Nitric oxide (NO) measurement accuracy.

Background: Evaluation of the clinical utility of NO requires accurate assessment of inspired [NO]. Currently, chemiluminescence analyzers are the clinical standard for analysis; however, their performance in the clinical setting has not been systemically evaluated.

Methods: We evaluated the performance of four chemiluminescence analyzers (270B NOA, Sievers Instruments, Inc.; CLA 510S, Horiba Co., Ltd.; CLD 700 AL, Eco Physics Corp.; Model 42, Thermo Environmental Instruments Inc.) in simulated clinical settings. Transport delay and dynamic 95% response time were measured by the balloon in a glass chamber puncture technique. Fluctuating [NO] in a continuous flow of gas and [NO] during mechanical ventilation, where NO was premixed prior to entering the ventilator, were evaluated.

Results: Transport delay ranged from 1.02 +/- 0.02 to 24.36 +/- 2.47 s (p < 0.05) and the 95% response time ranged from 0.22 +/- 0.04 to 70.03 +/- 0.03 s (p < 0.05). Accurate analysis of [NO] in a continuous flow system was only possible with the most rapid response analyzer (270B NOA). All other analyzers under reported the maximum [NO] (p < 0.05) and over reported the minimum [NO] (p < 0.05). All analyzers accurately determined [NO] in the inspiratory limb of the ventilator circuit, but none accurately determined [NO] at the airway opening.

Conclusions: Measurements of inhaled [NO] can vary greatly, dependent upon the performance characteristics of the analyzer and the location of NO analysis. All studies evaluating the clinical use of NO should fully describe the technical gas delivery methodology and the response time and transport delay of the chemiluminescence analyzer used.