31 Aug 2020

Global caution on use of aerosol boxes in treating COVID-19 patients

Diagram of an aerosol box. Image: Peter Chan
Two Australian studies lead to a global caution on use of aerosol boxes in treating COVID patients – with one warning it increases exposure by up to 500%.

The US Food and Drug Administration (FDA) has urgently withdrawn approval for the use of aerosol boxes that have been used globally to protect healthcare workers from COVID-19.

Studies have found that these boxes potentially increase the healthcare worker’s risk of exposure to aerosolized and droplet particles that potentially contain SARS-COV-2, the virus that causes COVID-19, by up to 500%.

The FDA cited just two published papers in its warning sent out this week, both from researchers at Monash University Faculty of Medicine, Nursing and Health Sciences.

Dr Peter Chan, who is doing an NHMRC-sponsored PhD at the Monash School of Public Health and Preventive Medicine, co-wrote one paper cited by the FDA, and Associate Professor David Brewster, from the Monash University Central Clinical School, who co-wrote the original research paper with Dr Jonathan Begley from Cabrini Hospital – both published in Anaesthesia, the journal of the Association of Anaesthetists in the UK.

The studies raise concerns over the widespread adoption of devices and treatments before they have been fully tested.

COVID-19 patients placed on ventilators are very sick, and very infectious, having a high load of the virus. Placing these patients on a ventilator puts healthcare personnel (HCP) at increased risk of also contracting the disease.

The need to protect doctors and nurses led to a flood of “aerosol boxes” being developed and sold globally as a protection, made more urgent after an open letter to the World Health Organization (WHO) from 239 global scientists in 32 countries warning about an underestimation of the amount of COVID-19 spread through fine aerosol droplets over large distances. On Wednesday, July 8, WHO formally acknowledged this emerging evidence regarding potential spread of COVID-19 through these tiny droplets.

However, the bulk of the aerosol boxes 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.

Aerosol boxes are transparent devices designed to cover a patient’s head and upper body that incorporates one or more ports through which the HCP’s hands are passed to perform medical procedures, and that does not include fans, air filters, or other features and is not intended to generate negative pressure. In May the FDA released what is called an umbrella emergency use authorization for its use in procedures like intubation and airway clearance.

Dr Chan and his 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.

The study was carried out in a self-contained intensive care unit room at Box Hill Hospital, Melbourne, using seven adult volunteers (four male, three female), who took turns in random order acting as the patient or the doctor (the person performing the intubation). The study simulated exposure of the doctor 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.

The study found that - compared with no device use - the aerosol box surprisingly showed an increase in airborne particle exposure of all sizes over 5 minutes. According to Dr Chan, assuming that COVID-19 particles act in the same way as the fluid used in this simulation, the results of this study suggest that this aerosol box was increasing exposure to COVID-19 particles, in some cases 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 believe that these represent particles escaping from the arm access holes in the aerosol box."

They add: "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."

The Chan study follows on from a landmark study published in May 2020 led by Dr Jonathan Begley and Associate Professor David Brewster, in which the Monash and Cabrini researchers found that the aerosol boxes often rip protective gear when medical staff put their arms through the holes.

This world-first research at Cabrini demonstrated that the life-saving procedure of intubation when performed by 12 anaesthetists with these aerosol boxes took too long to complete. Using mannequins, the study found that doctors spent up to three minutes intubating patients using the box, compared with less than one minute without it.  That could be the difference between life and death for seriously ill patients who desperately need air flow, according to researchers. According to Associate Professor Brewster, this study was “critical in the FDA deciding to outlaw the use of these aerosol boxes,” he said.

Media: 29 August 2020 The Australian, "Coronavirus: infection shield to keep medical staff safe ‘increases risk 500pc’"

  • Simpson J.P, et al., Measurement of airborne particle exposure during simulated tracheal intubation using various proposed aerosol containment devices during the COVID‐19 pandemic, Anesthesia, 19 June 2020, 1-9. doi: 10.1111/anae.15188
  • Begley J.I. et al., The Aerosol box for intubation in COVID-19 patients: an in-situ simulation crossover study, Anesthesia, August 2020. 75 (8), 1014-1021. doi: 10.1111/anae.15115
    See also 19 May feature story.

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