A quantitative evaluation of aerosol generation during manual facemask ventilation

Shrimpton, A. J.; Brown, J. M.; Gregson, F. K. A.; Cook, T. M.; Scott, D. A.; Mcgain, F.; Humphries, R. S.; Dhillon, R. S.; Bzdek, B. R.; Hamilton, F.; Reid, J. P.; Pickering, A. E.; Group, AERATOR

Manual facemask ventilation, a core component of elective and emergency airway management, is classified as an aerosol generating procedure. This designation is based on a single epidemiological study suggesting an association between facemask ventilation and transmission from the SARS 2003 outbreak. There is no direct evidence to indicate whether facemask ventilation is a high-risk procedure for aerosol generation. We conducted aerosol monitoring during routine facemask ventilation, and facemask ventilation with an intentionally generated leak, in anaesthetised patients with neuromuscular blockade. Recordings were made in ultraclean theatres and compared against the aerosol generated by the patient during their own tidal breathing and coughs. Respiratory aerosol from tidal breathing was reliably detected above the very low background particle concentrations (191 (77-486 [3.8-1313]) versus 2.1 (0.7-4.6 [0-12.9] particles/L median(IQR)[range], n=11, p=0.002). The average aerosol concentration detected during facemask ventilation both without a leak (3.0 particles/L (0-9 [0-43])) and with an intentional leak (11 particles/L (7.0 - 26 [1-62])) was 64-fold and 17-fold lower than that of tidal breathing (p=0.001 and p=0.002 respectively). The peak particle concentration during facemask ventilation both without a leak (60 particles/L (0 - 60 [0-120])) and with a leak (120 particles/L (60 - 180 [60-480]) were respectively 20-fold and 10-fold lower than a cough (1260 particles/L (800 - 3242 [100-3682]), p=0.002 and p=0.001 respectively). This study demonstrates that facemask ventilation, even performed with an intentional leak, does not generate high levels of bioaerosol. On the basis of this evidence, facemask ventilation should not be considered an aerosol generating procedure.