1996 OPEN FORUM Abstracts
EVALUATION OF NITRIC OXIDE DELIVERY SYSTEMS FOR ADULT MECHANICAL VENTILATION.
Hideaki Imanaka, MD, Dean Hess, PhD, RRT, Max Kirmse, MD, Luca M. Bigatello, MD, Robert M. Kacmarek, PhD, RRT, Wolfgang Steudel, MD, william E. Hurford, MD. Respiratory Care and Department of Anesthesia, Harvard Medical School, Massachusetts General Hospital, Boston.
Various systems to administer inhaled nitric oxide (NO) have been used in patients and experimental animals. We have hypothesized that the NO dose is affected by the design of the delivery system, the response time of the analyzer, and the sample site. We useda lung model to evaluate five NO delivery systems during mechanical ventilation with a variety of ventilatory patterns. Methods: An adult mechanical ventilator (7200ae, Nellcor-Puritan- Bennett) was attached to a test lung (model 1600, Michigan Instruments) configured to separate inspired and expired gases. Four injection systems were evaluated with NO injected either into the inspiratory circuit 90 cm proximal to the Y-piece or directly at the Y-piece, and delivered either continuously or only during the inspiratory phase. Alternatively, NO was mixed with air using a blender (Bird/3M) and delivered to the high-pressure air inlet of the ventilator. NO concentration ([NO]) was measured from the inspiratory limb of the ventilator circuit and the tracheal level using rapid (280NOA, Sievers) and slow (CLD700AL,Eco Physics) response chemiluminescence analyzers. The ventilator was set for constant-flow volume control ventilation, pressure control ventilation (PCV), spontaneous breathing with pressure support ventilation or synchronized intermittent mandatory ventilation. Tidal volumes of 0.5 L and 1 L were evaluated with inspiratory times of 1 s and 2 s. Results: The system that premixed NO proximal to the ventilator was the only one that maintained constant NO delivery regardless of the ventilatory pattern. The other systems delivered variable [NO] during PCV and spontaneous breathing modes. Systems that injected a continuous flow of NO delivered peak [NO] greater than the calculated dose. [NO] measured at the tracheal level is shown below with PCV, tidal volume 0.5 L, inspiratory time 1 s, and target [NO] 20 ppm. These variations were not apparent when a slow response analyzer was used (thin lines). Conclusions: NO delivery systems which inject NO at a constant rate, either continuously or during inspiration only, into the inspiratory limb of the ventilator circuit produce highly variable and unpredictable [NO] when inspiratory flow is not constant. Such systems may deliver a very high [NO] to the lungs which is not accurately reflected by measurements performed with slow response analyzers.
See Original for figure.