1999 OPEN FORUM Abstracts

NITRIC OXIDE DELIVERY DURING HIGH FREQUENCY OSCILLATION (HFO).

Yuji Fujino, MD, Robert M Kacmarek, PhD RRT FAARC, Dean Hess, PhD RRT FAARC. Departments of Respiratory Care and Anaesthesia, Massachusetts General Hospital and Harvard Medical School, Boston MA.

Background: We have previously investigated the fluctuation of nitric oxide concentration ([NO]) during inhaled NO therapy with conventional mechanical ventilation (Anesthesiology 1997; 86:676 and Chest 1998; 133:1650-1657). However, no study has reported the accuracy of NO delivery during HFO to determine whether [NO] fluctuates beyond the clinically acceptable range. The aim of this study was to evaluate the mixing of NO titrated into the HFO ventilator circuit at different sites using a rapid response [NO] analyzer. Method: An oscillator (Sensormedics 3100A, Yorma Linda CA) was set up in the usual manner to ventilate a test lung (compliance »1 mL/cm H₂O). NO (800 ppm) was titrated into the circuit pre-humidifier, posthumidifier, and after the bellows. Target [NO] was adjusted using a calibrated rapid response analyzer (Sievers NOA 280, Boulder CO) without oscillation at 5, 10, 20 ppm. The ventilator was set at FIO₂ 0.9, inspiratory fraction 33%, bias flow of 20 L/min, and all combinations of frequency 5, 10, 15 Hz; mean airway pressure 15, 20, 25 cm H₂O; and amplitude 20, 30, 40 cmH₂O. Gas was sampled and [NO] measured with the rapid response analyzer either 5 cm from the bellows (proximal), 35 cm from the bellows (mid), or at the distal end of the circuit (distal). The INOvent Delivery System (Datex-Ohmeda, Madison WI) was evaluated in a similar manner (prehumidifier injection site only). [NO₂] was measured with a calibrated electrochemical cell (INOvent).

Results: The figure shows target [NO] of 20 ppm, frequency 10 Hz, and mean airway pressure 20 cm H₂O (closed bars for proximal sampling, gray bars for mid-sampling, and open bars for distal sampling). With NO injection after the bellows, the delivered [NO] at the mid and distal sampling sites was lower than target [NO] (> 5%). The INOvent delivered virtually the target [NO] at all conditions. The [NO₂] was <1 ppm for all settings.

Conclusions: Mixing of NO was satisfactory, particularly when NO was titrated into the circuit before the humidifier. Comparable results occurred with the INOvent and titration of NO into the circuit. The levels of NO₂ were low and acceptable.

(See Original for Figure)

OF-99-120