Experimental conditions

The following common airway management procedures were studied:

Non-invasive CPAP with PEEP (positive end expiratory pressure) of 5 mbar, 6 mbar, 8 mbar and 10 mbar with and without coughing

Non-invasive CPAP with a PEEP of 5 mbar and a Δp support (pressure support ventilation) of 10 mbar, 15 mbar and 20 mbar with and without coughing

Non-invasive CPAP without leakage, with 50% leakage and with 80% leakage with and without coughing

Nasal oxygen via a nasal tube (Dahlhausen, Köln, Germany) at 2 l/min, 4 l/min, 6 l/min, 8 l/min and 10 l/min with and without coughing

High-flow nasal oxygen at 15 l/min without coughing

Nebulizing with an oxygen mask (Micro Mist Nebulizer plus mask, Hudson RCI, Wayne, PA, USA)

Tracheal cannula suctioning with (7.1) and without (7.2) filter (Hygroscopic Condenser Humidifier, Aqua + TS, Hudson RCI, Wayne, PA, USA)

Tracheal cannula removal without filter

Coughing and suctioning after tracheal cannula removal

Reinsertion of tracheal cannula without filter

Extubation (5.0 no cuff Vygon, Aachen, Germany)

SARS CoV-2 swab according to the WHO (World Health Organization) guidelines²⁴.

For procedure (1) to (3), a Dräger Evita V800 respirator (Lübeck, Germany) was used. For procedures (7) to (10), a Tracheoflex, 9,0 mm, with Cuff (Rüsch, Berlin, Germany) was applied. The nebulizing therapy was used for representation of fine particle aerosols (manufacturer´s information mass median aerodynamic diameter (MMAD) 3.6 µm).

Additionally, the procedure speaking “stay healthy” was used as positive control (13).