A novel coronavirus was first encountered in Wuhan, Hubei Province, China, in December 2019 when patients started to present with community acquired pneumonia. 1 As a result of global travel the virus was rapidly disseminated to all provinces of China and 25 countries in Asia-Pacific region, North America, Europe, and South America within one month of its discovery. 2 Emergency of International Concern (PHEIC). 3 The UK's emergency response to the COVID-19 pandemic thereafter stems from protocols that were developed both during and after the Severe Acute Respiratory Syndrome (SARS) epidemic of 2003. However major differences exist between SARS and COVID-19 in that the former was considerably more dangerous with a cumulative fatality rate (CFR) of 11% compared to an estimated CFR for COVID-19 of <1%. 4, 5 Aerosol-generating procedures (AGPs) are prevalent in head and neck surgery and it is likely that practice will have to change as a result of the COVID-19 pandemic at least in the short term. On 27 March 2020 Public Health England published updated guidance on personal protective equipment (PPE) suggesting the need to limit the use of fluid resistant surgical facemasks (FRSM) to non-AGP procedures and FFP2/FFP3 for AGPs. 6 Given that sources of PPE are variable and may remain so in the future we sought to review the literature to investigate whether any additional lessons could be transposed from either the SARS or early COVID-19 experience into head and neck surgery to aid healthcare workers in both the outpatient and operating theatre environments.
We carried out a literature review over the past two decades amongst Ovid (Medline) and Scopus (Elsevier) along with the Cochrane databases with an English language restriction.
The topics thought most worthy of consideration related to high-volume suction/aspiration and pre-procedural mouth washing. Given that many of these topics are also pertinent to the practice of dentistry search terms included 'dentistry', 'dental' and 'dental care'. Abstracts were evaluated and full-text articles obtained as relevant.
A small number of studies fulfilled the search criteria in relation to high-volume suction/aspiration. Jacks designed a study to compare the concentration of airborne particulates using different methods of evacuation generated airborne particulates from a 25,000 cps magnetostrictive ultrasonic scaling instrument in a laboratory setting. 7 second in-vitro study used an ultrasonic scaler to generate an erythrosin dye solution aerosol at 17.5 ml/min with a high-volume evacuator being used to assess the reduction in contamination within a plastic enclosure containing a 1 cm grid laid out on 4 slides. 8 The number of squares containing a red erythrosine spot were counted and considered to represent J o u r n a l P r e -p r o o f aerosol contamination. The high-volume evacuator attachment produced a 93% reduction in the number of contaminated squares (chi squared significant at P < 0.05). In the only in-vivo study 30 subjects had half their mouths cleaned using an ultrasonic scaler as a control and the other half using high-volume suction. 9 Four culture plates were placed on the operator and patient with high-volume suction resulting in an 81% reduction in mean bacterial culture forming units (CFUs).
The use of pre-procedural mouthwashes in reducing bacterial contamination is well established. [10] [11] [12] There is some evidence that similar mouthwashes might demonstrate 
Aerosols are defined as airborne particles that range in size from 0.5 to 10 microns. They are universally produced during instrumentation of the upper aerodigestive tract but can be reduced. Irrigant solutions, which produce the therapeutic effects of lavage, also combine with blood, saliva, and bacteria to produce potentially harmful airborne particulates.
Saliva contains a high viral load in COVID-19 with up to 1·2×10 8 infective copies/mL. 16 PCR assay techniques have demonstrated that the nasopharynx appears to have a higher viral load than the oropharynx suggesting that reduction of nasal viral titres may be of at least as much importance as the oral cavity/oropharynx. 17 Viral load in sputum from the lower respiratory tract is also of importance with the suggestion that viral shedding is high during the early phase of illness and more prominent in the upper compared with the lower respiratory tract. 18, 19 High-volume suction draws a large volume of air away from the oral and nasal environment during operative procedures and in so doing reduces the amount of aerosol. Whilst intra-oral suction devices such as those employed in dental surgeries are not universally present within Topical PVP-I usage is well tolerated, inexpensive and, for a patient about to undergo a procedure, a one-off episode. However, healthcare workers may choose to adopt PVP-I use over a more regular and sustained period. Daily use of 5% PVP-I mouthwash over a sixmonth period does not appear to influence thyroid hormone levels (serum T3/T4 and free T4) and although a small increase in TSH levels may result the latter remains within the normal range. 20 In a study looking at the excretion of iodine in healthy subjects, average ingestion of J o u r n a l P r e -p r o o f majority of iodine being cleared by the kidneys. The WHO recommended daily allowance of iodine for an adult is 0·15 mg. PVP-I 10% contains an equivalent of 11 mg/mL of iodine suggesting that with daily use 4 mg of iodine would be delivered per day to staff depending on the method of application. Since aerosolised secretions from the lower respiratory tract almost certainly also have a part to play in disease transmission such an approach clearly only forms one part of a strategy to reduce transmission as an adjunct to other elements of personal protective equipment. The suggestion that tempering Chlorhexidine rinses (47ºC vs 18ºC) may reduce bacterial aerosol contamination further is untried with viral load. 12 A recent systematic review and rapid review of surgical masks versus FFP3 masks found no statistical difference in effectiveness between the masks regarding influenza like viral infections. 22, 23 The filtration capacity of a standard surgical face mask is highly variable compared to an FFP2 or FFP3 mask. Oberg and co-workers concluded that none of the surgical masks tested in-vivo on 40 subjects exhibited adequate filter performance and facial fit characteristics to be considered respiratory protection devices. 24 The mean penetration by 0.8μm latex spheres was 37.89 (95% CI: 25.8% to 50.0%).
In the dental surgery high-volume aspiration can be supplemented by a physical barrier (e.g. rubber dam) and in such an environment there may be no significant additional benefit in wearing an FFP3/FFP2 over a surgical mask. There is a much larger difference if the quality of the HFHVE is reduced or where, in procedures such as head and neck surgery, a physical barrier is impractical. High-volume suction reduces bioaerosols by between 81% to 90%.
Manufacturers suggest that fluid resistant surgical facemasks filter 62% of airborne particles compared with 94% for FFP2 masks and 99% for FFP3 masks. Given the lower suction efficiency of hospital-based suction equipment compared to that available in dental practices it is possible to estimate an overall reduction in AGPs with routine hospital suction use of J o u r n a l P r e -p r o o f 92.8% for the surgical mask, 98.9% for FFP2 masks and 99.8% for FFP3 masks respectively with a risk difference of 7.03 between the surgical mask and FFP3 and a relative risk of 0.929.
These results are hypothetical and due to the lack of specific studies of virus penetration of facemasks are based on surrogate and composite outcomes. There is an urgent need for more specific studies to address these issues in the clinical environment.
The authors have no financial, personal, political, or academic interests to declare in relation to the content of this study.
No conflict of interest J o u r n a l P r e -p r o o f