The Science Journal of the American Association for Respiratory Care
Background: Bronchodilators are commonly administered through small volume nebulizers (SVN) placed in-line with a high flow oxygen source. It is unknown how efficient SVN therapy is when given in this manner. This study was designed to determine the efficacy of SVN treatments when given in-line with high flow oxygen to spontaneously breathing patients.
Methods: A 2-chamber test lung connected by a metal bar had one side driven by a ventilator to simulate spontaneous breathing parameters of 500 mL tidal volume and 20 breaths per minute. An aerosol mask was adapted to fit a filter connected to the ?patient? chamber of the test lung. Prepared salbutamol sulphate (5mg in 5mL) was nebulized from a SVN connected directly to the aerosol mask using a driving flow of 8 L/min oxygen. The treatment ran until no audible or visible nebulization occurred for 30 seconds. The test was run at the two patient inspiratory flows (40 and 80 L/min) and then repeated with the SVN placed in-line with high flow oxygen sources at 36 and 70 L/min corresponding to FiO2's of 0.40 and 0.70 respectively. Aerosol was captured by the filter and then analyzed using a spectrophotometer (280 nm). Absorbance was determined using a standard solution of salbutamol sulphate with a concentration of 0.04 mg/mL.
Results: Mean concentration of salbutamol (±SD) deposited on the filters is recorded in the table below.
|Patient inspiratory flow||SVN alone||36 L/min (FiO2 = 0.40)||70 L/min (FiO2 = 0.70)|
|40 L/min||*1.23±0.01 mg||?0.37±0.01 mg||?0.15±0.04 mg|
|80 L/min||1.13±0.03 mg||?0.36±0.07 mg||ND|
|*p < 0.01 vs 80 L/min, ?p < 0.0001 vs SVN alone, ?p < 0.005 vs SVN alone. ND - not done.|
Conclusions: High flow oxygen drastically reduces the amount of drug delivered by an in-line SVN to approximately 2%! Therefore, this practice should be abandoned immediately. Alternate therapies could include a SVN with an oxygen reservoir bag or the use of an MDI.