PURPOSE: To visually illustrate and compare the various types of gas characteristics as tidal and sub-tidal breaths are introduced in a lung compartment model from four modes of ventilation; conventional mechanical ventilation (CMV), Bivent, HFOV and HFPV. This study may also offer clues as to how gas behaves when introduced in non-compliant compartments of the lung. We have no knowledge of a similar test conducted to visually illustrate the characteristics of gas as it is delivered in a lung compartment model.
METHODS: A lung compartment model comprising of a standard 1 liter test lung 190 (60 06 832 E037E) is wyed together with a 750 ml transparent glass bottle. The test lung 190 represents the compliant compartment while the glass bottle represents the non-compliant compartment. The bottle is filled with foam packaging peanuts (FPP) to represent movement of gas as tidal and sub-tidal breaths that are delivered when attached to four modes of ventilation. Ventilator parameters from each mode of ventilation was set to reflect similar peak inspiratory pressure (PIP) (35 cmH2O) and peak airway pressure (Paw) (25 cmH2O) and 500 cycles per minute for both HFOV and HFPV. Movement of the FPP will be observed as gas is introduced from each individual mode of ventilation.
RESULTS: As a breath was introduced in the lung compartment model, each mode of ventilation showed significant difference in movement of the FPP. There was no movement of FPP during CMV and Bivent as breaths were delivered. In HFOV, turbulent movement of the FPP was noted and magnitude varied with increasing amplitude (ΔP). Turbulent movement of FPP was also noted with every HFPV delivered breath. Additionally, particles of FPP appear to flow out of the test lung compartment during HFOV and HFPV. This could reflect active movement of gas from the lung compartment during HFOV and HFPV.
CONCLUSIONS: Gas characteristics varied significantly between the modes of ventilation. The visible movement of the FPP in HFOV and HFPV is evidence of the existing turbulent flow produced by the HFOV diaphragm and sliding venturi of the HFPV Phasitron. This visible movement of gas which potentially results in improved oxygenation and ventilation may be the reason why lower pressures are needed during HFOV and HFPV ventilation.
CLINICAL IMPLICATIONS: The visual demonstration of these gas characteristics may offer clues to why oxygenation and ventilation are readily accomplished when patients are transitioned to HFOV or HFPV.
DISCLOSURE: The following authors have nothing to disclose: Fariborz Rezai, Robert Tero, Linda Melchor
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