Assessment & mitigation of O2 therapy driven spread of COVID-19

Abstract

BACKGROUND: Exhalation exposure from patients to healthcare workers (HCWs), while using a nasal cannula or simple O2 mask used in treating COVID-19 and other respiratory diseases, is a present and future risk. Little is known on exhalation dispersal through these devices, and on mitigating the viral exposure to those in the vicinity. METHODS: Respiration through O2 therapy devices was studied with a supine manikin equipped with a controllable mechanical lung by measuring aerosol density and flow with direct imaging. Dispersal direction and distances were quantified while placing a surgical mask loosely over the devices and contrasted with unmitigated oxygenation device use. Exhalation jets were examined over the entire range of oxygenation rates used in treatment. RESULTS: Exhalation jets travel 0.35 plus/minus 0.02 m upward while wearing a nasal cannula, and 0.29 plus/minus 0.02 m laterally while wearing a simple O2 mask posing significant inhalation risk. Placing a surgical facemask loosely over the oxygenation device is demonstrated to alleviate exposure by reducing and deflecting the exhalation jets from being launched forward, and by reducing exhalations from being launched directly higher over a supine patient. Less than 12% of the exhaled breath is observed to reach above a masked face where HCWs would be present, independent of oxygen flow rates. CONCLUSIONS: Exhalation jets from both the nasal cannula or simple O2 mask were found to concentrate aerosol-laden exhalations directly in front of a patient's face. Exposure is effectively mitigated with a surgical mask which reduces and redirects the exhalation downward away from HCWs.

Exhaled patient derived aerosol dispersion during awake tracheal intubation with concurrent high flow nasal therapy

“…Figure 3 shows the distribution of exhaled aerosol particles, in terms of relative quantities (#), above and below a threshold of 5 µm in diameter in the operating room at the different positions and supplemental air flow rates. This threshold was chosen as it has been documented in the literature that aerosol particles < 5 µm in diameter carry the highest risk of inhalation and airborne transmission of viral loads [19][20][21]. The greatest number of potentially respirable particles, < 5 µm, remained entrained in the jet of exhaled aerosol, peak of 9211 particles at 0.5 m and 0° from the subject midline at 50 LPM.…”

“…These distances are considerably less than our observations. The majority of other studies in the literature that examine the dispersion of aerosol particles during a particular aerosol treatment provide either a 2D visualisation or a single point measurement, [19][20][21]. The data presented in Figs.…”

Exhaled Patient Derived Aerosol Dispersion during Awake Tracheal Intubation with Concurrent High Flow Nasal Therapy

“…Figure 3 shows the distribution of exhaled aerosol particles, in terms of relative quantities (#), above and below a threshold of 5 µm in diameter in the operating room at the different positions and supplemental air ow rates. This threshold was chosen as it has been documented in the literature that aerosol particles < 5 µm in diameter carry the highest risk of inhalation and airborne transmission of viral loads [19][20][21]. The greatest number of potentially respirable particles, < 5 µm, remained entrained in the jet of exhaled aerosol, peak of 9211 particles at 0.5 m and 0° from the subject midline at 50 LPM.…”