Fluctuations of inspired concentrations of nitric oxide and nitrogen dioxide during mechanical ventilation

Background:
Nitric oxide (NO) is a very reactive agent with potentially toxic
oxidation products such as nitrogen dioxide (NO2). Therefore, during
NO inhalation a constant inspired concentration and accurate measurement of NO
and NO2 concentrations are essential. The objective of this study
was to test the NO concentrations at various positions along the inspiratory
limb of the breathing circuit using a recently developed system to administer
NO in phase with inspiratory flow during mechanical ventilation (Servo 300
NO-A, Siemens, Sweden). Furthermore, we tested whether an active heating system
would interfere with inspired NO concentrations.

      Results:
      A sharp decline in the NO concentration was found between the
            respirator's inspiratory outlet and more distal points along the inspiratory
            limb of the circuit. This finding was most evident when an active heating
            system was mounted between those points.


      Conclusions:
      The concentrations of NO and NO2 should be measured as
            near to the patient as possible, as significant fluctuations of these
            concentrations might be found along the inspiratory limb of the respiratory
            circuit especially when an active heating system is used.