Effect of Heat Moisture Exchanger on Aerosol Drug Delivery and Airway Resistance in Simulated Ventilator-Dependent...

Placement of a heat moisture exchanger (HME) between aerosol generator and patient has been associated with greatly reduced drug delivery. The purpose of this study was to evaluate the effect of filtered and nonfiltered HMEs placed between nebulizer and patient on aerosol deposition and airway resistance (Raw) in simulated ventilator-dependent adults.

An in vitro lung model was developed to simulate a mechanically ventilated adult (Vt 500 mL, RR 15/min, and PEEP 5 cmH₂O, using two inspiratory flow rates 40 and 50 L/min) using an intubated adult manikin with an endotracheal tube (8 mmID). The bronchi of the manikin were connected to a Y-adapter through a collecting filter (Respirgard II) attached to a test lung through a heated humidifier (37°C producing 100% relative humidity) to simulate exhaled humidity. For treatment conditions, a nonfiltered HME (ThermoFlo™ 6070; ARC Medical) and filtered HMEs (ThermoFlo™ Filter; ARC Medical and PALL Ultipor; Pall Medical) were placed between the ventilator circuit at the endotracheal tube and allowed to acclimate to the exhaled heat and humidity for 30 minutes before aerosol administration. Airway resistance (cmH₂O/L/s) was taken at 0, 10, 20, and 30 minutes after HME placement and after each of four aerosol treatments. Albuterol sulfate (2.5 mg/3 mL) was administered with jet (Misty Max 10; Airlife) and mesh (Aerogen Solo; Aerogen) nebulizers positioned in the inspiratory limb proximal to the Y-adapter. Control consisted of nebulization with no HME. Drug was eluted from filter at the end of the trachea and measured using spectrophotometry (276 nm).

Greater than 60% of the control dose was delivered through the ThermoFlo. No significant difference was found between the first four treatments given by the jet (p = 0.825) and the mesh (p = 0.753) nebulizers. There is a small increase in Raw between pre- and post-four treatments with the jet (p = 0.001) and mesh (p = 0.015) nebulizers. Aerosol delivery through filtered HMEs was similar (<0.5%) across the four treatments. Airway resistance was similar using the ThermoFlo Filter. With the PALL Ultipor, changes in Raw increased with mesh nebulizer after treatment (p = 0.005). Changes in resistance pre- and post-treatment were similar with both filtered HMEs.

The ThermoFlo™ nonfilter HME allowed the majority of the control dose to be delivered to the airway. Increases in Raw would likely not be outside of a tolerable range in ventilated patients. In contrast, filtered HMEs should not be placed between nebulizers and patient airways. Further research with other HMEs and materials is warranted.