Nitrogen dioxide measurement in breathing systems

Inhaled nitric oxide therapy in neonatal hypoxic respiratory failure: insights beyond primary outcomes

The Neonatal Research Network developed and initiated 3 multicenter randomized controlled clinical trials evaluating inhaled nitric oxide therapy. Additional projects evolved from these efforts including basic science research and observational investigations. This article provides a historical prospective of the Network's investigations related to the diagnosis and management of neonatal hypoxic respiratory failure, especially those related to inhaled nitric oxide therapy. It will review the Network's contributions toward advancing the clinical care of the newborn with severe hypoxic respiratory failure.

Improving accuracy of the chemiluminescent analyser for measurement of nitric oxide and nitrogen dioxide in respired gas

OBJECTIVE

The aim of this study was to improve the accuracy of the chemiluminescent analyser in the measurement of nitric oxide (NO) and nitrogen dioxide (NO2) in both dry and humidified gas mixtures containing oxygen (O2) in varying concentrations. This work was performed because initial attempts to determine rate constants for the decay of NO and rates of formation of NO2 were unsuccessful.

METHODS

Equations were developed by which the raw output signal of the analyser could be corrected for errors arising from variations in sensitivity of the analysis cell, degree of conversion of NO2 to NO and degradation of NO to nitrogen (N2) in the converter prior to analysis. Once correction factors were derived from calibration, the analyser was used to measure rate of decay of 40 ppm nitric oxide in both dry and humidified gases containing either 21%, 60% or 100% O2 in N2.

RESULTS

Correction factors obtained from calibration corrected falls in sensitivity to a maximum of 28%, variations in degree of conversion of NO2 to NO from 62-96% and degradation of NO from 2-8% in the converter before analysis depending on O2 concentration and humidification. When the calibrated machine was used to measure decay of NO, an excellent fit (r2 > 0.95) with a hyperbolic function was obtained confirming that rate of decay is proportional to oxygen O2 concentration and square of NO concentration. A rate constant per unit O2 concentration of 9.40E-10 ppm(-2) min(-1) for humidified gas was significantly higher than 8.27E-10 ppm(-2) min(-1) for "dry" gas (P = 0.008) at 22 degrees C. Rise in NO2 predicted from the "wet" rate constant achieved 3ppm in 65 seconds with 40 ppm NO in 100% oxygen and 107 sec. in 60% oxygen.

CONCLUSION

This study indicates that for accurate analysis of NO and NO2 concentrations in airway gases a rigorous calibration of the instrument for the conditions applying in the experiment is mandatory. Once this is achieved the instrument is capable of precise analysis of both gases.

Direct determination of trace nitrogen dioxide by atmospheric pressure lonization mass spectrometry (APIMS) without conversion to nitric oxide

The aim of this study was to develop a new method for the determination of NO(2) levels encountered in clinical settings as well as in environmental studies, using a bi-component atmospheric pressure ionization mass spectrometry (APIMS). Hydrogen (1%) diluted in pure argon was ionized by corona discharge in the first ionization component. Fifty ml of the analyte diluted in 250 ml of composite air or carbon dioxide (CO2) was introduced into the second ionization component and analyzed. When composite air was used as the sample carrier gas, NO in the analyte was oxygenated and there was an increase in the NO(2) content from that in the original analyte. However, when CO(2) was used as the sample carrier gas, the level of NO(2) in the analyte could be determined because CO(2) did not change the NO(2) content from that in the original analyte. A calibration curve with good linearity was obtained using the UG-410 APIMS system, with a regression equation of Y(%) = 5.513*10(-2) X (ppb) and a detection limit of 0.9 ppb. Since APIMS detects NO(2) direcdy within its system, the concentration of NO does not need to be measured. This system may be of great help in the accurate detection and determination of the concentration of low levels of NO(2) during inhaled NO therapy.

Inhaled nitric oxide: technical aspects of administration and monitoring

OBJECTIVES

Clinical applications of inhaled nitric oxide (NO) therapy resulted in the development of delivery systems and monitoring devices applicable to routine clinical care. This article presents the various components necessary for an adequate clinical use of inhaled NO, and discusses the NO gas mixture cylinders, inhaled NO delivery techniques and specifications, monitoring devices, and ending with an exhaustive description of the scavengers of nitrogen oxides (NOx).

DATA SOURCES

Computerized search (CURRENT CONTENTS, MEDLINE) of published original research and review articles (approximately 200), conference abstracts and compendiums up to May 1997 (approximately 50), personal files, and contact with expert informants.

STUDY SELECTION

Technical, experimental, and clinical reports were selected from the recent English, French, German, and Spanish literature, if pertinent to the administration or monitoring of inhaled NO.

DATA EXTRACTION

The authors extracted all applicable data.

DATA SYNTHESIS

The production of NO gas mixture cylinders must be certified with respect to gas purity, stability, and concentration (limits between 100 and 1000 ppm), guaranteed calibration, and specific color. An ideal inhaled NO delivery device requires a synchronized delivery, a minimal production of nitrogen dioxide (NO2), and should be simple to use (verification, calibration, convenient flushing, cylinder change possible while in use and a simple alarm setting) with full information (high and low alarms and available precision monitoring of NO, NO2, and O2). Emergency and transport systems must be readily available. The choice of the monitoring device (chemiluminescence or electrochemistry) should be made based on the knowledge of their strength and weakness for a particular clinical application. Finally, scavengers of NOx should be used with caution until specific filters are proven safe and effective.

CONCLUSIONS

The great expectancies generated by inhaled NO action have led researchers to design personal inhaled NO delivery systems, but only with mitigated results. At present, medical companies are finding a financial interest in designing a delivery system which will suit the needs of clinicians and this, along with official governmental approval, will only then permit the use of inhaled NO safely and on a larger scale.

An evaluation of a new analyser for inhaled nitric oxide administration

We examined the ability of a new combined nitric oxide (NO)/nitrogen dioxide (NO2) electrochemical analyser (PrinterNOx, Micro Medical Limited, Chatham, Kent, England) to measure NO and NO2 concentrations. The PrinterNOx was compared to a chemiluminescence analyser (42H, Thermo Environmental Instruments Inc, Franklin MA, U.S.A.). NO and NO2 were generated in a standard ventilator circuit using a paediatric ventilator (900C, Siemens Elema, Sweden) connected to an artificial lung (260li, TTL Test Lung, Michigan Instruments, MI, U.S.A.). Forty-four paired NO measurements ranging from 2.56 ppm to 74.6 ppm and 50 paired NO2 measurements ranging from 0.0 ppm to 5.39 ppm were obtained. For the measurement of NO the PrinterNOx showed a tendency to overestimate the chemiluminescence analyser. Regression analysis showed a close relationship between the two analysers with r2 = 0.9981 and a regression equation of y = 1.1658 x +0.0197. In the more clinically important range of 0-25 ppm, r2 increased to 0.9996 with a regression equation of y = 1.1984 x -0.4657. Conversely the PrinterNOx underestimated the chemiluminescence analyser for the measurement of NO2. The regression equation describing this relationship was y = 0.879 x -0.0447 (r2 = 0.9993). We conclude that the PrinterNOx is of sufficient accuracy to be of clinical use in the administration of NO.

Nitric oxide: delivery, measurement, and clinical application

The biologic and therapeutic roles of NO are rapidly being elucidated. Before inhalational NO administration is commonplace, there is a clear need for consensus regarding safe and accurate delivery and measurement systems. The potential for NO usage appears large and potentially life-saving; yet multicenter trials need to carefully evaluate efficacy and safety.

Clinical applications of inhaled nitric oxide in children with pulmonary hypertension

We have presented our experience with the use of inhaled nitric oxide in children with congenital heart disease and pulmonary hypertension, which indicates that nitric oxide is a selective pulmonary vasodilator that may improve patient management, particularly after surgical procedures requiring cardiopulmonary bypass. Indeed, we have now seen several patients in whom all resuscitative maneuvers for the treatment of pulmonary hypertensive crises were unsuccessful until inhaled nitric oxide was added to the therapeutic regimen. In addition, our studies using inhaled nitric oxide as an investigational probe point toward endothelial injury as a contributor to post-cardiopulmonary bypass pulmonary vasoconstriction. Inhaled nitric oxide relieves pulmonary vasoconstriction associated both with left atrial or pulmonary venous hypertension and following the relief of mitral valve or pulmonary venous obstruction. Absence of a response on the usually reactive pulmonary vascular bed of the neonate should prompt a careful search for anatomic, and possibly surgically remediable, pulmonary vascular obstruction. In the short term nitric oxide is less effective in the older patient with obliterative pulmonary vascular disease. It is possible that recent experimental work with long-term nitric oxide inhalation might be applicable to this group of patients. Nitric oxide may have a unique role in the management of the patient after lung transplantation, as it both reduces right ventricular afterload and improves intrapulmonary shunting. Is nitric oxide the ideal agent for testing pulmonary vascular reactivity? Nitric oxide is simple to deliver by either mask or ventilator and, as a trial of vasoreactivity over 15 min, remains free of side effects that might be encountered during long-term administration, such as methemoglobinemia or nitrogen dioxide toxicity. Indeed, no patient developed significant methemoglobinemia after a trial of nitric oxide and neither was a level of nitrogen dioxide above 1 ppm registered during the administration. Thus, nitric oxide gas fulfills many of the ideal characteristics, as suggested by Rubin,92 required of a drug to test the acute responsiveness of the pulmonary circulation. It has better pulmonary dilating effects than systemic, a short half-life, and minimal adverse effects and it can be both easily and quickly administered. Whether it is able to reliably predict the effect of long-term administration of orally active agents awaits confirmation. Certainly, inhaled nitric oxide is rapidly becoming the standard agent to test pulmonary vascular reactivity during diagnostic cardiac catheterization at our institution.