Flow-proportional administration of nitric oxide with a new delivery system: inspiratory nitric oxide concentration fluctuation during different flow conditions

Nitrogen dioxide reducing ascorbic acid technologies in the ventilator circuit leads to uniform NO concentration during inspiration

Conventional inhaled NO systems deliver NO by synchronized injection or continuous NO flow in the ventilator circuitry. Such methods can lead to variable concentrations during inspiration that may differ from desired dosing. NO concentrations in these systems are generally monitored through electrochemical methods that are too slow to capture this nuance and potential dosing error. A novel technology that reduces NO2 into NO via low-resistance ascorbic-acid cartridges just prior to inhalation has recently been described. The gas volume of these cartridges may enhance gas mixing and reduce dosing inconsistency throughout inhalation. The impact of the ascorbic-acid cartridge technology on NO concentration during inspiration was characterized through rapid chemiluminescence detection during volume control ventilation, pressure control ventilation, synchronized intermittent mandatory ventilation and continuous positive airway pressure using an in vitro lung model configured to simulate the complete uptake of NO. Two ascorbic acid cartridges in series provided uniform and consistent dosing during inspiration during all modes of ventilation. The use of one cartridge showed variable inspiratory concentration of NO at the largest tidal volumes, whereas the use of no ascorbic acid cartridge led to highly inconsistent NO inspiratory waveforms. The use of ascorbic acid cartridges also decreased breath-to-breath variation in SIMV and CPAP ventilation. The ascorbic-acid cartridges, which are designed to convert NO2 (either as substrate or resulting from NO oxidation during injection) into NO, also provide the benefit of minimizing the variation of inhaled NO concentration during inspiration. It is expected that the implementation of this method will lead to more consistent and predictable dosing.

A fast, digitally controlled flow proportional gas injection system for studies in lung function

The aim of this paper is to describe a device for flow proportional injection of tracer gas in the lungs of mechanically ventilated patients. This device may then be used for the study of the multiple breath indicator gas washout technique to determine the end-expiratory lung volume. Such a tracer gas injection device may also be used in the study of other techniques that rely on uptake and elimination of tracer gas by the lungs. In this paper, an injector is described which enables injection of indicator gas at a predetermined concentration in a breathing circuit independent of the type of breathing. The presented setup uses a control computer to produce steering signals to a multivalve array in proportion to the input breathing signals. The multivalve array consists of ten circular valves, each with a different diameter, which can be opened or closed individually according to the input signal of the array. By opening of a certain combination of valves an amount of sulphur hexafluoride gas proportional to the inspiratory breathing signal is released. The rate of transmission between the components of the injection system was 80 Hz. The injector has a full flow range between 0-10 L/min. The delay time between the breathing signal and the flow response was 70 ms. The aimed washin gas concentration of 1% SF6 was achieved after 0.5 s. The study describes the results of tests to determine valve-flow ratios, step response and dynamic response of the injector. The flow output response of the injector system was shown to increase in input frequencies above 3 Hz. The valve flow ratios showed the largest relative deviation in the two smallest valves of the 10 valve array, respectively 0.005 L/min (25%) and 0.002 L/min (20%). We conclude that the injector can achieve a stable concentration of indicator gas in a breathing system with an accuracy of 0.005 L/min to execute the multiple breath indicator washout test in human subjects. The results of the study indicate that the injector may be of use in other application fields in respiratory physiology in which breathing circuit injection of indicator gas is required.

Nitric oxide and nitrogen dioxide concentrations during in vitro high-frequency oscillatory ventilation

PURPOSE

The purpose of this study was to measure nitric oxide (NO) and nitrogen dioxide (NO2) concentrations, at various ventilatory settings and sampling sites, during in vitro inhaled NO and high-frequency oscillatory ventilation therapy [iNO-HFOV].

MATERIALS AND METHODS

We used a high-frequency oscillatory ventilator (model 3100A, SensorMedics, Yorba Linda, CA), a test lung (model VT-2A Ventilator Tester, Bio-Tek Instruments, Inc., Winooski, VT), nitric oxide delivery and NO/NO2 monitoring (Pulmonox II, Pulmonox, Tofield, Canada), and scavenging systems in this study. The ventilator frequency, amplitude, and inspired oxygen concentration were systematically changed at a fixed flow of NO. The concentrations of NO and NO2, sampled at four sites, were determined by an electrochemical method (Pulmonox II). The NO and NO2 concentrations were measured at the proximal part of the inspiratory limb (site 1), near the Y-piece (site 2), the carina of the test lung (site 3), and the bellows of the test lung (site 4).

RESULTS

The concentration of NO decreased significantly (P < .001) from the proximal port (site 11 of the inspiratory circuit (86.16 +/- 0.38 ppm) through the lung bellows (site 4) (70.08 +/- 0.23 ppm). The concentration of NO2 increased significantly (P < .001) from site 1 (3.25 +/- 0.04 ppm) through site 4 (19.4 +/- 0.19 ppm). However, the total concentration of NO + NO2 (NOx) remained unchanged at both site 1 and site 4. Increasing the frequency and amplitude of the ventilator significantly altered NO and NO2 concentrations. The NO2 concentration increased significantly (P < .0001) from 5.6 ppm to 18.1 ppm at site 4 when the fraction of inspired oxygen was increased from 0.25 to 0.93. The NO2 concentration also increased significantly (P < .0001) from 0.6 ppm to 18.7 when NO concentrations were independently increased from 12 ppm to 80 ppm.

CONCLUSIONS

During HFOV, the concentrations of NO and NO2 vary between sampling sites and also are influenced by the frequency, amplitude, and inspired oxygen concentration. NO2 concentrations in the lung were significantly increased above commonly accepted toxic concentrations during ventilation with high concentrations of NO (80 ppm) and high fractional concentrations of oxygen. The excessive increase in NO2 concentration at the "alveolar" level in our test lung model warrants confirmation in an in vivo model.

Delivery of inhaled nitric oxide using the Ohmeda INOvent Delivery System

OBJECTIVES

We evaluated the Ohmeda INOvent Nitric Oxide Delivery System, which uses an inspiratory flow sensor to inject a synchronized and proportional nitric oxide (NO) flow into the mechanical ventilator circuit. This system should deliver a constant NO concentration independent of ventilator mode, minute ventilation, fraction of inspired oxygen, or ventilator brand. It should also minimize nitrogen dioxide (NO2) formation.

METHODS

NO delivery by the INOvent and a premixing NO delivery system were compared using two ventilators (Puritan-Bennett 7200 and Servo 900C). NO concentration was measured within the trachea of an attached lung model using a fast-response chemiluminescence NO analyzer. NO concentration was also measured in the inspiratory limb using the electrochemical analyzer of the INOvent. For three NO concentrations (2, 5, and 20 ppm), the ventilators were set for constant flow volume control ventilation, pressure control ventilation, and spontaneous breathing with pressure support ventilation or synchronized intermittent mandatory ventilation. Different tidal volumes (300, 500, 750, and 1,000 mL) and inspiratory times (1 and 2 s) were evaluated. NO2 formation for both ventilators and delivery systems were evaluated at 20 ppm and 95% O2-.

RESULTS

Regardless of ventilatory pattern, both systems delivered a constant NO concentration. The error between the target and the delivered NO dose for the INOvent was -1.3+/-3.6% with the Puritan-Bennett 7200 and -3.9+/-4.3% with the Servo 900C. For the premixing system, the error was -5.5+/-4.8% with the Puritan-Bennett 7200 and -6.7+/-6.2% with the Servo 900C. NO2 concentrations were 0.5+/-0.1 ppm during NO delivery by the INOvent, 5.8+/-1.6 ppm when NO was premixed with air, 0.3+/-0.1 ppm when NO was premixed with N2.

CONCLUSION

The INOvent provides a constant NO concentration independent of the ventilatory pattern, and NO2 formation is minimal.