• Craig D Smallwood, Kevin J Bullock, and Andrew Gouldstone.
• Division of Critical Care Medicine, Department of Anesthesiology, Perioperative and Pain Medicine, Boston Children's Hospital, Boston, MA; Department of Bioengineering, Northeastern University, Boston, MA; Harvard Medical School, Boston, MA. Electronic address: craig.smallwood@childrens.harvard.edu.
• J Crit Care. 2016 Aug 1; 34: 142-5.

PurposeHigh-frequency airway clearance therapy is a positive pressure secretion clearance modality used in pediatric and adult applications. However, pressure attenuation across different size endotracheal tubes (ETT) has not been adequately described. This study quantifies attenuation in an in vitro model.Materials And MethodsThe MetaNeb® System was used to deliver high-frequency pressure pulses to 3.0, 4.0, 6.0 and 8.0mm ID ETTs connected to a test lung during mechanical ventilation. The experimental setup included a 3D-printed trachea model and imbedded pressure sensors. The pressure attenuation (Patt%) was calculated: Patt%=[(Pproximal-Pdistal)/Pproximal]x100. The effect of pulse frequency on Pdistal and Pproximal was quantified.ResultsPatt% was inversely and linearly related to ETT ID and (y=-7.924x+74.36; R(2)=0.9917, P=.0042 for 4.0Hz pulse frequency and y=-7.382+9.445, R(2)=0.9964, P=.0018 for 3.0Hz pulse frequency). Patt% across the 3.0, 4.0, 6.0 and 8.0mm I.D. ETTs was 48.88±10.25%, 40.87±5.22%, 27.97±5.29%, and 9.90±1.9% respectively. Selecting the 4.0Hz frequency mode demonstrated higher Pproximal and Pdistal compared to the 3.0Hz frequency mode (P=.0049 and P=.0065). Observed Pdistal was <30cmH2O for all experiments.ConclusionsIn an in vitro model, pressure attenuation was linearly related to the inner diameter of the endotracheal tube; with decreasing attenuation as the ETT size increased.Copyright © 2016 Elsevier Inc. All rights reserved.

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