The Science Journal of the American Association for Respiratory Care

1997 OPEN FORUM Abstracts

SIDESTREAM SAMPLING OF NITRIC OXIDE CAN IMPAIR MECHANICAL VENTILATION

Jenni L. Raake, BS, RRT and James Johnson, CRTT Children's Hospital Medical Center, Cincinnati, Ohio

Background: A vital part of delivering Nitric Oxide involves sampling of gases for analyzation of NO and NO_{2} levels. Analyzing NO and NO_{2} is performed by using either sidestream or mainstream sampling techniques. Some sidestream analyzers require active gas flow to determine NO and NO_{2} levels. We set out to determine if sidestream sampling involving active gas flow can impair mechanical ventilation. Methods: We tested a Siemens Servo 900C (Danvers, MA) with a Biotek VT-1 ventilator tester (Winooski, VT). The ventilator was set at an SIMV rate of 20, an inspiratory time of 1 second, and tidal volumes of 200, 300, and 400cc using a 15 mm circuit (Allegiance Healthcare Corp., Round Lake, Il). Nitric Oxide was blended with Nitrogen using a stainless steel blender (Bird Corp., Palm Springs, CA). The ventilator air hose was connected to the blender and oxygen hose was connected to clinical oxygen. An Ecophysics CLD 700 AL chemiluminescence analyzer (Ann Arbor, MI) was used to monitor NO and NO_{2} levels at the inspiratory line of the ventilator circuit. Set tidal volumes were compared to tidal volumes measured by the test lung during sampling (active gas flow) and when the analyzer was not being used. The tests were repeated three times to insure reliability of results. The CLD 700 AL sampling flow rate was measured using a Fischer and Porter (Warminster, PA) flowmeter. Results: When tidal volumes were set at 200 cc, the test lung measured a tidal volume of 190 cc without sampling, and 140 cc during sampling. When tidal volumes were set at 300 cc, the test lung measured a volume of 295 cc without sampling, and a volume of 250 cc during sampling. When tidal volumes were set at 400 cc, the test lung measured a tidal volume of 395cc without sampling, and a tidal volume of 325 cc during sampling. Experience: When NO and NO_{2} levels are analyzed, sampling at the inspiratory limb of the ventilator circuit occurs before the set tidal volume is delivered to the patient. During active gas flow, sampling removes volume from the ventilator circuit before delivery to the patient. The amount of volume removed depends upon the sampling flow rate of the analyzer. The CLD 700 AL generates a sampling flow rate of 0.33 lpm. Other analyzers may generate more or less vacuum. Conclusions: Based on the results of the above tests, active sampling can impair mechanical ventilation due to removal of volume from the ventilator circuit. As a result, volumes should be adjusted during NO and NO_{2} sampling to assure appropriate mechanical ventilation of the patient.

(See original for figure)

OF-97-025

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