The Science Journal of the American Association for Respiratory Care

1996 OPEN FORUM Abstracts

Five Things I Learned this Year about Nitric Oxide

Ray Ritz, RRT Sunday, November 3, 1996

As we have gained experience with the administration of nitric oxide, a more organized and less mysterious approach has been developed. Our most recent improvements in this therapy include:

1. Concentrations: Higher concentrations of nitric oxide - those in excess of 20 ppm offer little if any benefit to patients presenting with hypoxemia and/or pulmonary hypertension. Preliminary data actually implies that hypoxemic patients PaO_{2}'s are statistically better at 5 ppm than at 20 ppm. Additionally, lower concentrations offer the obvious benefit of lower risk of inadvertent exposure to NO_{2} and the development of methemoglobin anemia. This current information may indicate that for most clinical situations, NO levels do not need to exceed 20 ppm and less may be better.

2. Weaning: We have developed a safe efficient method to wean NO during mechanical ventilation. Since low concentrations of NO appear to present little risk, after initiating a NO dose of 5 - 20 ppm, we give priority to reducing ventilatory support over reducing the NO level. Once the patient's lung function improves as is evidenced by PEEP requirements of < 10 cm H_{2}O and the FiO_{2} requirements of < 0.50, the FiO_{2} is increased by at least 20% and the NO is discontinued. The FiO_{2} is then reduced as tolerated based on the monitored SpO_{2}.

3. Scavenging: A standard ICU room ventilation system changes the entire room air supply approximately 6 times per hour. When administering NO during mechanical ventilation levels between 5 and 80 ppm and at minute ventilation's between 1 and 20 l/m, we have not seen ambient concentrations on NO rise more than 50 - 60 ppb above normal background levels. With this data, we have discontinued attempting to scavenging exhaled NO.

4. Delivery Techniques Systems to deliver NO during mechanical ventilation in both adults and pediatric settings should conform to certain basic standards. The delivered concentrations should be stable through out the inspiratory cycle. During non-constant flow, this requires pre-mixing the NO into the ventilator compressed gas sources. Titrating No into a non-constant gas flow will result in large fluctuations in NO levels. Delivery systems should be designed in a way to avoid inadvertent development of nitrogen dioxide. The use of nitrogen (N_{2}) instead of compressed air as a carrier gas may be needed for some ventilatory conditions.

5. Analyzers The limitations of NO and NO_{2} analyzers should be understood. Both electrochemical and chemiluminesence analyzers generally have minimum response times of 30 and 6 seconds respectively. This means that neither technology will monitor fluctuations in NO levels during a single breath. Since the therapeutic levels of NO that are most commonly used are between 5 and 20 ppm, the need for chemiluminesence devices, with their relative high cost, is questionable outside of specific research applications.

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