Introduction: Aerosol therapy is often delivered concurrently during high flow nasal oxygen therapy (HFNO). HFNO system settings and design, including nasal cannula, have a significant impact on aerosol delivery. Recently, new cannula designs have combined one large and one small diameter nare to increase the velocity of the incoming gas for more efficient CO2 clearance. However, the effect of this design on the quantity of aerosol available for inhalation is unknown. The objective of this study was to assess the quantity of aerosol available at the exit of a new asymmetric nasal cannula compared to the current symmetric nasal cannula.    

Methods: 2000µg salbutamol was nebulised using the Aerogen Solo nebuliser and Pro-X controller in conjunction with the Airvo 2 (F&P, NZ) high flow system. Four adult nasal cannula types were tested, the F&P Optiflow+944 and 946 (symmetrical) and the Optiflow+964 and 966 (asymmetrical). The aerosol available exiting the nares was measured at 30, 50 & 60LPM using UV-spectrophotometry at 276nm. Paired T-tests determined statistically significant differences.  

Results: Table 1. Comparison of aerosol avaiable at the exit of different nares.

*Denotes asymmetric cannula design. P>0.05  for all tests

Conclusions: The new asymmetrical Optiflow nasal cannula did not have a significant effect on the amount of aerosol available for inhalation over current symmetrical Optiflow cannula designs.