The Science Journal of the American Association for Respiratory Care

2008 OPEN FORUM Abstracts


Norm Tiffin1, Kathy A. Short2, William J. Hanson2, Bruce A. Cairns2, Samuel W. Jones2

Introduction: High frequency percussive ventilation (HFPV) delivers intrapulmonary percussion to efficiently mobilize secretions at the same time providing for a lung protective strategy mode of ventilation. It has been used since the 1980s primarily for ventilation of patients with severe inhalational injury. However, there is little data on levels of humidification during HFPV. The purpose of this study was to measure and compare humidification from two humidifier systems during HFPV including a new humidifier technology, the Hydrate OMNI.

Methods: The VDR-4® ventilator (Percussionaire Corp., Sandpoint, Idaho) was set at PIP = 30 cm H2O, PEEP = 5 cm H2O, phase = 12 bpm; percussion rate = 600 bpm. Total flow was 20 L/min with neb flow set to deliver 12 L/min as measured by electronic flowmeter (PTS 2000, TSI Incorporated. Gas temperature and relative humidity were measured using an electronic hygrometer/thermometer (SHT75, Sensirion) between the patient wye and test lung. Relative humidity of the source gas was <3%. Ambient temperature was 24.8°C and RH was 47%. The Hydrate OMNI was set at 37°C, with a pump speed of 1.2 mg/min and inserted into the inspiratory limb of the circuit immediately proximal to the patient wye. The ConchaTherm IV was set at 37°C and "+2" and used a dedicated heated wire circuit. For the dual Neptune humidifier setup the second humidifier was placed in the nebulizer flow line proximal to the moving valve and set similar to above.Absolute humidity was calculated using a standard equation from temperature and RH.

Results: Results are given as mean (sd). AH is the mean for all measurements over the 10 minute period.

Conclusion: Anecdotal accounts of poor humidification during high frequency percussive ventilation are frequent and some clinicians limit the use of this mode of ventilation for this reason. This study shows that the Teleflex Neptune humidifier provides less than the acceptable minimum humidity levels. AARC Guideline for minimum absolute humidity for mechanical ventilation is 30 mg of H2O per liter of gas while ASTM and ISO standards require humidity levels no less than at 33 mg/L. The Hydrate OMNI provided absolute humidity levels well over both standards at 38.2 mg/L.

Further study with other humidifiers is required.