key: cord-1048387-qusbo9lh authors: Hellman, Samuel; Chen, Grant H.; Irie, Takeshi title: Rapid clearing of aerosol in an intubation box by vacuum filtration date: 2020-06-18 journal: Br J Anaesth DOI: 10.1016/j.bja.2020.06.017 sha: 967cf443158843657334d8f33c5383734d0ae1bc doc_id: 1048387 cord_uid: qusbo9lh nan Editor -Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a highly infectious respiratory pathogen disseminated by droplets and aerosols 1 . Healthcare providers performing aerosol-generating procedures on coronavirus disease 2019 (COVID-19) patients are at risk of infection. Aerosol-generating procedures include but are not limited to tracheal intubation, extubation, mask ventilation, tracheostomy, oropharyngeal/endotracheal aspiration, high-flow air/oxygen delivery, bronchoscopy, esophagogastroduodenoscopy, transoesophageal echocardiography, defibrillation, chest compression, and a range of dental, head and neck, and thoracic surgeries. Variations of Lai's aerosol barrier 2 for limiting healthcare provider exposures has been rapidly adopted, but remains incompletely validated. 3, 3a Cubillos and colleagues 4 reported qualitative results of vacuum filtration, but clinically actionable time-to-clearance information is lacking. Efficacy of particle elimination by vacuum relates to air flow rates, which can be diminished by in-line viral filters essential to decontamination of outflow. Therefore, empirical testing is needed for each vacuum/filter configuration attached to intubation boxes to determine the particle elimination kinetics. Here, we present experimental data on the time course of active aerosol removal, comparing our hospital in-wall suction system and two lowcost commercially-available vacuums using an intubation box. Our two-piece design intubation box ( Figure 1A ) includes active aerosol removal by attaching a vacuum with an in-line high-efficiency viral filter (Draeger SafeStar 55 R , location). Aerosol removal by such filters could mitigate virus dispersion; this filter has 99.9999% viral filtration efficiency. 6 We tested two vacuums, with stated air flow ratings of 60 cubic feet per minute (CFM; Shop-Vac #9303511, manufacturer, location) or 23 CFM (Intex mattress inflator/deflator #66639E, manufacturer, location), attached via standard airway circuit tubing. We also attached our hospital wall vacuum through a pressure regulator (Ohio PISA, manufacturer, location) set to maximum (0.13 kPa) to a 2 L suction canister, then to the filter and box. In our practice, the patient is covered with a sheet or surgical drape ( Figure 1B ). To simulate viral aerosol contamination and clearance, an aerosol particle generator (TSI 8026, manufacturer, location) was placed inside the covered 35x45x50 cm plexiglass (?) box. An aerosol particle counter (TSI PortaCount 8048, manufacturer, location) was connected to a 135 cm long sampling tubing inside the box. To measure baseline particle clearance without vacuum applied, we created a stabilized elevated particle count (2.5 -6 x 10 4 particles cm -3 ); the particle generator was then turned off and particle count data sampled at 15 s intervals in technical replicates. For active aerosol removal, the vacuum source was turned on at the moment when the particle generator was turned off. Normalised counts were fit as exponential decays (r 2 >0.95, Matlab, manufacturer, location) and half-lives analysed by one-way ANOVA (Prism 7, manufacturer, location) with significance set to p<0.05 and Tukey's post hoc pairwise comparisons test. The 3.4 min half-life baseline aerosol clearance was reduced to 1.0 min with the wall vacuum, 0.28 min with the 23 CFM vacuum, and 0.14 min with 60 CFM vacuum ( Figure 1C , one-way ANOVA, F(3,9)=52, overall p<0.0001). The two stand-alone vacuum configurations were not statistically distinguishable (p=0.97), though clearance half-lives for each vacuum were shorter than with no vacuum (Figure 1C inset, ANOVA post hoc Tukey's test: p=0.001 for passive vs wall suction, p<0.0001 for passive vs 60 CFM, p<0.0001 for passive vs 23 CFM). We applied a vacuum and viral filter to an enclosed intubation box and determined aerosol clearance times in order to establish parameters for time-to-removal after use. Enclosed boxes with vacuums capable of filtering SARS-CoV-2 dispersed during aerosol-generating procedures are likely safer compared to intubation boxes open to the room. The National Institute of Occupational Safety and Health (NIOSH) "hierarchy of controls" prioritizes engineering and administrative controls over personal protective equipment (PPE) for mitigating occupational hazards, and PPE is considered the least effective (albeit indispensable) control. 7 Although we promote this engineering control, proper PPE is still recommended despite any additional benefits offered by our system. The Occupational Safety and Health Administration (OSHA) recommends US operating rooms maintain a minimum of 15 air changes per hour, equivalent to 99% aerosol removal in 18 min. 8 Both 23 and 60 CFM vacuum pumps reached 99% clearance of the box in 90 s, and likely reduce collateral contamination of other operating room equipment. The reusable 23 CFM vacuum costs $20, and could save several hundred dollars in operating room time per use. 9 Our hospital wall suction significantly reduced clearance times also, but flow rates for wall suction are not routinely controllable nor determinable in clinical practice, precluding broad extrapolation. Aerosol levels outside the box were not assessed, but gases suctioned through a viral filter with 99.9999% efficiency exceed recommended air quality regulations. For longer procedures necessitating aerosol removal, ear plugs should be used and pressures considered. 10 Improvements towards lightweight and/or disposable barriers combining various features can be readily envisioned. Our design may afford improvements in proceduralist mobility restrictions and emergency access to patients, though further testing is warranted to verify patient safety. 4 Improvements in control of perioperative inhalational risk may be an unexpected lasting impact shown with the working window sealed with a gown (disposable) clipped into place, affording proceduralist arm mobility, aerosol enclosure, and vacuum elimination. The gown can be easily detached during airway rescue. C. Aerosol elimination follows exponential decay kinetics, with hospital wall vacuum and two commercial vacuums improving clearance kinetics. D. Vacuum aerosol removal significantly decreases particle clearance half-lives from 3.4 min (passive) to 1.0 min (wall suction), and to 0.28 min with the 23 cubic feet per min (CFM) vacuum, or 0.14 min with a 60 CFM vacuum. Time series from replicate experiments from 1C were fit to exponential decays after normalisation, and average half-lives (t 1/2 ) were analysed by one-way ANOVA (F (3, 9) =52, overall p<0.0001). Aerosol clearance was significantly hastened with suction from the wall vacuum, and with the 23 or 60 cubic feet per minute (CFM) stand-alone vacuums vs passive clearance (*** p=0.0001, **** p<0.0001, ANOVA with Tukey's multiple comparisons testing, error bars represent standard deviation). Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1 Taiwanese doctor invents device to protect US doctors against coronavirus More on Barrier Enclosure during Endotracheal Intubation. Reply A multipurpose portable negative air flow isolation chamber for aerosol-generating procedures during the COVID-19 pandemic MSKCC COVID Safety Innovations Team. Intubation-Extubation Boxes v3: Thinking Inside the Box. 2020 Breathing Circuit Filters by Recommended Application -For use with Anesthesia Machine Breathing Circuits National Institute for Occupational Safety and Health National Institute for Occupational Safety and Health. Hierarchy of Controls Guidelines for Environmental Infection Control in Health-Care Facilities Understanding Costs of Care in the Operating Room A Rapidly Deployable Negative Pressure Enclosure for Aerosol-Generating Medical Procedures We are grateful for the assistance of the following members of Memorial Sloan Kettering Cancer Center: Ying Zhen for access to instruments, Alexander Tanchoco for helpful discussions, Craig Goulbourne for construction and design input in assembling intubation boxes, and Gregory W. Fischer for departmental support. No compensation was provided for their assistance of this project.