key: cord-0836695-r4gsuq36 authors: Liu, D. C. Y.; Koo, T. H.; Wong, J. K. K.; Wong, Y. H.; Fung, K. S. C.; Chan, Y.; Lim, H. S. title: Adapting re‐usable elastomeric respirators to utilise anaesthesia circuit filters using a 3D‐printed adaptor ‐ a potential alternative to address N95 shortages during the COVID‐19 pandemic date: 2020-05-26 journal: Anaesthesia DOI: 10.1111/anae.15108 sha: 3792eb2f8bec7fb7ced97ea6db0ce7dbabe84819 doc_id: 836695 cord_uid: r4gsuq36 The COVID‐19 pandemic has increased the demand for disposable N95 respirators. Re‐usable elastomeric respirators may provide a suitable alternative. Proprietary elastomeric respirator filters may become depleted as demand increases. An alternative may be the virus/bacterial filters used in anaesthesia circuits, if they can be adequately fitted onto the elastomeric respirators. In addition, many re‐usable elastomeric respirators do not filter exhaled breaths. If used for sterile procedures, this would also require modification. We designed a 3D‐printed adaptor that permits elastomeric respirators to interface with anaesthesia circuit filters and created a simple modification to divert exhaled breaths through the filter. We conducted a feasibility study evaluating the performance of our modified elastomeric respirators. A convenience sample of eight volunteers was recruited. Quantitative fit testing, respiratory rate and end‐tidal carbon dioxide were recorded during fit testing exercises and after 1 h of wear. All eight volunteers obtained excellent quantitative fit testing throughout the trial. The mean (SD) end‐tidal carbon dioxide was 4.5 (0.5) kPa and 4.6 (0.4) kPa at baseline and after 1 h of wear (p = 0.148). The mean (SD) respiratory rate was 17 (4) breaths.min(−1) and 17 (3) breaths.min(−1) at baseline and after 1 h of wear (p = 0.435). Four out of eight subjects self‐reported discomfort; two reported facial pressure, one reported exhalation resistance and one reported transient dizziness on exertion. Re‐usable elastomeric respirators to utilise anaesthesia circuit filters through a 3D‐printed adaptor may be a potential alternative to disposable N95 respirators during the COVID‐19 pandemic. The COVID-19 pandemic has caused a worldwide surge in the consumption of personal protective equipment including disposable N95 or equivalent respirators. These respirators are recommended when performing aerosol generating procedures including tracheal intubation and extubation [1, 2] . For anaesthetists who perform aerosol generating procedures, the critical shortage of these respirators is a pressing issue. National Institute for Occupational Safety and Health (NIOSH)-approved elastomeric respirators may be suitable alternatives when used with compatible NIOSH or European Certification (CE)-approved filters such as P100 and P3 [1, 3] . Healthcare personnel can be rapidly fit tested and trained to use them [4] . During the COVID-19 pandemic, the supply of elastomeric respirator filters may also be depleted. In addition, many re-usable elastomeric respirators do not filter exhaled breaths [1] , but simply have an expiratory oneway valve. Therefore, elastomeric respirators also require modification when respiratory protection from the user to the patient is also required (e.g. sterile procedures). High-efficiency filters routinely used in anaesthesia circuits are designed to filter viruses and bacteria [5] . There are two types of filters; electrostatic and mechanical (also known as pleated hydrophobic). Advantages of electrostatic filters include: low resistance; light weight; small size; and low cost. Disadvantages of electrostatic filters include lower filtration efficiency and vulnerability to liquids (and any microbe contained in the liquid) [5] . Mechanical filters generally have higher filtration efficiency compared with electrostatic filters and are more resistant to liquids. Disadvantages of mechanical filters include higher resistance, heavier weight, larger size and higher cost [6] . Applications of 3D printing in the field of anaesthesia have included: creating airway models for pre-operative planning [7, 8] ; producing airway stents [9, 10] ; facial prosthetics [11] ; and creating spinal column [12] and bronchial tree [13, 14] education models. Facing the shortage of oxygen delivery devices and personal protective equipment in the COVID-19 pandemic, 3D printing has been used to convert snorkel masks into CPAP masks for patients [15] and full-face respirators for healthcare workers [16, 17] . Venturi valves [18] and ventilator splitting devices [19] are also being tested and produced. In this feasibility study, we designed a 3D-printed adaptor that allowed 3M TM (St Paul, MN, USA) elastomeric respirators to interface with anaesthesia circuit filters and made a simple modification to the elastomeric respirators to divert exhaled breaths through the filter as well. Fit testing of respirators used during aerosol generating procedures is required. Therefore, it seems reasonable to use both qualitative and quantitative fit testing to evaluate the performance and safety of elastomeric respirators that have undergone the modifications we propose. Ethics Committee, we recruited eight volunteers who provided their written informed consent. As this was a feasibility study with no comparator group, no power calculation was performed. Primary outcomes were quantitative and qualitative fit testing. Secondary outcomes were end-tidal carbon dioxide, respiratory rate and volunteer self-reporting of discomfort. Due to their widespread use and availability, we chose to design a 3D-printed adaptor for the 3M 7501 (small) and printer (Utrecht, Netherlands) using polylactic acid (Premium PLA, Formfutura BV, Nijmegen, Netherlands). Printing instructions and a web link to the stereolithography files for the adaptor and cap can be found in online Appendix S1. Polylactic acid was chosen as it is biodegradable, non-toxic and has a long history of being used for food storage [21] and medical implants [22] . Two configurations were tested. Configuration 1 consisted of inhalation through a single anaesthesia circuit filter and exhalation through the elastomeric respirator exhalation valve (Fig. 1b) . [23] . The fit factor is a ratio of these concentrations. A fit factor in the range of 1 to 200+ is calculated with ≥ 100 constituting a pass [24] . Being the most commonly available anaesthesia circuit filter in our department, we tested the Undis BVF-02 [25] (Shaoxing, Zhejiang, China) electrostatic filter (without a heat and moisture exchanger). It has a viral and bacterial filtration efficiency of > 99.99%. As most electrostatic filters have a filtration efficiency of < 99% [6] , therefore the PortaCount N95-companion mode was chosen. Quantitative fit testing can be seen in Figure 3 . A 3M 601 fit test adaptor was installed between the elastomeric respirator and the 3D-printed cap. Initial fit testing was determined as satisfactory if no leaks were detected during pressure seal checks and stable fit factors were obtained during the real-time display function on the PortaCount Pro + 8038 tester. The real-time display allows a test subject to experiment with strap tension and other adjustments while watching the effect in real-time [24] . If the initial tests were unsatisfactory, the volunteers were fitted with an alternate sized respirator and retested. Following satisfactory initial fit testing, the volunteers performed full standardised quantitative fit testing [26] . The volunteers performed test exercises consisting including normal breathing; deep breathing; head side to side; head up and down; talking out loud; grimace; and bending with touching toes. Fit testing was performed three times: using configuration 1; using configuration 2; and using configuration 2 after wearing the respirator for 1 h. End-tidal carbon dioxide and respiratory rate were Eight volunteers (five men, three women) completed the study ( Table 1) This study demonstrated that interfacing an anaesthesia circuit filter with re-usable elastomeric respirators may be a feasible alternative to disposable N95 respirators for healthcare providers undertaking aerosol generating procedures in patients with COVID-19 disease. Quantitative fit testing should be mandatory before using re-usable elastomeric respirators as a significant proportion of volunteers failed the real-time fit factor test despite having satisfactory qualitative negative and positive pressure seal checks, in line with published guidelines [3, 26] . Once the four volunteers were refitted with a smaller-sized respirator, quantitative fit testing was excellent for all eight volunteers. Exhalation through the anaesthesia circuit filter was well tolerated with no significant change in end-tidal carbon dioxide or respiratory rate. Given this is a feasibility study with a convenience sample of only eight volunteers, firm conclusions cannot be drawn. Elastomeric respirators are designed to undergo repeated disinfection. The cost to print an adaptor and a cap using the recommended polylactic acid as a material is approximately £3 sterling ($3.73 US, 3.5 Euros). We recommend, should these items be required for use, they should be treated as single-use, disposable items as their integrity and safety after disinfection cannot be guaranteed. Other materials may be suitable for 3D printing the adaptor if they are airtight and biocompatible; however, such use requires communication with regulatory bodies within the country before use as stringent standards must be followed [27] [28] [29] [30] [31] . We sealed the exhalation valve with a piece of plastic in configuration 2 forcing exhalation through the anaesthesia circuit filter. For convenience, we cut a piece of plastic from a zipper storage bag and placed it between the exhalation valve and the head harness assembly (Fig. 2) This study was designed to be a feasibility study with descriptive outcome measures and no power analysis was done beforehand. We chose to test the respirators for 1 h as most aerosol generating procedures can be completed within this timeframe. In conclusion, we have modified a NIOSH-approved elastomeric respirator not intended for medical use to function as an N95 respirator by interfacing with a standard electrostatic anaesthesia circuit filter with and without occluding the built-in expiratory valve. If N95 or equivalent respirators and NIOSH-approved filters become difficult to source, anaesthesia circuit filters when combined with wellfitted NIOSH-approved elastomeric respirators using an interposed 3D-printed connector may be a potential solution. Strategies for optimizing the supply of N95 respirators: COVID-19 COVID-19 personal protective equipment (PPE) Respiratory Protective Equipment at Work, 4th edn. London: Health and Safety Executive Training and fit testing of health care personnel for reusable elastomeric halfmask respirators compared with disposable N95 respirators Heat and moisture exchangers and breathing system filters: their use in anaesthesia and intensive care. 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Part 2 -practical use, including problems, and their use with paediatric patients Medicines and Healthcare products Regulatory Agency. MHRA Guidance on coronavirus Enforcement Policy for Face Masks and Respirators During the Coronavirus Disease (COVID-19) Public Health Emergency (Revised) Health Canada. 3D printing and other manufacturing of personal protective equipment in response to COVID-19 No external funding or competing interests declared. Additional supporting information may be found online via the journal website.Appendix S1. Printing instructions and stereolithography files for the adaptor and cap.