New research published in Anesthesia (a journal of the Association of Anesthetists) disputes the guidance that special aerosol precautions are required only when using oxygen therapy for COVID-19 patients and raises concerns about the safety of staff and patients in hospital wards if they are not protected from infectious aerosols. .
The study began to examine whether oxygen treatments used in patients with severe COVID-19 produce large amounts of small respiratory particles called aerosols, which can transmit the virus and can avoid the usual precautions used in hospitals. The study found that these oxygen treatments do not produce excessive amounts of aerosols and actually reduce aerosols suggesting that these treatments can be widely available.
The study also showed that respiratory activities such as coughing and deep breathing are important sources of aerosol particles and this has the potential to expose healthcare workers to an increased risk of infection. Importantly, the authors make it clear that this study used 10 healthy volunteers to produce the measured aerosols, not patients infected with SARS-CoV-2.
The study authors include Dr. Nick Wilson (Royal Clinic of Edinburgh, NHS Lothian, Scotland), Professor Euan Tovey (University of Sydney), Professor Guy Marks (University of New South Wales, Sydney) and Tim Cook (Royal The United Hospitals Bath NHS Foundation Trust, Bath, UK) says their findings could partly explain why staff working in wards wearing only surgical masks have about two to three times higher rates of infection and hospitalization. than those working in the ICU where more personally protected Protective equipment such as N95 / FFP3 respirators are used.
The researchers created a new chamber that provides extremely clean air, in which sat 10 healthy volunteers. They breathed into a large cone, and the researchers collected the exhaled particles and used a specialized machine called an “optical particle counter” to measure the number and size of the particles. In contrast to previous studies, the researchers collected almost all the particles that breathe, and this allowed a clear comparison between the amounts of aerosols created by respiratory activities and oxygen therapies.
First, the volunteers performed respiratory activities, such as breathing, speech, shouting, coughing, and exercise, designed to mimic the respiratory activity of patients with respiratory infections such as COVID-19. This has shown that the increased respiratory activity (such as coughing and deep breathing) that is common in patients with COVID-19 increases aerosols by more than 100-fold.
The volunteers then repeated the experiments while receiving oxygen treatments commonly used in hospital patients with severe COVID-19, first delivering high-flow oxygen to the nose (high-flow nasal oxygen) and then delivering oxygen under pressure through a mask. (non-invasive ventilation). Aerosol counts did not increase during increased respiratory activity and actually decreased.
There is much debate about the role of respiratory particles in COVID-19 transmission prevention guidelines. Larger particles (larger than 1/200 of a millimeter) are traditionally called “droplets” and are thought to travel only 1-2 meters from an infected patient before falling to the ground. Aerosols are smaller particles (less than 1/200 of a millimeter) and remain suspended in the air for extended periods, spread further, may accumulate in low-ventilation areas, inhale deep into the lungs, and bypass looser placements. Many current guidelines are designed to protect against droplets, and aerosol contamination is only considered a risk when caused by medical treatments. In this new study, volunteers produced up to 100 times more aerosol particles with activities such as coughing than they did during oxygen therapy.
This calls into question current guidelines stating that healthcare staff caring for COVID-19 patients who cough and have difficulty breathing only need PPE to protect against larger droplets. “Drop protection” includes surgical masks but does not prevent aerosol particles from passing around the edges of the masks and being inhaled. N95 / FFP3 respirators that fit and filter better block more aerosols, but the guidelines only recommend this for staff caring for patients receiving advanced oxygen therapy.
Dr Nick Wilson, lead author of the study, explains: “More than 90% of the total number of particles produced by both the activity and the treatment were the smaller aerosols. Aerosols are important as they can travel long distances in the air, “Avoid loose surgical masks and be inhaled deep into the lungs. This raises safety concerns for those around COVID-19 patients.”
Professor Euan Tovey says: “The cough and shortness of breath that are common in patients with COVID-19 produce far more droplets and aerosols than those produced by patients treated with oxygen. Surgical masks provide insufficient protection against aerosols and staff safety can only be increased with the wider use of specialized respirators (N95 or FFP3) and increased indoor ventilation. Also, as respiratory treatments did not significantly increase aerosols, these treatments should be widely available to patients with COVID-19 who need them. “
Professor Guy Marks says: “The study also has implications beyond hospitals. The production of both droplets and especially aerosols with daily breathing activities reinforces the importance of maintaining social distance, excellent ventilation in buildings and transport, to “are outside where possible and use effective masks. And to protect against respiratory virus and reduce the amount of virus that spreads during respiration.”
Professor Tim Cook concludes: “Our findings strongly support the reassessment of guidelines for better protection of hospital staff, patients and all those at the forefront of dealing with or suspected of having , COVID-19 “.
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