Abstract
BackgroundInhaled nitric oxide (NO) is a selective pulmonary vasodilator used primarily in the critical care setting for patients concurrently supported by invasive or noninvasive positive pressure ventilation. NO delivery devices interface with ventilator breathing circuits to inject NO in proportion with the flow of air/oxygen through the circuit, in order to maintain a constant, target concentration of inhaled NO.MethodsIn the present article, a NO injection and mixing element is presented. The device borrows from the design of static elements to promote rapid mixing of injected NO-containing gas with breathing circuit gases. Bench experiments are reported to demonstrate the improved mixing afforded by the injection and mixing element, as compared with conventional breathing circuit adapters, for NO injection into breathing circuits. Computational fluid dynamics simulations are also presented to illustrate mixing patterns and nitrogen dioxide production within the element.ResultsOver the range of air flow rates and target NO concentrations investigated, mixing length, defined as the downstream distance required for NO concentration to reach within ±5 % of the target concentration, was as high as 47 cm for the conventional breathing circuit adapters, but did not exceed 7.8 cm for the injection and mixing element.ConclusionThe injection and mixing element has potential to improve ease of use, compatibility and safety of inhaled NO administration with mechanical ventilators and gas delivery devices.
Highlights
Inhaled nitric oxide (NO) is a selective pulmonary vasodilator used primarily in the critical care setting for patients concurrently supported by invasive or noninvasive positive pressure ventilation
For the 2 and 40 l/min air flow rates, both versions of the injection and mixing element yielded NO concentration within ±5 % of the final target concentration at all sampling locations for all three target concentrations
Computational fluid dynamics simulations CFD simulations of NO concentration downstream from injection points were qualitatively similar to the experimental measurements, and permit visualization of the mixing process inside the adapters and the injection and mixing element
Summary
Inhaled nitric oxide (NO) is a selective pulmonary vasodilator used primarily in the critical care setting for patients concurrently supported by invasive or noninvasive positive pressure ventilation. NO delivery devices interface with ventilator breathing circuits to inject NO in proportion with the flow of air/oxygen through the circuit, in order to maintain a constant, target concentration of inhaled NO. The vast majority of patients receiving inhaled NO do so in the critical care setting, and are concurrently supported by invasive or noninvasive positive pressure ventilation. The injection flow rate is adjusted in proportion to the flow rate of air/oxygen in the circuit so as to maintain a constant, target NO concentration in the inhaled gas mixture. Dosing recommendations have been established based on the NO concentration in inhaled gas [4, 8]
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