key: cord-0986805-ngcrcowg authors: Roth, Benjamin S.; Moschella, Phillip; Mousavi, Ehsan S.; LeMatty, Amanda S.; Falconer, Robert J.; Ashley, Noah D.; Mohammadi Nafchi, Ali; Gaafary, Chris; DesJardins, John D. title: Development and efficacy testing of a portable negative pressure enclosure for airborne infection containment date: 2022-01-22 journal: J Am Coll Emerg Physicians Open DOI: 10.1002/emp2.12656 sha: 181fd6309be1bd1dcf2511af5cc0dfa785eaac90 doc_id: 986805 cord_uid: ngcrcowg OBJECTIVES: To overcome the shortage of personal protective equipment and airborne infection isolation rooms (AIIRs) in the COVID‐19 pandemic, a collaborative team of research engineers and clinical physicians worked to build a novel negative pressure environment in the hopes of improving healthcare worker and patient safety. The team then sought to test the device's efficacy in generating and maintaining negative pressure. The goal proved prescient as the US Food and Drug Administration (FDA) later recommended that all barrier devices use negative pressure. METHODS: Initially, engineers observed simulations of various aerosol‐ and droplet‐generating procedures using hospital beds and stretchers to determine the optimal working dimensions of the containment device. Several prototypes were made based on these dimensions which were combined with filters and various flow‐generating devices. Then, the airflow generated and the pressure differential within the device during simulated patient care were measured, specifically assessing its ability to create a negative pressure environment consistent with standards published by the Centers for Disease Control and Prevention (CDC). RESULTS: The portable fans were unable to generate any airflow and were dropped from further testing. The vacuums tested were all able to generate a negative pressure environment with the magnitude of pressure differential increasing with the vacuum horsepower. Only the 3.5‐horsepower Shop‐Vac, however, generated a −3.0 pascal (Pa) pressure gradient, exceeding the CDC‐recommended minimum of −2.5 Pa for AIIRs. CONCLUSION: A collaborative team of physicians and engineers demonstrated the efficacy of a prototype portable negative pressure environment, surpassing the negative pressure differential recommended by the CDC. As the COVID-19 pandemic outstripped worldwide supplier of personal protective equipment (PPE) and airborne infection isolation rooms (AIIRs), many clinicians and investigators sought to build devices to increase healthcare worker (HCW) safety, especially during aerosolgenerating procedures such as intubation. A plethora of devices were developed and published. Many of the initial devices were passive barrier protection devices, including the quintessential example of the acrylic aerosol box. 1 These passive barrier devices were meant to restrict the spread of viral particulates-both aerosols and dropletsaway from HCWs by using a physical obstruction to particulate movement such as a plastic sheet or acrylic wall. Later devices incorporated some degree of negative pressure, ranging from connection to wall suction to attachment of small portable suction devices all the way to incorporation of industrial air scrubbers attached to multiple containment devices at once. [2] [3] [4] As highlighted by a review by Sorbello et al, many of these devices were published without any testing to prove efficacy, either in protecting the HCWs or in ensuring the safety of patients within the device during use. 5 Moreover, these devices almost universally expected HCWs to remain in full PPE, and unfortunately, many of the devices may increase the risk of HCW PPE integrity breaches. 5 Testing the devices' efficacy is essential to determine which devices, if any, should be further tested in a clinical environment to possibly improve HCW safety while maintaining patient safety. The passive barrier devices, for example, "may not be effective in decreasing healthcare provider exposure to airborne particles, and in some circumstances, may instead increase HCP exposure," as highlighted by the US Food and Drug Administration (FDA) in August 2020. 6 A proposed mechanism for this increased risk is that the air within the barrier is highly concentrated with viral particulates and that any changes in air pressure within the device-from coughing, for instance-could channel highly infectious air toward HCWs performing patient care at the device ports. 5 Unfortunately, the passive barriers' possible harm to HCWs was stated months after they were initially granted Emer- The device uses a rigid, polyvinyl chloride (PVC)-based frame covered in a transparent plastic sheet with a connected sound-isolated vacuum . The COVER patient enclosure features a polyvinyl chloride frame with a transparent plastic sheet. The edge of the sheet is highlighted (+) and drapes over a patient's torso. The highlighted filter boxes (#) are cardboard boxes covered in duct tape. Tubing (white arrows) connects the patient enclosure's filter boxes to the sound-isolating box (black arrow). The sound-isolating box has an exhaust on the side opposite the tubing entrance. The construction diagram shows the patient enclosure when looking from the head of the bed (top) and from the side (bottom) along with an angled approach (right). The protrusions from the frame (black arrows) in the construction diagram can be rotated any direction to anchor the device cleaning between uses and allowed for an additional HEPA filter on the vacuum exhaust. The developed prototype was called the Covering for Operations during Viral Emergency Response (COVER). The device frame, connecting tubes, sound-isolating box, and vacuum are all reusable after cleaning. Cleaning can be performed with local hospital-approved sanitization procedures, such as those used for cleaning and sanitizing any normal piece of equipment in the hospital room. Because of their proximity to the patient, the HEPA filters and transparent plastic sheet were intended to be replaced between patient encounters. To overcome supply and logistical barriers to adequate personal protective equipment and airborne isolation rooms, an interdisciplinary team of engineers and clinical physicians developed a novel, negative pressure patient care enclosure. Using simulations of aerosol-producing and dropletproducing procedures, the team developed and demonstrated the efficacy of a prototype portable negative pressure environment that surpassed the negative pressure differential recommended by the Centers for Disease Control. To ensure the fire and sound safety of the vacuum running while enclosed in these custom sound-isolating boxes, a trial of the largest horsepower vacuum set to run continuously for 50 hours was performed in an outdoor setting. The temperature inside the soundisolating box and the noise level outside the box were continually measured using the commercially available Bluetooth Char-Griller Remote Grill Thermometer (Char-Griller, Atlanta, Georgia) and an Apple Watch Series 5 (Apple, Cupertino, California), respectively. To assess for device efficacy, the airflow generated by the device using either the fans or the various vacuums was tested in an unused hospital room. This airflow testing was performed using a TSI-ALNOR EBT-731 (TSI Incorporated, Shoreview, Minnesota) capture hood and reported in cubic feet per minute. To determine the total airflow capacity of the system, the airflow rates of the isolated filter boxes separated from the fully constructed Linear perforation guides with 5-cm increments are noted by black lines (highlighted by black arrows) along the top, side, and head-of-the-bed device sides to facilitate patient care from a variety of sites depending on the required clinical activity. The device width allows for use on narrow gurneys as well as full hospital beds edges would normally be unsealed in clinical use and were unsealed for later pressure differential measurement, measuring the device's total airflow capacity required them to be sealed. The airflow was again tested both with and without filters present to measure the degree of increased impedance to flow caused by the filter material. To determine whether a negative pressure environment was created, the pressure differential between the air within the transparent device hood and the air outside the device was measured continuously within an unused hospital room. A negative pressure differential, meaning the air pressure within the device is lower than the pressure external to the device, should prevent air escape both at intentional functional access ports and at transient barrier gaps generated by patient movement. A full device material list with costs as sourced from a local hardware store is shown in One of the sound-isolating boxes and the largest vacuum ran continuously for 50 hours to measure operating temperatures and noise generation; a thunderstorm disrupted power to the vacuum for 10 seconds during this trial. The temperature within the sound-isolating box ranged between 118 • F and 162 • F after an initial start- The airflow measurements are displayed in Table 2 . The fans as part of the fully constructed device did not generate any measurable airflow and were dropped from subsequent testing. The data showed that the HEPA filters produce impedance to airflow but that increased airflow was observed with increasing vacuum horsepower. The pressure measurements generated under the varied test scenarios are shown in Table 3 . The data showed that with increased vacuum horsepower there was also an increase in the negative pressure environment generated within the device. The highest measured airflow rates and pressure differentials were observed with the 3.5-horsepower vacuum, and the lowest observed pressure differentials were observed using the 1.6-horsepower vacuum. Importantly, however, all of the vacuums generated an observable negative pressure environment even with a simulated patient and 60 cm of access cuts made into the device (Table 4 ). The COVER device prototype is designed to overcome the scarcity of negative pressure isolation rooms and provide an increased level of safety for HCWs. Currently designed AIIRs limit the spread of airborne infections outside of the room but provide little protection while inside the room. This device could increase staff safety by reducing the number of viral droplets and aerosols in the ambient air surrounding a patient, whether in an AIIR, a normal patient room, or even an emergency department hallway. The device may help overcome critical N95 supply shortages, for instance, by allowing HCWs proximity to the patient without N95 respirator use, although this would require additional study to prove safety. Moreover, to our knowledge, this is the first novel negative pressure environment made exclusively of non-medical supplies that has been tested for efficacy in generating the CDC's goal pressure of −2.5 Pa. Using the device with the 3.5horsepower vacuum generated a pressure differential more than this ideal pressure differential even with a simulated patient and 60 cm of access ports. The device could, therefore, increase the availability of negative pressure environments to meet widespread need during this or future pandemics even if traditional medical supplies are depleted. Overall, safety during intubation and other time-sensitive procedures would require further study and dedicated clinician training to lessen any potential impact on successful completion of these procedures. Although some of the first published devices were passive barrier acrylic boxes, many subsequently published devices included a combination of a plastic tent or a plastic sheet over a rigid frame, employing wall suction or small vacuums for flow generation. Many of these devices feature a single HEPA filter if they include a filter at all. The COVER device's 2 intake HEPA filters, which provide more surface area to minimize flow impedance, still required a 3.5-horsepower vacuum to generate a pressure differential of −2.5 Pa. Although the efficacy of other published devices was not directly tested, their ability to generate necessary pressure differentials with smaller-and thus higher impedance-HEPA filters and less powerful flow-generation devices seems unlikely. Therefore, although the COVER's device containment structure is similar to other devices with a plastic sheet over a rigid frame, the COVER device is unique among published devices in its ability to generate a negative pressure environment commensurate to CDC specifications. The testing process for airflow rates and for negative pressure generation is also unique among published devices. Many devices used visual droplet and aerosol testing to highlight the possible safety improvements to HCWs-in other words, fewer particulates were noted to have contaminated HCWs in proximity to or performing care within the enclosures during testing. 5 With regard to airflow testing, one device verified that flow persisted even after the application of an HME filter but did not further test if negative pressure within the enclosure was observed. 10 Both the airflow testing and pressure differential testing process highlighted in this article could serve as a guide for future device design and efficacy testing, especially for prototypes of similar negative pressure barriers. Unfortunately, the COVER device's success in generating airflow and a negative pressure environment with the vacuum came at the expense of increased sound generation. While the level of sound generated was mitigated by the sound-isolating box, the increased noise production makes conversation more difficult, although regular vol- The device was tested within the hospital setting on both emergency department gurneys and hospital beds in unused hospital rooms to approximate real-world application. Device assembly and use during testing, though, was solely by the team of engineers and physicians who worked to develop the device. Therefore, the measured airflows and pressure differentials represent the idealized system implementation; widespread implementation by hospital staff less well versed in the device may result in reduced airflow and lower overall pressure differentials. The simulated patient for testing was roughly 6 feet tall and of average build; further testing for comfort and efficacy for a wider variety of patient body types would be required before wider clinical implementation. In addition, although the simulated patient did move spontaneously during testing, real-world patient movements add a level of uncertainty that is difficult to fully predict, adding unintended leaks to the system. Depending on the magnitude and frequency of these movements, the device may have difficulty maintaining its negative pressure environment. Finally, whether a continuous negative pressure environment is maintained after hours of use and during a procedure such as intubation has not yet been directly studied. To overcome some of these limitations, a future iteration of the device would hopefully incorporate a visual indicator on the device to show HCWs appropriate negative pressure was being maintained during use; this indicator could serve as a warning that too many perforations were created, the vacuum was not performing as expected, or the HEPA filters required replacement. The COVER device uses off-the-shelf, non-medical components to generate a negative pressure environment in excess of −2.5 Pa as tested using a simulated patient and 60 cm of patient care access cuts. Further research will be needed to assess the device's patient and clinician usability along with the device's effectiveness in true droplet and aerosol containment. 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Occupational noise exposure The qualitative evaluation of the limitation of aerosol spread by a transparent intubation box Method to reduce aerosolized contaminant concentration exposure to healthcare workers during the COVID-19 pandemic when temporary isolation systems are required The authors declare no conflicts of interest.