Humidification during high-frequency oscillation ventilation is affected by ventilator circuit and ventilatory setting.
BACKGROUND
High-frequency oscillation ventilation (HFOV) is an accepted ventilatory mode for acute respiratory failure in neonates. As conventional mechanical ventilation, inspiratory gas humidification is essential. However, humidification during HFOV has not been clarified. In this bench study, we evaluated humidification during HFOV in the open circumstance of ICU. Our hypothesis is that humidification during HFOV is affected by circuit design and ventilatory settings.


METHODS
We connected a ventilator with HFOV mode to a neonatal lung model that was placed in an infant incubator set at 37 degrees C. We set a heated humidifier (Fisher & Paykel) to obtain 37 degrees C at the chamber outlet and 40 degrees C at the distal temperature probe. We measured absolute humidity and temperature at the Y-piece using a rapid-response hygrometer. We evaluated two types of ventilator circuit: a circuit with inner heating wire and another with embedded heating element. In addition, we evaluated three lengths of the inspiratory limb, three stroke volumes, three frequencies, and three mean airway pressures.


RESULTS
The circuit with embedded heating element provided significantly higher absolute humidity and temperature than one with inner heating wire. As an extended tube lacking a heating wire was shorter, absolute humidity and temperature became higher. In the circuit with inner heating wire, absolute humidity and temperature increased as stroke volume increased.


CONCLUSIONS
Humidification during HFOV is affected by circuit design and ventilatory settings.
Chikata
Yusuke
Y
Department of Emergency and Critical Care Medicine, The University of Tokushima Graduate School, Tokushima 770-8503, Japan.
Imanaka
Hideaki
H
Onishi
Yoshiaki
Y
Ueta
Masahiko
M
Nishimura
Masaji
M
D006361:Heating / Q000379:methods; D006612:High-Frequency Ventilation / Q000295:instrumentation* / Q000379:methods; D006801:Humans; D006813:Humidity; D007231:Infant, Newborn; D001239:Inhalation; D015931:Intensive Care, Neonatal / Q000379:methods*; D012131:Respiratory Insufficiency / Q000628:therapy*; D013696:Temperature; D012122:Ventilators, Mechanical / Q000592:standards*