The Science Journal of the American Association for Respiratory Care

1996 OPEN FORUM Abstracts

EFFECT OF HIGH FREQUENCY OSCILLATORY VENTILATION ON ELECTROCHEMICAL NITRIC OXIDE AND NITROGEN DIOXIDE SENSORS

Pitre Maurice RRT, Hill Wrae B.Sc RRT, Miller Chris, BA RRT BC Children's Hospital. Vancouver: KFSH & RC, Riyadh, Respiratory Care Department. UBC. Experimental Medicine

Introduction: Inhaled nitric oxide therapy (INO) may improve pulmonary hyperension and ventilation-perfusion mismatching in the critically ill. Safety guidelines for safe administration of INO delivery have evolved over the last few years. One of these safety precautions is the need for continuous monitoring of nitric oxide (NO) dosage and production of nitrogen dioxide (NO_{2}) Electrochemical measurement technique of NO and NO_{2} in conjuction with continuous-flow-time cycled infant ventilators has been established as a effective methodology during INO administration It has been suggested that INO may be a useful adjunct therapy along with high fquency oscillatory ventilation (HFOV). It is unknown how electrochemical NO and NO_{2} sensors will react in this new environment. The purpose of this study was to bench test the effectsof HFOV on these sensors and report any observations that may be useful to researches utilizing these two modes of therapy together. Methods: A HFOV ventilator (3100A, SensorMedics. USA) was use with the following therapeutic settings Bias flow=20 Lpm, Mean airway pressure maintained between 15 - 30 cmH_{2}O. Frequency = 2.8 - 15 Hz; Inspiratory time = 33%, and change in pressure (\deltaP) 20 - 80 cmH_{2}O. Nitric oxide was delivered from a source tank (Liquid Air, Canada) of 2000 parts per million (ppm) with a standard flow-rotometer and a double-stage stainless steel regulator. Nitric oxide was bled into the ventilator circuit just prior to the humidifier. NO and NO_{2} was continuously monitored utilizing two electrochemical momtors (Pulmonox II, Pulmonox Medical Crporation. Canada). Samples were drawn from the inspiratory limb of the ventilator circuit just prior to the patient-wye. Both analyzers were calibrated as per manufacturer's instructions using side-stream sample technique at a rate of 150 cc min^{-1}. Base line measurements of NO and NO_{2} were made without oscillations at a mean airway pressure of 20 cmH_{2}O, bias flow of 20 Lpm and 20 ppm NO dosage. Measurements of NO and NO_{2} were recorded while independent alterations in mean airway pressure and frequency were made (2.8, 5, 7.5, 10, 12.5, and 15 Hz and \deltaP of 20, 40, 60 and 80 cmH_{2}O). The suggested side-stream sampling circuit was then altered by either deleting and/or exchanging the following items: 1) small hygroscopic filter, 2)large bacterial filter, 3) standard high-pressure arterial sampling line and 4) oxygen tubing. Results: There was no significant difference between the two analyzers(p>0.05) Altering mean airway pressure and frequency had no significant effect on NO and NO_{2} readings (p>0.05). Change in \deltaP had no significant effect on NO_{2} measurements but a highly significant (p < 0.0001) directly proportional effect on NO readings at all levels >20 cmH_{2}O and Changes were as great as 100 ppm at a \delta P of 80 cmH_{2}O. This could be significantly ameliorated (p>0.05) by changing the manufacturer's suggested sampling system as follows: 1) Adding a small hygroscopic filter and 2)replacing the oxygen tubing sampling line with a smaller bore high-pressure arterial sampling line. Conclusion: This study suggests that oscillatory changes of the \delta P parameter in HFOV has a highly significant effect on the NO reading of this electrochemical analyzer. We hypothesize that the same high frequency amplitudes which enhance alveolar diffusion may indeed increase molecular activity in the electrochemical NO sensor resulting in abnormally high NO readings. However,this observed effect can be fully ameliorated by altering the sampling line to function as a low pass filter-like system which eliminates high frequencies with large amplitudes but allowing low sampling flows This study also underscores the importance of bench testing systems when different modes of therapy and equipment are combined to ensure that one does not adversely affect the other.

Reference: OF-96-074

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