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Nitric oxide delivery during high-frequency oscillatory ventilation.

BACKGROUND
Inhaled nitric oxide (NO) is used increasingly in the care of infants with hypoxemic respiratory failure and is frequently combined with high-frequency oscillation (HFO). The aim of this study was to evaluate delivery of NO during HFO using titration into the ventilator circuit or using the INOvent Delivery System.


METHODS
NO was delivered into the HFO circuit at three sites (pre-humidifier, post-humidifier, and after the bellows) by continuous titration using a rotameter. The target NO concentration ([NO]) was initially adjusted using a rapid-response chemiluminescence NO analyzer without oscillation at 5, 10, and 20 parts per million (ppm). During the study, gas was sampled 5 cm from the bellows (proximal), 35 cm from the bellows (middle), and at the distal end of the circuit (distal). The ventilator was set at frequencies of 5, 10, and 15 Hz, mean airway pressures of 15, 20, and 25 cm H(2)O, and amplitudes of 20, 30, and 40 cm H(2)O. Soft and hard circuits were evaluated. The fraction of inspired oxygen was 0. 90, the inspiratory time fraction was 33%, and the bias flow was 20 L/min throughout the study. An INOvent Delivery System was also evaluated with the same HFO settings.


RESULTS
The fluctuation of [NO] was minimal with continuous titration pre-humidifier at all HFO settings. [NO] fluctuated with titration post-humidifier and after the bellows, especially at the proximal sampling site. At the lung model, however, fluctuation of [NO] was always < 1.5 ppm and usually < 1 ppm. Delivered [NO] was lower than target [NO] with injection after the bellows (> 5%). The soft circuit showed better mixing of NO than the hard circuit. The INOvent Delivery System delivered a stable and accurate [NO] at all settings. [NO(2)] was < 1 ppm at all settings.


CONCLUSIONS
Mixing of NO during HFO was acceptable at all the injection sites evaluated, although injection pre-humidifier was preferable because of small fluctuations of [NO]. The INOvent Delivery System was simple to use and delivered an accurate and precise [NO] during HFO.