MINIMIZING NITROGEN DIOXIDE EXPOSURE DURING INHALED NITRIC OXIDE THERAPY.2105

Inhaled nitric oxide (INO) is an investigational therapy for pulmonary hypertension in adults and children. One of the main toxicities associated with its use is lung injury from nitrogen dioxide (NO₂) exposure. Efforts to limit the toxicity should focus on minimizing patients' NO₂ exposure. NO₂ is formed when mixing NO and oxygen at a rate dependent on the concentration of oxygen and the square of the concentration of NO. Equation

During clinical use, the period during which NO and oxygen are mixed prior to inhalation should be strictly limited. Careful handling of NO source cylinders is critical. One mililiter of room air introduced into a 4000 liter 800 ppm cylinder can theoretically increase the NO₂ concentration by 105 ppb.

METHODS: Procedures were developed through the collaboration of clinicians, a biomedical engineer and a NIST gas metrology scientist with the goal of minimizing NO₂ exposure during INO therapy.

RESULTS: The following procedures were developed:

• 1 Standard equipment set-up with introduction of NO into ventilator circuit shortly before patient inhalation.

• 2 Use of NO alarm with automatic gas shut-off.

• 3 Calibration of NO/NO₂ analyzer with NIST traceable reference material (NTRM).

• 4 Maintenance of a calibration log to follow the performance of the NO/NO₂ analyzer.

• 5 Measurement of NO₂ in NO source tanks in a nitrogen matrix to screen for NO₂ contamination.

• 6 Return of NO source cylinders which would provide greater than 1 ppm NO₂ delivery to the patient.

• 7 Vacuum purging of NO source and calibration cylinders to avoid NO₂ contamination.

CONCLUSION: Adherence to these procedures will minimize NO₂ exposure during INO therapy.