Pressure Attenuation During High-Frequency Jet Ventilation: An In Vitro Study

Abstract

Background:

High-frequency jet ventilation (HFJV) is commonly used for premature infants with respiratory failure. However, pressure attenuation across different HFJV settings and endotracheal tubes (ETT) has not been adequately described. Therefore, we sought to investigate and quantify pressure attenuation utilizing an in vitro model.

Methods:

The HFJV ventilator was configured in tandem with the conventional ventilator and connected to an ASL 5000 lung model. The lung model was used to simulate four infant scenarios (weight 0.5, 1, 2, and 4kg) with corresponding ETT ID (2.5, 3.0, 3.5 and 4.0 mm), respiratory compliance (0.5, 1, 2 and 5 mL/cm H₂O/kg) and resistance (50 to 200 cm H₂O/L/s). The conventional ventilator was controlled throughout experiment on PC-IMV, PIP 20 cm H₂O, PEEP 10 cm H₂O, frequency 2 (breaths/min), T_I 0.5 seconds and FIO₂ 0.21. Measurements were taken at combinations of HFJV PIP (20, 30 and 40 cm H₂O) inspiratory time (0.02, 0.026 and 0.034 ms), frequency (360 and 420 breaths/min) which were applied to all lung model and corresponding ETTs. Pproximal was measured at the LifePort ETT adapter and Pdistal via the pressure sensor embedded within 3-D printed neonatal trachea model, precisely at the ETT outlet. For each combination of settings 1-minute of pressure samples were recorded at 100 Hz. Pressure attenuation (Patt%) was calculated as: Patt% = [(Pproximal - Pdistal)/ Pproximal] x100. Patt% was quantified for each simulated infant scenario. Linear regression analysis was utilized to quantify the relationship between Patt% and Pproximal.

Results:

Patt% was linearly related to Pproximal (y = 1.285 + 27.249; R2 = 0.950, P <0.001) for all combinations of HFJV PIP. Mean Patt % at HFJV PIP of 20, 30 and 40 cm H₂O was 45.66 ± 15.24%, 62.73 ± 11.97% and 71.36 ± 14.56%, respectively.

Conclusions:

In an in vitro model, pressure attenuation was linearly related to Pproximal, with attenuation increasing as the HFJV PIP was increased.

Figure 1. Linear regression analysis of P_att % versus P_proximal, stratified by ETT ID.