INHALED NITRIC-OXIDE MONITORING

Recently, inhaled nitric oxide (NO) became clinically available for the treatment of persistent pulmonary hypertension of the newborn. Such use requires administration and continuous monitoring of a very low concentration of NO to prevent potential toxicity. Since limited data on the reliability of NO monitoring devices are available, we evaluated the performance of a chemiluminescent and electrochemical sensor NO analyzer in a patient ventilator circuit. Results: The chemiluminescence analyzer readings were significantly altered by the oxygen concentration in the ventilator circuit. When the FiO(2) was increased from 0.21 to 1, a 4.5% +/- 0.3 decrease in the NO readings was found (p < 0.01). Similarly, adding humidity to the circuit, reduced the NO readings by 4.8% +/- 0.9 (p < 0.01). The effect of gas pressure was proportional to its magnitude but independent of whether a pulsatile or continuous gas flow was provided. At a mean airway pressure of 15 cm H2O, the NO readings increased by 3.94% +/- 0.05 (NO = 10 parts per million) and 3.97% +/- 0.02 (40 parts per million) (p < 0.01). The electrochemical sensor NO readings were directly proportional to the ventilator circuit pressure but independent of whether a pulsatile or continuous gas flow was provided. At a mean airway pressure of 15 cm H2O, the NO reading was increased by 25.39% +/- 0.04 (NO = 40 parts per million) (p < 0.01) and 1.07% +/- 0.16 (NO = 10 parts per million) (p NS). The greatest difference with NO = 10 parts per million from baseline was found at a mean airway pressure of 6 cm H2O (6.67% +/- 0.23; p < 0.01). In conclusion, the measurement of NO by the chemiluminescence technique was influenced by humidity, oxygen concentration and ventilator circuit gas pressure. Yet the observed changes were small and of questionable clinical significance, making this technique reliable to monitor patients receiving inhaled NO. In regards to the electrochemical sensor, the marked effect of gas pressure upon the NO reading precision makes this device less suitable for NO monitoring in a patient ventilator circuit.