High frequency oscillatory ventilation during spontaneous breathing

Slager, S. (2015) High frequency oscillatory ventilation during spontaneous breathing. thesis, Medicine.

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Abstract

Introduction Mechanical ventilation (MV) can be life saving in the treatment of respiratory failure, but can also cause ventilator-induced or -associated lung injury (VILI/VALI). High frequency oscillatory ventilation (HFOV) ventilates with tidal volumes (VT) smaller than in conventional lung protective ventilation (CV) and delivers a high continuous distending pressure (CDP), reducing risk of volutrauma and atelectrauma and consequently VILI/VALI. However, recent clinical trials found a higher mortality rate in patients on HFOV compared to patients on CV, which might have been caused by not using optimal recruitment strategies and ventilator settings. It is suggested that optimal HFO ventilator settings include high frequency and power settings (regulating amplitude of oscillations) instead of the lower frequency and power settings often used, as VT is lower in high frequency and power settings. Spontaneous breathing during MV, another important form of lung protection, allows more efficient use of the available lung tissue. Combining optimally set HFOV and spontaneous breathing would optimize lung protection. However, the effect of this combination on HFOV VT is unknown. This study was performed to test the hypothesis that using high frequency and power settings in HFOV still significantly reduces HFOV VT during spontaneous breathing and that HFOV VT remains lower than VT in CV. Materials and methods A series of experiments was performed on a test lung with simulated spontaneous breathing connected to an HFO 3100A ventilator (CareFusion, Yorba Linda, USA). Flow proximal to the endotracheal tube (ETT) and oscillator and test lung pressures were recorded for combinations of the following variables: frequencies 5, 10 and 15 Hz, power settings 50 – 100 in steps of 10, ETT sizes 3, 4, and 5 mm, bias flow 20 and 40 L/min, CDP 15, 25, and 35 cm H2O, and test lung compliance 5/50, 3/30, and 2/20 mL/cm H2O, volume of spontaneous breaths 5, 7, and 10 mL/kg. Using dedicated Matlab (v. 8.3) scripts, the mean HFOV VT and the mean pressure attenuation during spontaneous expiration were calculated. Regression analysis and comparisons of HFOV VT between different settings with Kruskal-Wallis tests and post-hoc analysis with Mann-Whitney U tests were performed with SPSS v. 22. Results Increasing frequency from 5 - 10 Hz (r = .64) and from 10 – 15 Hz (r = .42) significantly decreased HFOV VT. This VT decrease for frequency increase of 10-15 Hz lacked in some variable combinations with a compliant test lung and lower power settings. High frequency and power settings reduced the HFOV VT to a mean of 3.06 mL (SD = 0.31 mL), 4.57 mL (SD = 1.04 mL), and 8.15 mL (SD = 2.67 mL) for ETT size 3, 4, and 5 mm respectively, all considerably smaller than the VT resulting from CV at 6 mL/kg (21 mL, 60 mL, and 120 mL respectively). ETT size, frequency, power settings, volume of spontaneous breaths, bias flow, and CDP significantly contributed to HFOV VT. ETT size, frequency, volume of spontaneous breaths, and power settings were the main contributors. ETT size, CDP, and power settings were the main contributors to pressure attenuation; Conclusion This bench test convincingly shows that the use of higher frequency and power settings in HFOV during spontaneous breathing significantly reduces HFOV VT and that HFOV VT remains lower than VT in CV. Furthermore it shows that HFOV pressure attenuation differs between ETT sizes, which means it will differ between patients of different sizes, and that the pressure delivered to the lungs might not change the way that was intended when changing HFO ventilator settings.

Item Type:	Thesis (Thesis)
Supervisor name:	Supervisor: and Kneyber, Dr. M.C.J. and Department: Pediatric Intensive Care Unit, University Medica
Faculty:	Medical Sciences
Date Deposited:	25 Jun 2020 10:46
Last Modified:	25 Jun 2020 10:46
URI:	https://umcg.studenttheses.ub.rug.nl/id/eprint/758

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