Objective: Identify variables independently associated with delivered tidal volume (VT) and measured mean airway pressure during high-frequency oscillatory ventilation across the range of pediatric endotracheal tube sizes.
Design: In vitro study.
Setting: Research laboratory.
Interventions: An in vitro bench model of the intubated pediatric respiratory system during high-frequency oscillatory ventilation was used to obtain delivered VT and mean airway pressure (in the distal lung) for various endotracheal tube sizes. Measurements were taken at different combinations of ventilator set mean airway pressure (Paw), amplitude (ΔP), frequency, and test lung compliance. Multiple regression analysis was used to construct multivariable models predicting delivered VT and mean airway pressure.
Measurements and Main Results: Variables independently associated with higher delivered VT for all endotracheal tube sizes include higher ΔP (p < 0.001), lower frequency (p < 0.001), and higher test lung compliance (p < 0.001). A multiplicative interaction between frequency and ΔP magnifies the delivered VT when ΔP is high and frequency is low (p < 0.001). Delivered mean airway pressure becomes lower than set Paw as ΔP increases (p < 0.001) and frequency increases (p < 0.05). Ventilator set Paw is the largest determinant of delivered mean airway pressure; however, increasing ΔP resulted in a lower delivered mean airway pressure. For example, in a 4.0 mm ID endotracheal tube, increasing ΔP by 10 cm H2O resulted in an average decrease of delivered mean airway pressure by 4.5%.
Conclusions: This is the first study to quantify the interaction between ΔP and frequency in delivered VT and the effect of ΔP and frequency on delivered mean airway pressure. These results demonstrate the need to measure or estimate VT and delivered pressures during high-frequency oscillatory ventilation and may be useful in determining optimal strategies for lung protective ventilation during high-frequency oscillatory ventilation.
1Department of Anesthesiology and Critical Care Medicine, Children’s Hospital Los Angeles, Los Angeles, CA.
2Department of Pediatrics, Keck School of Medicine, University of Southern California, Los Angeles, CA.
3Department of Pediatric Critical Care, Geisinger Medical Center, Janet Weis Children's Hospital, Danville, PA.
This study was performed at Children’s Hospital Los Angeles, Los Angeles, CA and CareFusion, Yorba Linda, CA.
Supported, in part, by grants from Children’s Hospital Los Angeles and Anesthesia Critical Care Medicine Research Oversight Committee Fund.
Dr. Wong disclosed other support (some of the work was performed on site at CareFusion in Yorba Linda, CA). Dr. Deakers disclosed other support (CareFusion allowed authors access to certain equipment and space at their facility: test lung and pressure transducer). Dr. Khemani disclosed other support (CareFusion provided facilities to perform some of the research but no financial support was supplied) and received support for article research from CareFusion. The remaining authors have disclosed that they do not have any potential conflicts of interest.
Address requests for reprints to: Ronald Wong, DO, Geisinger Medical Center, Janet Weis Children’s Hospital, 100 N. Academy Avenue, M.C. 27-22, Danville, PA 17822. E-mail: email@example.com