The Science Journal of the American Association for Respiratory Care
Background: Passive humidifiers, such as hygroscopic condenser humidifiers (HCH) have been used increasingly in ventilator circuits since the mid-1980s. Because the HCH is placed between the patient wye and the ET tube, it would need to be removed from the circuit before an MDI drug could be delivered from a location on the inspiratory limb of the circuit. To avoid breaking the circuit for an MDI treatment, it would be desirable to place the MDI device between the HCH and the ET tube, as long as it could be shown that the MDI drug would not clog the HCH even under non-ideal conditions.
Method: A Bear 1 ventilator (VT = 700 mL, peak flow = 45 L/min, 6 breaths/min) was attached to a patient wye, which was followed by a Baxter Adult Filtered HCH, then a Thayer dual-spray 15-mm ID/OD MiniSpacer
Results: The graph shows the air flow resistance of the HCH (inches H2O) measured periodically during the 72-hour test and control. Error bars show the measurement uncertainty in the air flow resistance. Results for the 72-minute tests are not shown here but are similar: In no case did the HCH resistance change. The two-factor ANOVA showed statistical equivalence among all results with time.
Conclusions: MDI drugs delivered at the ET tube are unlikely to clog an HCH, even if the drug is somewhat sticky (like Alupent) and even if the MDI is actuated at the wrong part of the breath cycle. There are other reasons (dose output) to actuate the MDI at the start of inhalation, and there are other substances (secretions) that may clog an HCH, but the MDI drug is not implicated as a clogging agent even in the ?worst case.?
(See Original for Figure)