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FFP3, FFP2, N95, surgical masks and respirators: what should we be wearing for ophthalmic surgery in the COVID-19 pandemic?
Elective surgery has been delayed until the current crisis has settled and in most affected countries ophthalmic surgeons are now performing only emergency or urgent surgery. Vitreoretinal surgery in particular, however, still carries on due to the numerous conditions we treat which are time critical. Recently, it has been recommended by the Royal College of Ophthalmologists (RCOphth) and the British and Eire Association of Vitreoretinal Surgeons (BEAVRS) that we use filtering face-piece (FFP)3 masks during vitrectomy surgery in all patients, in addition to eye protection related to the potential for aerosol production . This has been backed by the American Society of Retinal Specialists (ASRS). Whilst much is still unknown regarding transmission of the SARS-CoV-2 coronavirus, it is interesting to review some of the factors behind this recommendation.
Standard disposable surgical face masks have been the rule in most of our theatres for years. Their function has thought to be two-way but primarily to prevent the passage of germs from the surgeon’s nose and mouth into the patient’s wound. The evidence in terms of reducing infection rates is surprisingly unclear; however, with COVID-19, we are perhaps more concerned with transmission to the surgeon .
Current data suggest person-to-person transmission most commonly happens during close exposure to a person infected with SARS-CoV-2. It is important to remember that recent studies have shown that people with COVID-19 frequently do not report typical symptoms such as fever or respiratory symptoms, and go through a pre-symptomatic phase of several days when they are infectious. Infection is thought to occur primarily via respiratory droplets produced when the infected person speaks, coughs, or sneezes. Droplets can land in the mouths, noses, or eyes of people who are nearby or possibly be inhaled into the lungs of those within close proximity. It is thought that airborne transmission over long distances is unlikely, but the contribution of small particles in aerosols is currently uncertain.
An aerosol (abbreviation of “aero-solution”) in the context of COVID-19 is a suspension of fine liquiddroplets in air. Although well known to occur with coughing and sneezing, they can also be produced during talking and normal breathing .
Respiratory produced aerosol droplets are believed to be generated primarily in the lungs during inhalation, via a “fluid film burst” mechanism in which aerosol particles are produced as a result of the clearance of fluid closures formed in the bronchioles following exhalation. Similarly, laryngeal droplet generation is also believed to occur during speaking because of fluid films bursting when the vocal folds adduct and vibrate within the larynx or during coughing and sneezing due to shear stress in the mucus-air interface within the trachea.
Comparison of FFP2, KN95, and N95 Filtering Facepiece Respirator
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FFR performance standards:
• N95 (United States NIOSH-42CFR84)
• FFP2 (Europe EN 149-2001)
• KN95 (China GB2626-2006)
• P2 (Australia/New Zealand AS/NZA 1716:2012)
• Korea 1st class (Korea KMOEL - 2017-64)
• DS2 (Japan JMHLW-Notification 214, 2018)
• PFF2 (ABNT/NBR 13.698-2011 – Brazil)
As shown in the following summary table, respirators certified as meeting these standards can be expected to function very
similarly to one another, based on the performance requirements stated in the standards and confirmed during conformity
One notable comparison point is the flow rates specified by these standards for the inhalation and exhalation resistance tests.
Inhalation resistance testing flow rates range from 40 to 160L/min. Exhalation resistance testing flow rates range from 30 to
95 L/min. Some countries require testing to be performed at multiple flow rates, others at only the high or low end of those ranges. Although this appears to suggest that the standards’ requirements for breathing resistance (also called “pressure drop”) differ from each other, it’s important to understand that pressure drop across any filter will naturally be higher at higher flow rates and lower at lower flow rates. Given typical pressure curves for respirator filters, the standards’ various pressure drop requirements are actually quite similar. This chart shows a representative filter pressure drop curve. If one filter is tested at a high flow rate, the pressure drop performance will be relatively high. If that same filter is tested at a low flow rate, the pressure drop performance will be relatively low.