolation mask, laser mask, fluid-resistant masks, face mask

A surgical mask, also known as a medical face mask, is a personal protective equipment worn by health professionals during medical procedures.[1][2] When worn correctly, it prevents airborne transmission of infections between patients and/or treating personnel by blocking the movement of pathogens (primarily bacteria and viruses) shed in respiratory droplets and aerosols from the wearer's mouth and nose.[3][4][5]

Typically quite impermeable to moisture, these masks act as an additional barrier for the airway and are not usually designed (unless N95-rated) to completely prevent the wearer from inhaling smaller airborne pathogens, but some research suggests that they may still be protective by filtering out and trapping most of the droplets that carry pathogens.[6] There is limited evidence that surgical masks protect both the wearer (by filtering the inhaled air) and bystanders (by blocking down forceful exhalations from the wearer that can spread pathogens afar).[7]

Surgical masks were originally designed to protect medical personnel from accidentally breathing or swallowing in splashes or sprays of bodily fluids, and the effectiveness of surgical masks against influenza-like infections has not been confirmed by high-quality randomized controlled trials.[8] Commonly seen surgical masks vary greatly by quality and levels of protection. Despite their name, not all surgical masks are appropriate to be used during surgery. Surgical masks may be labeled as surgical, isolation, dental or medical procedure masks.[9]

Surgical masks are made of a nonwoven fabric created using a melt blowing process. They came into use in the 1960s and largely replaced cloth facemasks in developed countries.[10] The colored (usually dark blue, green, or occasionally yellow) side of the mask (fluid-repellant layer) is to be worn outwards, and the white side (absorbent layer) inwards.[11][12][13] With respect to some infections like influenza surgical masks could be as effective as respirators, such as N95 or FFP masks;[14][15][16] though the latter provide better protection in laboratory experiments due to their material, shape and tight seal.[17][18]

The use of surgical masks during the COVID-19 pandemic was a subject of debate,[19] as mask shortage was a central issue.[20][21] Surgical masks are popularly worn by the general public all year round in East Asian countries like China, Japan and South Korea, especially during allergy and flu seasons, to reduce the chance of spreading airborne diseases to others, and to prevent the breathing in of airborne irritants such as pollens or dust particles created by air pollution (though dust masks are more effective against pollution).[22] Additionally, surgical masks have become a fashion statement, particularly in contemporary East Asian culture bolstered by its popularity in Japanese and Korean pop culture which have a big impact on East Asian youth culture.[23][24]

Function

Spraying of respiratory droplets when sneezing. Surgical masks (when used correctly) can retain most of the aerosols released from the wearer, thus reducing airborne spread of pathogens.[25]
Shadowgraph videos of the outer airflow during a sneeze, comparing an unmasked sneeze with several different method of covering one's mouth and nose[26]

A surgical mask serves as a mechanical barrier that interferes with direct airflow in and out of respiratory orifices (i.e. nose and mouth). Most commonly used surgical masks are designed to only trap respiratory droplets, and therefore do not filter or block fine airborne particles that are smaller than the designed filtration ratings, which may be transmitted by coughs, sneezes, unintentional spitting during talking, or certain aerosol-generating medical procedures (e.g. bronchoscopy, laryngoscopy or dental procedures). Surgical masks also cannot provide complete protection from germs and other contaminants because of the often loose fit between the mask edges and the wearer's face,[27] especially when the mask is worn outright incorrectly (e.g. low with the nose and/or mouth exposed).

A surgical mask is a disposable device that creates a physical barrier between the respiratory tract openings (nose and mouth) of the wearer and potentially pathogenic contaminants in the immediate environment. If worn properly, surgical masks are meant to help blocking out most (if not all) large-particle droplets, splashes, sprays, or splatter that may contain viruses and bacteria, keeping them from entering the wearer's nose and mouth.[27], and conversely ere also effective barriers for retaining large droplets released from the wearer's the mouth and nose.[25] Surgical masks help reduce exposure of the wearer's saliva and respiratory secretions to others[27] that could otherwise travel up to 7.9 metres (26 ft).[28] Surgical mask also remind wearers not to touch their mouth or nose, which could otherwise transfer viruses and bacteria after having touched a contaminated surface.[26]

A surgical mask is not to be confused with a respirator (which is specifically rated for sub-micron particles) and is not certified as such. Surgical masks are not designed to protect the wearer from inhaling airborne bacteria or virus particles and are less effective than respirators, which are designed for this purpose.[25] Collection efficiency of surgical mask filters can range from less than 10% to nearly 90% for different manufacturers’ masks when measured using the test parameters for NIOSH certification. However, a study found that even for surgical masks with "good" filters, 80–100% of subjects failed an OSHA-accepted qualitative fit test, and a quantitative test showed 12–25% leakage.[29]

Modern surgical masks are made from paper or other non-woven material and should be discarded after each use.[30]

Physical form

Physical properties of surgical masks
Parameter Typical unit
Pressure differential, ∆P cm of H2O / cm2
Filtration and exposure %
Liquid penetration resistance mbar
Air permeability ml/s⋅cm2 at 100 Pa
Water vapor permeability g/24 hr⋅cm2
Water repellency grade

The design of the surgical masks depends on the intended usages. Usually, the masks are rectangular-shaped with pleats to allow the wearer to expand and curve the mask so it can better cover all the area from the nose to around the chin. The outward-facing side of the mask are typically colored (usually blue, green or yellow) and made thicker, tougher and water-impermeable. The inner layers of the mask are made of three-ply (three layers) melt-blown polymer (most commonly polypropylene) placed between non-woven fabric.[31] The melt-blown material acts as the filter that stops microbes from penetrating and exiting the mask.[31] Some masks have an attached thin polyethylene faceshield (known as "splash shield") to provide additional spray protection over the eye area.

A different type of masks, known as "duckbill" masks, uses a trapezoid pouch-like design that has significantly shortened side edges — sometimes none at all — to minimize loose gaps that pathogens can leak past. These masks are typically made to the N95/P2 standards, and are commonly used for clinical situations that demand fine particulates protection, such as tuberculosis.

Small strips of foam or thickened fabric are often sewn along the top edge of the mask to help better seal away exhaled water vapors (which can fog up eyewears and faceshields) and soak up excess perspiration dripping from above. Small bendable metal strips are frequently added to the top edge to better fit over the nasal bridge. Occasionally adhesive tapes can also be added to secure the seal and prevent the mask from slipping up and down.

The masks are typically fastened to the head with straps or elastic bands that are attached to the mask's four corners.[32] Straps come in four free-hanging ribbons that are manually tied in two pairs horizontally around the back of the head, and are most frequently used in surgical operations due to the ability to customize the strap length and tension comfortably to the wearer's face shape and head movements. Elastic bands come in a pair of loops that can either be horizontally or vertically attached. Horizontal loops go around the head like tied straps, designed to exert tension on the top and bottom edges of the mask for firmer contact seal, and are usually seen on duckbill masks; while vertical loops hook around the ears with less tension (due to the weaker rigidity of the elastocartilaginous auricles compared to the bony skull) and thus less firmly secured to the face, but are more popular in non-procedural usages due to the ease of putting on and taking off.

Filter material in the middle layer may be made of microfibers with an electrostatic charge; that is, the fibers are electrets. An electret filter increases the chances that smaller particles will veer and hit a fiber, rather than going straight through (electrostatic capture).[33][34][35][better source needed][medical citation needed] While there is some development work on making electret filtering materials that can stand being washed and reused,[36] current commercially produced electret filters are ruined by many forms of disinfection, including washing with soap and water or alcohol, which destroys the electric charge.[37] During the COVID-19 pandemic, public health authorities issued guidelines on how to save, disinfect and reuse electret-filter masks without damaging the filtration efficiency.[38][37] Standard disposible surgical masks are not designed to be washed.

Physical properties and quality

Performance of surgical masks is evaluated based on such parameters as filtration (mask capture of exhaled aerosols), exposure (transfer of aerosols from outside), mask airflow resistance (pressure difference during breathing, ΔP, also known as breathability),[39] liquid penetration resistance, air and water vapor permeability, water repellency (for outer and inner surfaces).[40]

Filtration and exposure is typically measured in bacterial filtration efficiency (BFE) using particles of size 3.0 μm. Particulate filtration efficiency (PFE) using particles of size 0.3 μm is only measured in China.[41]

History

Face masks for use in surgery were developed in Europe by several physicians, including Jan Mikulicz-Radecki at the University of Breslau and Paul Berger in Paris, in the late nineteenth century, as a result of increasing awareness of germ theory and the importance of antiseptic procedures in medicine.[42] In response to a pneumonic plague in Manchuria and Mongolia in 1910, Chinese-Malaysian epidemiologist Dr. Wu Lien-teh greatly improved on the designs he had seen in Europe to develop a face mask of layers of gauze and cotton that would protect both the wearer and others.

Modern surgical masks began to be used in the 1960s. Their adoption caused cloth facemasks, which had been used since the late 19th century, to completely fall out of use in the developed world.[43][44] However, cloth masks and surgical masks both continued to be used in developing countries.[45]

COVID-19 pandemic

As the pandemic raged on, healthcare workers were required to continue wearing surgical masks for 12 or more hours a day. This caused the ear loops of the masks to chafe the back of their ears. Ear savers, plastic straps and hooks that go around wearer's heads, were invented to move the ear loops away from the wearer's ears. They could be made on demand by using 3D printing process.[46]

Use

Healthcare workers

A medical professional wearing a surgical mask during an operation

A surgical mask is intended to be worn by health professionals during surgery and certain health care procedures[47] to catch microorganisms shed in liquid droplets and aerosols from the wearer's mouth and nose.[30] Evidence supports the effectiveness of surgical masks in reducing the risk of infection among other healthcare workers and in the community.[48] However, a Cochrane review found that there is no clear evidence that disposable face masks worn by members of the surgical team would reduce the risk of wound infections after clean surgical procedures.[49]

Healthcare workers are trained in how to put on, handle, remove, and dispose of surgical masks. For healthcare workers, safety guidelines recommend the wearing of a face-fit tested N95 or FFP3 respirator mask instead of a surgical mask in the vicinity of pandemic-flu patients, to reduce the exposure of the wearer to potentially infectious aerosols and airborne liquid droplets.[50][51][52]

General public

A face mask designed for children[53]

In community and home settings, the use of facemasks and respirators generally are not recommended, with other measures preferred such as avoiding close contact, maintaining good hand hygiene,[30] and wearing cloth face coverings.[54]

Surgical masks are popularly worn by the general public all year round in East Asian countries like China, Japan, South Korea and Taiwan to reduce the chance of spreading airborne diseases to others, and to prevent the breathing in of airborne dust particles created by air pollution.[22]

In Japan and Taiwan, it is common to see these masks worn during the flu season, as a show of consideration for others and social responsibility.[55][56][57] Surgical masks provide some protection against the spread of diseases, and improvised masks provide about half as much protection.[58]

More recently, due to the rising issue of smog in South and Southeast Asia, surgical masks and air filtering face masks are now frequently used in major cities in India, Nepal and Thailand when air quality deteriorates to toxic levels.[59][60][61] Additionally, face masks are used in Indonesia, Malaysia and Singapore during the Southeast Asian haze season.[62][63] Air filtering surgical-style masks are quite popular across Asia and as a result, many companies have released masks that not only prevent the breathing in of airborne dust particles but are also fashionable.[64][65]

Additionally, surgical masks have become a fashion statement, particularly in contemporary East Asian culture bolstered by its popularity in Japanese and Korean pop culture which have a big impact on East Asian youth culture.[23][24]

Surgical masks may also be worn to conceal identity. In the United States banks, convenience stores, etc. have banned their use as a result of criminals repeatedly doing so.[citation needed] In the 2019–20 Hong Kong protests, some protestors wore surgical masks amongst other types of mask to avoid recognition, and the government tried to ban such use.[66]

Regulation

Single-use medical masks

In the United States, surgical masks are cleared for marketing by the U.S. Food and Drug Administration. As of 2009, manufacturers of surgical masks must demonstrate that their product is at least as good as a mask already on the market to obtain "clearance" for marketing. Manufacturers may choose from filter tests using a biological organism aerosol, or an aerosol of 0.1 µm latex spheres.[29]

In the European Economic Area (EEA), surgical masks have to be certified through the CE marking process in order to be commercialized. CE marking of surgical masks involves the respect of many obligations indicated in the Medical Device Regulation (Council Regulation 2017/745 of 5 April 2017 concerning medical devices, OJ No L 117/1 of 2017-05-05).

Surgical masks for use in the US and the EEA conform to ASTM F2100 and EN 14683 respectively. In both standards, a mask must have a Bacterial Filtration Efficiency (BFE) of more than 95%, simulated with particles of size 3.0 μm.[67]

In China, two types of masks are common: surgical masks that conform to YY 0469 standard (BFE ≥ 95%, PFE ≥ 30%, splash resistance) and single-use medical masks that conform to YY/T 0969 standard (BFE ≥ 95%).[41][68] Daily protective masks conforming to GB/T 32610 standard[69] is yet another type of masks that can have similar appearance to surgical masks.

See also

References

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External links

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