Improved Testing and Design of Intubation Boxes During the COVID-19 Pandemic

Abstract

Study objective: Throughout the coronavirus disease 2019 pandemic, many emergency departments have been using passive protective enclosures ("intubation boxes") during intubation. The effectiveness of these enclosures remains uncertain. We sought to quantify their ability to contain aerosols using industry standard test protocols.

Methods: We tested a commercially available passive protective enclosure representing the most common design and compared this with a modified enclosure that incorporated a vacuum system for active air filtration during simulated intubations and negative-pressure isolation. We evaluated the enclosures by using the same 3 tests air filtration experts use to certify class I biosafety cabinets: visual smoke pattern analysis using neutrally buoyant smoke, aerosol leak testing using a test aerosol that mimics the size of virus-containing particulates, and air velocity measurements.

Results: Qualitative evaluation revealed smoke escaping from all passive enclosure openings. Aerosol leak testing demonstrated elevated particle concentrations outside the enclosure during simulated intubations. In contrast, vacuum-filter-equipped enclosures fully contained the visible smoke and test aerosol to standards consistent with class I biosafety cabinet certification.

Conclusion: Passive enclosures for intubation failed to contain aerosols, but the addition of a vacuum and active air filtration reduced aerosol spread during simulated intubation and patient isolation.

Figure 1

Comparison of passive and active rigid plastic barrier enclosures. A, Commercially available passive intubation box. B, Aluminum-reinforced rigid plastic barrier enclosure with 3-dimensionally printed adapter to allow active air filtration.

Figure 2

Active rigid plastic barrier enclosures. A, Computer-aided design depiction of a rigid plastic barrier enclosure with external ultralow particulate air filter cartridge and DeWalt portable vacuum (left) and with the Buffalo Filter smoke evacuator (right). B, Computer-aided design illustration of the 2 primary PAO aerosol measurement locations. C, The unit in patient isolation mode, with the head of the bed elevated to 60 degrees. The subject is a member of the research team.

Figure 3

Simulated intubation. Comparison of a passive intubation box (A) and an enclosure with active air filtration (B), using a neutrally bouyant glycol smoke. The smoke exited the intubation box in both the cranial and caudal locations in the passive condition, but was fully contained in the active configuration.

Figure 4

Results of aerosol concentration measurements. Relative concentration percentages of aerosolized PAO are plotted on a log scale for each test configuration. Measurements were taken simultaneously at 2 locations (proceduralist, black circles; assistant, gray circles). Blue diamonds represent the median of all measurements for a given configuration. The horizontal dotted line represents the acceptable standard for aerosol concentration (<0.01%) outside the rigid plastic barrier enclosure.