PRECISE CONTROL OF NITRIC-OXIDE CONCENTRATION IN THE INSPIRED GAS OF CONTINUOUS-FLOW RESPIRATORY DEVICES

Inhaled NO has become widely used for diagnosis and therapy of pulmona ry hypertension. The potential hazards of NO inhalation include the fo rmation of methemoglobin, formation of NO2, and generation of free rad icals in the presence of humidity and oxygen. Careful monitoring of NO and NO2 concentration, and titration of the dose according to a patie nt's clinical response is essential to minimize toxicity. This paper d escribes a formula and method that permits calculation and precise con trol of NO concentration in the inspired gas. The accuracy of the deli very system was assessed by a comparison of calculated and measured NO and NO2 concentrations in a continuous flow ventilator circuit. A com parison of electrochemical detector (ECD) versus chemiluminescence det ector (CLD) monitoring techniques showed agreement between the instrum ents within similar to 2 ppm, with the ECD averaging a higher reading than the calculated or CLD measured values. We deemed a 2 ppm discrepa ncy between instruments clinically acceptable, and concluded that the instruments could be used interchangeably for clinical purposes to mea sure NO, and that the ECD was preferable to CLD for measuring NO2, Det ails about the equipment are given and techniques are discussed to avo id the risk of inhalation of toxic concentrations of NO and NO2. This method provides the possibility of using inhaled NO with appropriate s afety precautions in the range 0-60 ppm in a variety of continuous flo w respiratory devices. (C) 1996 Wiley-Liss, Inc.