Assessment of dispersion of airborne particles of oral/nasal fluid by high flow nasal cannula therapy

Abstract

Background Nasal High Flow (NHF) therapy delivers flows of heated humidified gases up to 60 LPM (litres per minute) via a nasal cannula. Particles of oral/nasal fluid released by patients undergoing NHF therapy may pose a cross-infection risk, which is a potential concern for treating COVID-19 patients. Methods Liquid particles within the exhaled breath of healthy participants were measured with two protocols: (1) high speed camera imaging and counting exhaled particles under high magnification (6 participants) and (2) measuring the deposition of a chemical marker (riboflavin-5-monophosphate) at a distance of 100 and 500 mm on filter papers through which air was drawn (10 participants). The filter papers were assayed with HPLC. Breathing conditions tested included quiet (resting) breathing and vigorous breathing (which here means nasal snorting, voluntary coughing and voluntary sneezing). Unsupported (natural) breathing and NHF at 30 and 60 LPM were compared. Results Imaging: During quiet breathing, no particles were recorded with unsupported breathing or 30 LPM NHF (detection limit for single particles 33 μm). Particles were detected from 2 of 6 participants at 60 LPM quiet breathing at approximately 10% of the rate caused by unsupported vigorous breathing. Unsupported vigorous breathing released the greatest numbers of particles. Vigorous breathing with NHF at 60 LPM, released half the number of particles compared to vigorous breathing without NHF. Chemical marker tests: No oral/nasal fluid was detected in quiet breathing without NHF (detection limit 0.28 μL/m3). In quiet breathing with NHF at 60 LPM, small quantities were detected in 4 out of 29 quiet breathing tests, not exceeding 17 μL/m3. Vigorous breathing released 200–1000 times more fluid than the quiet breathing with NHF. The quantities detected in vigorous breathing were similar whether using NHF or not. Conclusion During quiet breathing, 60 LPM NHF therapy may cause oral/nasal fluid to be released as particles, at levels of tens of μL per cubic metre of air. Vigorous breathing (snort, cough or sneeze) releases 200 to 1000 times more oral/nasal fluid than quiet breathing (p < 0.001 with both imaging and chemical marker methods). During vigorous breathing, 60 LPM NHF therapy caused no statistically significant difference in the quantity of oral/nasal fluid released compared to unsupported breathing. NHF use does not increase the risk of dispersing infectious aerosols above the risk of unsupported vigorous breathing. Standard infection prevention and control measures should apply when dealing with a patient who has an acute respiratory infection, independent of which, if any, respiratory support is being used. Clinical trial registration ACTRN12614000924651

The effect of respiratory activity, non‐invasive respiratory support and facemasks on aerosol generation and its relevance to COVID‐19

“…generating procedures [17][18][19][20]. Patients acutely requiring HFNO or NIPPV are likely to present a high disease transmission risk due to their propensity to produce aerosols, but we find no basis for withholding or delaying access to these therapies.…”

Airway management in the adult patient with COVID-19: High flow nasal oxygen or not? A summary of evidence and local expert opinion

“…This increased particle count was significantly less than with BiPAP and nebulised oxygen (O 2 ) at 10 l/ min. Jermy et al 24 studied healthy participants during 'quiet breathing' and 'vigorous breathing' (i.e. coughing, snorting or sneezing) either unsupported or using HFNO.…”

“…The particle counter studies measure particles of differing sizes more similar to the full range of human respiratory aerosols, but again with different detection limits of 5 lm, 23 10 lm 25 and even 33 lm. 24 The studies showing growth of bacteria, or yeast dispersion at distances from the HFNO 33,34 may be indicative but cannot deliver direct conclusions about viral spread. The studies were performed in conditions with a range of air changes per hour (ACH) generally between six and 15 ACHs.…”

High-Flow Nasal Cannula Treatment in Patients with COVID-19 Acute Hypoxemic Respiratory Failure

“…[ 25 ] However, multiple studies generated a cumulative low-moderate quality of evidence, which indicate a relatively low risk of dispersing a significant amount of bio-aerosol particles and suggest no increase in the risk of infection transmission to healthcare workers with an excellent fitted HFNC, good sealing circuit, and appropriate adherence to airborne precautions. [ 26 25 24 25 26 27 28 29 30 31 ] Yet, high-quality evidence on the risk of airborne contamination and nosocomial infection with the use of HFNC for the management of COVID-19 patients is needed.…”