1995 OPEN FORUM Abstracts
NITRIC OXIDE (NO) AND NITROGEN DIOXIDE (NO_2) LEVELS DURING MANUAL VENTILATION.
Ray Ritz BA, RRT, Dean Hess PhD, RRT, C Alvin Head MD, Robert Kacmarek PhD, RRT. Respiratory Care and Anesthesia, Massachusetts General Hospital and Harvard Medical School, Boston, MA.
Mechanically ventilated patients who are administered inhaled NO to support oxygenation or reduce pulmonary artery pressure may require surgical or diagnostic procedures not available at the bedside: This requires manual ventilation during transport. Tolerance of the discontinuation of NO and manual ventilation with an FIO_2 of 1.0 varies between patients. We evaluated the clinical feasibility of maintaining NO and NO_2 levels with laboratory conditions of simulated manual ventilation.
Methods: A disposable adult manual resuscitator (Intertec, Fort Myers, FL) was attached to a mechanical lung model and a respirometer. A gas sample port and an O_2 analyzer were placed in sequence between the resuscitator and the lung. A pneumatically powered valve directed all gas delivered from the lung into the room, thus avoiding inadvertent measurement of NO_2 formed in the lung. A Y-connection was inserted into the resuscitator's O_2 supply tube 18 in from the bag and NO (809 ppm) was added from a 0 - I L flow meter until the desired source NO level was obtained (condition A - 10 ppm, condition B - 20 ppm, and condition C - 40 ppm). The source NO/NO_2 level was confirmed using a chemiluminescence NO/NO_2 analyzer (Eco Physics Model CDL 700AL). Source gas flow was varied at 10 and 15 L/min. Tidal volumes of 0.5 and 1.0 L were delivered at rates of 10 and 20/min. NO_2 was also measured in the resuscitator after 5 min of non-use following the 10/min - 0.5 L run. Each condition was repeated 3 times and the mean reported.
Results: Data obtained from source gas flow of 15 L/min appears in the table below. Data with source gas set at 10 L/min differed only in that the delivered NO varied more from the source NO as the minute ventilation increased. The delivered FIO_2 maintained a similar relationship with the source FIO_2 as did the NO in both source flow conditions. Ambient NO and NO_2 levels prior to testing were measured at 0.025 and 0.022 ppm, respectively. Immediately after the highest flow (15 L/min) of 39.5 ppm NO, ambient NO and NO_2 levels were 0.057 and 0.057 ppm, respectively.
NO Source V_T 0.5 L V_T 0.5 L V_T 1.0 L V_T 1.0 L 5 min
Condition NO Levelrate 10/min rate 20/min rate 10/min rate 20/min non-use
A 10.7 ppm10.3 9.9 9.9 6.5
B 20.0 ppm18.9 17.9 18.3 14.6
C 39.5 ppm38.1 37.2 37.2 29.8
A 0.1 ppm 0.3 0.1 0.2 0.1 0.6
B 0.4 ppm 0.5 0.2 0.1 0.1 1.2
C 1.6 ppm 2.1 1.7 1.8 0.6 3.5
CONCLUSION: Delivered NO concentrations can vary from the source NO as minute ventilation increases. Higher source gas flows may help maintain the desired inspired NO level. When delivering 20 ppm NO or less, NO_2 concentrations may fall within an acceptable range, but periods of non-use can result in temporary but significant increases of NO_2 in the resuscitator. Scavenging NO and NO2 during transport is difficult and may not be necessary.