The Science Journal of the American Association for Respiratory Care
Introduction: The use of inhaled nitric oxide (iNO) has been advocated for the treatment of pulmonary hypertension associated with ARDS and persistent pulmonary hypertension of the newborn. Delivery devices have been developed which allow the accurate monitoring and titration of nitric oxide (NO). Unfortunately, these system are large and bulky. This presents a problem for interfacility transport teams, as patients may need to be transported by aircraft while receiving the drug. We sought to compare the effects of altitude on a cohort of inhaled nitric oxide monitoring and delivery devices.
Methods: We compared the NoxBox I (Bedfont Scientific Ltd.), Pulmonox II (Pulmonox Inc.), INOvent (Datex / Ohmeda) and the AeroNox (Pulmonox Inc.) NO and nitrogen dioxide (NO2) monitors. Additionally, we compared the delivery systems of the INOvent and AeroNox devices. Device comparison was a two step procedure; evaluation of the analyzation of a know concentration of NO and NO2 gas, and evaluation of the delivery of a specific concentration of NO at altitude. Each device was calibrated at ground level (1400 feet above sea level) per manufacturers instructions. All testing was performed in a Bell 222 helicopter which maintained each altitude for approximately four minutes. Monitor Test: A continuous flow CPAP circuit (20 cmH20) was fed with five LPM of calibration gas (20 PPM NO and 7.3 PPM NO2). Sample lines from each device were connected to the circuit. Data collection consisted of direct observation of monitored NO and NO2 at five altitudes. Devices were allowed to stabilize at each altitude prior to data collection. Delivery Systems: Delivery devices were set up per manufacturers instructions to deliver 20 PPM into a 10 LPM continuous flow circuit. Each delivery device was connected to an 800 PPM source gas. Data collection consisted of measured NO and NO2 at five altitudes.
|* NO2 cell of the INOvent failed during the test.|
Discussion: Fuel cell technology routinely used in NO monitoring and delivery systems is susceptible to error at altitude. Manufactures contacted verify this as a potential limitation of this technology. The error observed with some monitoring and delivery systems may be clinically significant. Tolerable error for manufacturers may exceed acceptable clinical limits. Further investigation is warranted.
Conclusions: Altitudes attained during air transport may result in variable performance characteristics of NO monitoring and delivery systems.