The Aerosol-Danger of SARS-Cov-2
The outbreak of the SARS Coronavirus-2 (SARS-CoV-2) in China 2019 has within a short time spread around the globe and is just about to hit central Europe. Although about 80% of all confirmed cases develop a mild febrile illness, around 17% develop severe Corona viral disease (COVID-19) with findings of acute respiratory distress syndrome (ARDS), of which about 4% will require mechanical ventilation.
Since this virus, which was previously unknown to humans, spread rapidly around the globe, a large number of patients requiring intensive medical care now arise within a very short time.
The lungs are the organs most affected by COVID-19 because the virus accesses host cells via the enzyme ACE2, which is most abundant in type II alveolar cells of the lungs. This results in mainly type 1 respiratory failure, which often requires urgent tracheal intubation and mechanical ventilation.
Due to viral shedding in the patient's lungs, COVID-19 spread mainly via droplets. Events like coughing, high flow nasal oxygen (High-Flow), intubation and more can cause aerosol generation, allowing these airborne particles to travel even further distances.
Performing endotracheal intubation in these patients is, therefore, a high-risk procedure, and it is required to adhere to certain principles to avoid infection of health care providers.
The Safe Airway Societies of Australia and New Zealand have published a consensus statement that describes the problem very well and provides practical tips based on the currently available evidence.
1. Non Invasive Ventilation (NIV) and High Flow Nasal Oxygen (High-Flow)
Current evidence suggests that the failure rate of NIV in COVID-19 patients seems to be similarly high as observed among Influenza A patients. Failure in these patients resulted in higher mortality.
In general, NIV is recommended to be avoided or at least used very cautiously!
The utility of High-Flow in viral pandemics in unknown. There is some evidence suggesting a decreased need for tracheal intubation compared to conventional oxygen therapy.
High Flow Nasal Oxygen is worth a try, although it has to be assumed, that this is aerosol-generating.
High-Flow should only be used in (negative pressure) airborne isolation rooms, and staff should wear full personal protective equipment (PPE) including N95/P2 masks.
NIV and High-Flow are NOT recommended for patients with severe respiratory failure or when it seems clear that invasive ventilation is inevitable!