Aerosol boxes and COVID-19 | Association of Anaesthetists
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Aerosol boxes and COVID-19

Study shows that aerosol box used to protect healthcare workers during COVID intubation increases, rather than decreases, exposure to airborne particles

A new study shows that aerosol boxes that have been manufactured and used in hospitals in the UK and around the world in order to protect healthcare workers from COVID-19 can actually increase exposure to airborne particles that carry the virus, and thus casts doubt on their usefulness. 

The authors – who include Drs Peter Chan, Joanna Simpson and colleagues, Intensive Care and Anaesthesia Specialists at Eastern Health, Melbourne, VIC, Australia – say that “the consequences of promotion of such untested devices include either a false sense of security using these devices, or paradoxical increase in healthcare workers exposure to COVID-19”. The study is published in Anaesthesia (a journal of the Association of Anaesthetists).

The danger posed to frontline health workers exposed to infectious COVID is significant. The sickest COVID patients often need to be placed onto a ventilator, which is also when the risk to the health worker of exposure to virus is potentially at its greatest.  This has created a race to manufacture aerosol containment devices including improvised protection strategies and devices for use during tracheal intubation. This has taken on even greater urgency in the last week, with a global “second wave” becoming more likely, and a recent open letter to the World Health Organization from 239 global scientists in 32 countries warning that we have probably been severely underestimating the amount of COVID-19 spread through fine aerosol droplets over large distances. 

Aerosol boxes have been promoted by multiple worldwide news organisations in print, television, online and across social media (see examples below) as not only a quick and simple solution to protecting frontline workers but also an example of private industries stepping up production to support frontline healthcare workers. However, these devices were produced outside the normal regulatory framework, and thus were never clinically tested or validated for effectiveness and safety. They were subsequently heavily promoted in the media and on social media. Yet despite this heavy promotion, no international guideline on personal protective equipment (PPE) has ever endorsed their use. 

In recent months there have been increasing concerns from the medical community that these devices might be either not helping, or potentially exposing frontline medical staff to unforeseen harm, but as this could not be proven, the devices continued to be used across the globe. In this new study, Drs Chan and Simpson and colleagues partnered with Ascent Vision Technologies, a Melbourne-based engineering company, to test the effectiveness of varying methods of aerosol containment, including the so-called aerosol box (see links to photos below), which various private companies have offered their services to manufacture.    

The study was carried out in a self-contained intensive care unit room using seven adult volunteers (four male, three female), who took turns in random order acting as the patient or the doctor (person performing the intubation). The study simulated exposure of the laryngoscopist to airborne particles sized 0.3 - 5.0 microns using five aerosol containment methods (aerosol box; sealed box with and without suction; vertical drape; and horizontal drape) compared with no intervention. As each of the seven volunteers did all six trials (the five interventions plus no intervention), the study generated 42 sets of results. 

To simulate aerosolisation, the patient volunteer held a bottle of fluid just under their mouth, and coughed every 30 seconds. Over five minutes particle detection devices were used to count different sized particles and assess particle spread. 

Compared with no device use, the aerosol box surprisingly showed an increase in airborne particle exposure of all sizes over 5 minutes. This suggests that this aerosol box was increasing exposure to COVID-19 particles, often by a factor of 5 times or more. 

The authors say: “We were surprised to find airborne particle contamination of the doctor increased substantially using the aerosol box compared with all other devices and with no device use. Spikes of airborne particles were clearly seen, coinciding with patient coughing. We hypothesise that these represent particles escaping from the arm access holes in the aerosol box.”

The authors say: “The race to generate sustainable equipment to protect healthcare workers during intubation procedures in patients with suspected or proven COVID-19, particularly in settings where PPE supply is limited, has flooded the scientific community and social media with a variety of novel devices meant to contain potentially infectious aerosols produced by patients. Evidence for the safety and efficacy of these devices is lacking.”

They conclude: “This study demonstrates that devices such as the aerosol box we tested – which is typical of designs used worldwide – confer minimal to no benefit in containing aerosols during an aerosol-generating procedure and may increase rather than decrease airborne particle exposure. The use of any aerosol containment device has been eliminated from our intubation protocols until their safety can be properly established.”

Dr Chan adds: “If this box were a sold as a product, and therefore regulated, it would likely need to be immediately recalled due to a potential infection risk to the healthcare worker. Unfortunately, because these devices have been donated and are not regulated in any way, healthcare workers might be continuing to increase their exposure to COVID-19 while thinking they are protecting themselves.”

Read the full study