Bench Evaluation of Ventilator Mode Changes During High Frequency Jet Ventilation and Inhaled Nitric Oxide

Abstract

Background: High frequency jet ventilation (HFJV), conventional ventilation (CV), and inhaled nitric oxide (INO) are therapies that are often used simultaneously. In our Level IV NICU, we noticed a discrepancy between CV set PEEP (actual PEEP), Pmin, and measured PEEP on HFJV when CV modes were changed. We aimed to evaluate the effect of this discrepancy on the delivery of INO.

Methods: A Drager Babylog equipped with a F&P Evaqua 2 circuit interfaced a Bunnell LifePulse HFJV, INO was placed in-line (between gas outlet and heater) on the HFJV from a Mallinckrodt INOmax DSIR system to a Drager neonate test lung. Two models were evaluated, Model 1 included CV-PC CMV, PIP 25, Ti 0.35, RR 5, PEEP 6, HFJV- PIP 30, RR 420, Ti 0.02 and INO at 20 ppm (sampling post ETT and within the test lung). Model 2 included CV- SPN CPAP, PEEP 6, PS 6, with the HFJV and INO unchanged. Variables for analysis included: CV measured PEEP/Pmin, HFJV measured PEEP/ΔP and INO sampling on DSIR. Due to an observed decrease in PEEP and increase in ΔP on the HFJV when switching between models slightly larger V_Ts would be expected. INO sampling was obtained from within the test lung to evaluate INO delivery and values were obtained three times in each model after stabilization and averaged. Student’s t-test was used to determine statistical significance.

Results: Average values in CMV PC mode were CV PEEP 6.2, Pmin 5.9, HFJV PEEP 6.1, HFJV ΔP 23.9, INO 19 ppm. Average values in SPN CPAP mode were CV PEEP 5.8, Pmin 5.2, HFJV PEEP 5.3, HFJV ΔP 24.7, INO 19 ppm. Pmin/HFJV PEEP is decreased and HFJV ΔP is increased when CV mode is changed from CMV PC to SPN CPAP. As PEEP decreases and ΔP increases, larger V_Ts are expected. All reported pressure fluctuations were determined not significant (Table 1) and fall within manufacturer's specifications. INO delivery was not affected when CV mode changes were made when used in conjunction with HFJV.

Conclusions: Despite variability in CV Set PEEP, Pmin, and measured PEEP between CV and HFJV, when CV modes were changed INO delivery remained stable in our bench model. Further research must be done to evaluate expected volume increases and the potential impact to neonatal patients on these therapies.