Inhaled nitric oxide monitoring
Carlos A. Fajardo
Jim Prokopowich
Jaques Belik
Department of Pediatrics, University of Manitoba and Manitoba
Department of Environment and Workplace Safety and Health,
Winnipeg, Manitoba
(Original manuscript submitted 12/4/94; received in revised form
4/10/94; accepted 5/10/94)
Abstract
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
FiO2 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 continuons 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.
Clin Invest Med 1995; 18 (2): 114-121
Table of contents: CIM vol. 18, no. 2
Copyright 1996 Canadian Medical Association