[NO and NO2 concentration curves in mixtures for clinical use]

Inhaled nitric oxide (NO) allows us to achieve selective pulmonary vasodilatation. The purpose of the present experimental study was to determine the concentrations of NO and NO2 produced by mixing two well-known and variable flows of 100% oxygen and 800 ppm NO, in a low or normally humid environment, as well as in a humid one. The mixture of NO and N2 is introduced by means of a standard low-flow blender (0.2 to 1 liter/minute) in the inspiratory tube of a ventilator at a distance of about 20 cm from the connection with the artificial lung. In order to obtain a humid circuit, we used a humidifier servocontrolled at a temperature of 36 degrees C. The concentration of NO and NO2 are continually determined by means of chemiluminescence in the expiratory tube at about 5 cm from the connection with the artificial lung. The study consisted of three parts: elaboration of the curves of NO and NO2 in low humidity (34 measurements), validity of the corresponding curves of NO in low humidity (80 new measurements) and elaboration of the curves of NO and NO2 in a humid circuit (32 measurements). We found that the concentrations of NO in low humidity follow a lineal equation, except for the flows lower than 10 L/min. Flows between 10-15 L/min reached concentrations of NO between 6-60 ppm. The concentrations of NO2 in low humidity produced some parallel curves, and exceptionally overcame the toxic figure of 5 ppm. The curves are valid only with flows higher than 10 L/min. Humidity does not influence the NO concentrations, while it diminishes NO2 concentrations 1.4 times.