Correspondence  |   December 1997
Inhaled Nitric Oxide Delivery Systems 
Author Notes
  • Ph.D. Student (Troncy); Anesthesiologist, Associate Professor, and Director (Francoeur, Blaise); Anesthesia Laboratory, Department of Anesthesiology, Centre Hospitalier de l'Universite de Montreal, Pavillon Notre-Dame, 1560 Sherbrooke Street East, Montreal H2L 4M1, Canada.
Article Information
Correspondence   |   December 1997
Inhaled Nitric Oxide Delivery Systems 
Anesthesiology 12 1997, Vol.87, 1591-1592. doi:
Anesthesiology 12 1997, Vol.87, 1591-1592. doi:
To the Editor:-Imanaka et al. [1 ] informed us about the inaccuracies of nitric oxide (NO) delivery systems during adult mechanical ventilation. Although we found the study informative, we have some concerns regarding the methodology and the manner in which the authors interpret their results.
Although the authors argue for the analysis of only “a single breath …,” we have major concerns with such results. In the cited conditions, no statistical analysis is possible, hence no inference can be made. Moreover, explanations of the changes Table 2 in fractions of inspired NO (NO concentration) observed by varying tidal volume (VT) or inspiratory time (T1) would have been appreciated. The authors claim that during pressure support ventilation into inspiratory phase, injection into inspiratory limb (fig. 5, panel ii) is not acceptable. However no obvious difference is observed between this and NO concentration-premixing systems with synchronized intermittent mandatory ventilation, and it is unclear how the authors explain the sudden appearance of a high peak of NO concentration in the ii mode with a mandatory breath?
Continuous and premixed administrations of NO were used at the very early stages of inhaled NO therapy. Continuous injection is simple, but it results in high peak NO concentration, [2,3 ] often not recorded by slow-response analysers, [4 ] high production of nitrogen dioxide (NO sub 2), and reduction in FIO2. It is characterized by a bolus effect [5 ] and would require an appropriate mixing chamber or continuous bypass flow to avoid it. This method is currently not recommended, except with continuous-flow time-cycled pressure-limited or high-frequency mechanical ventilators.
Premixing NO with nitrogen (N2) or air (supplemental diluting cylinder) also presents major drawbacks. Blenders, valves, and other ventilator components were not specifically designed to withstand NO. Even if this method has been used over a period of 20 months without apparent corrosive effects, [6 ] long-term safety has not been verified. [7 ] Most blenders also have a bleed flow delivered in the room, and the NO concentration changes when the FIO2setting on the ventilator is changed. The validity of the used nomograms to adjust NO dilution is suspect, [4 ] and we observed difficulty achieving a precise NO concentration. At high FIO2, high levels of NO2can be produced. [8 ]
Using their cyclic NO delivery system, the authors have shown a high variability in NO concentrations. This was particularly evident in the pressure-controlled (PCV) mode where peak inspiratory flow rate is high and decelerating. This may be a problem of the efficacy of their system, and the authors should be prudent before ruling out cyclic NO injection in the inspiratory limb. It appears that this method also is the choice of many companies developing NO delivery systems (Servo 300[trademark symbol] with NO option, Drager Nodomo[trademark symbol], Messer-Griesheim Pulmonox[trademark symbol], L'Air Liquide Opti-NO[trademark symbol], Ohmeda I-NOvent[trademark symbol]). No study has evaluated whether physiologically significant effects occur if NO concentration fluctuates around a mean therapeutic value during inspiration. We think that the latter method can be used to deliver inhaled NO safely and efficiently and that such systems must meet the needs of different ventilatory modes and peak inspiratory flow rates.
Eric Troncy, D.V.M., M.Sc.
Ph.D. Student
Martin Francoeur, R.R.T.
Gilbert Blaise, M.D.
Anesthesiologist, Associate Professor, and Director; Anesthesia Laboratory; Department of Anesthesiology; Centre Hospitalier de l'Universite de Montreal; Pavillon Notre-Dame; 1560 Sherbrooke Street East; Montreal H2L 4M1; Canada
(Accepted for publication August 6, 1997.)
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