Nitric oxide (NO) is a gas that, when inhaled, acts to dilate blood vessels in the lungs, improving oxygenation of the blood and reducing pulmonary hypertension. Because of this, nitric oxide is provided as a therapeutic gas in the inspiratory breathing gases for patients with pulmonary hypertension.
Typically, inhaled NO is delivered in a carrier gas from a high pressure source (such as a pressurized cylinder) to the patient at or near ambient pressure by means of a respiratory tube for ICU ventilator bound or anesthesia patients or a nasal cannula for spontaneously breathing patients. It is particularly challenging to deliver an accurate and consistent dose to the patient through a nasal cannula as dilution of the dose can occur through retrograde flow and diffusion of other gases.
Delivery of NO may require transit through a nasal cannula. During patient inhalation and exhalation, a driving pressure gradient can cause retrograde flow in the nasal cannula supply lumen, thereby diluting the NO dose in the cannula with exhaled gas. In addition, diffusion of ambient gasses can occur through the cannula itself during the transit time of NO through the cannula. Oxygen is of specific concern as it reacts with NO to form nitrogen dioxide (NO2) thereby reducing the NO concentration. This is further exacerbated by the fact that patients on NO may also require oxygen therapy. Both of these issues can dilute the delivered dose of NO during inhaled NO therapy.
Accordingly, there is a need for new methods and apparatuses for preventing dilution of dosing within the delivery conduit of a nitric oxide delivery apparatus.