[Inhaled nitric monoxide. Application and continuous measurement of concentration]

Inhaled nitric oxide (NO) is a selective pulmonary vasodilator that may be useful in the treatment of patients with severe pulmonary hypertension. We describe a delivery system of inhaled NO that allows safe application and continuous measurement of the inspired NO concentration during mechanical ventilation. From a gas cylinder containing NO in N2 (600 ppm NO), an adjustable amount of gas is introduced into the inspiratory side of the tubing system via a pressure reduction valve, a magnetic valve, and a special injection nozzle. The NO concentration is diluted to the desired value by the tidal volume. The magnetic valve is connected to the ventilator and opens at the beginning of each inspiration and closes after a predetermined time. The gas volume is proportional to the pressure at the magnetic valve and the opening time. To monitor the inspiratory NO concentration, a specimen of gas is taken from an angle-connector and passed over an electrochemical sensor. The second nozzle of the sensor is connected to a water seal, which is adjusted to the positive end-expiratory pressure level of the ventilator to insure that the gas flow over the sensor is limited to inspiration.