New Study Debunks WHO Stance on Risks of Facemask Ventilation During Surgery
A new study from the UK suggests that OR nurses, CRNAs and other surgical staff might soon be free to dispense with the time-consuming Covid-19 safety procedures such as having to don (and work under) additional layers of PPE and ½-hour delays for air changes.
According to a paper just published in Anaesthesia (a journal of the Association of Anaesthetists), the use of facemask ventilation during routine surgery should not be classed as an aerosol-generating procedure and does not increase the risk of COVID-19 transmission compared with normal breathing/coughing of patients.
Concerns about SARS-CoV-2 transmission prompted the World Health Organization (WHO) to classify facemask ventilation as an ‘aerosol-generating procedure’ (AGP), and the safety guidelines have impaired efficiency and processes in surgical theaters around the world. The evidence supporting the WHO AGP classification is primarily based on a 2003 study of infections in anaesthetists during the SARS-1 epidemic.
However, authors of the Anaesthesia study state that “There is no direct evidence to indicate whether facemask ventilation is a high-risk procedure for aerosol generation.” In fact, this paper appears to be the first study to actually monitor and measure aerosol concentrations generated during facemask ventilation.
Following the WHO AGP designation and current pandemic guidance, anesthetists performing facemask ventilation in patients at risk of having COVID-19 have been wearing a respirator mask, eye protection and additional personal protective equipment. The guidelines apply to nearby theatre staff as well. In addition, extra time (up to half an hour per case) must be added to each operation to allow sufficient air changes in theatre to remove any of the presumed infectious aerosol. The time-consuming safety restrictions significantly reduce the number of procedures that staff can perform each day, especially those involving urgent or emergency surgery, and increase the backlog in the healthcare system.
In this new study, the authors conducted aerosol monitoring in anaesthetized patients during standard facemask ventilation, and facemask ventilation with an intentionally generated air leak – to mimic the worst-case scenario where aerosol might spread into the air. Recordings were made in ultraclean operating theatres (at Southmead Hospital, North Bristol NHS Trust, UK) and compared against the aerosol generated by each patient’s normal breathing and coughing.
Respiratory aerosol from normal breathing was reliably detected above the very low background particle concentrations with median aerosol concentration of 191 particles per liter. The average aerosol concentration detected during facemask ventilation without a leak (3 particles per liter) was 64-times less than that for breathing. When an intentional leak was introduced the aerosol count was 17 times lower than breathing (11 particles per litre).
When looking at peak particle concentrations the team found that a patient coughing produced a spike of 1260 particles per liter, compared to the peak of 60 per liter (20 times lower) for regular facemask ventilation and 120 per liter with an intentional leak introduced (10 times lower).
Dr Andrew Shrimpton, the lead author of the study, commented: “This study demonstrates that facemask ventilation, even when performed with an intentional leak, does not generate high levels of bioaerosol.”
The authors add: “The low concentration of aerosol detected during facemask ventilation even with an intentional leak is also reassuring given that this represents a worst-case scenario. Both normal breathing and a voluntary cough generate many-fold higher quantities of aerosol than facemask ventilation… On this basis, we believe facemask ventilation should not be considered an aerosol-generating procedure. Accumulating evidence demonstrates many procedures currently defined as aerosol-generating are not intrinsically high risk for generating aerosol, and that natural patient respiratory events often generate far higher amounts.”
They conclude: “The emerging evidence from quantitative clinical aerosol studies is yet to be incorporated into clinical guidance for aerosol-generating procedures and we believe this needs urgent reassessment. Declassification of some of these anesthesia-related procedures as aerosol-generating would seem appropriate due to their lack of aerosol generation. Our findings also raise the broader question of whether the term ‘aerosol-generating procedure’ is still a useful concept for anaesthetic airway management practice in the prevention of SARS-CoV-2 or other airborne pathogens.”
Dr Mike Nathanson, President of the Association of Anaesthetists said: “This important work will allow clinicians to better understand the risks of general anesthesia in patients with Covid. As we enter another winter, and with a high prevalence of Covid, the backlog of surgical cases is increasing. Anesthetists will wish to carry on working for as many of their patients as possible. As the authors suggest, this research will inform the debate on how we can work safely.”
This study is the result of a collaboration between Anaesthetic and Aerosol research groups based in Bristol, UK and Melbourne, Australia as part of the NIHR funded AERATOR study. The results reinforce the findings of similar studies performed by the AERATOR group demonstrating many anesthetic procedures are not high risk for aerosol generation.