The Science Journal of the American Association for Respiratory Care

1997 OPEN FORUM Abstracts


William Howard, MBA, RRT. Respiratory Care, New England Medical Center, Boston, MA.

BACKGROUND: Therapies such as hyperoxygenation, hyperventilation, and intravenous vasodilators have provided limited success in reversing persistent pulmonary hypertension of the newborn, and hypoxemic respiratory failure. Nitric oxide (NO) is an investigational new drug for the treatment of these disorders. On occasion, patients fail NO treatment and must be referred to an ECMO center. However, dependency on NO necessitates continuation of treatment during transport. Otherwise, the patient clinically deteriorates. The most common method of supplying NO during transport has been with a manual resuscitation device which is supplied with a blend of oxygen and NO delivered from separate flowmeters. Because such a low flow of nitric oxide is required, and because they are difficult to regulate, we had concerns about our ability to provide a stable NO flow during transport using a flowmeter. We evaluated the delivered accuracy of low flow bourdon gauges. Evaluated were a Flotec model RRN0S4SSC4, Flotec Inc., Indianapolis, IN, Western Medica model XA-2801, Westlake, OH, Victor model LSS-64, Victor Medical, Denton, TX low flow bourdon gauges, compared to calculated values and Timeter model Classic 200 or 1000 low-flow flowmeters, Allied Healthcare Products, Inc., St. Louis, MO. Methods: A test circuit was assembled which consisted of a Y-connection having a common feed into 28 inches of aerosol tubing. Oxygen, at 10 LPM, supplied 1 side of the Y-connection. NO in the concentration of 800 ppm, (balance nitrogen) was delivered by the bourdon gauge to the other port of the Y-connection. The common outlet of the Y-connection was connected to the test circuit using 18 inches of O2 supply tubing. Bench testing was performed on 4 bourdon gauges at the following settings; (Flotec at 0, 20, 25, 50, 100, 250, 500, 750, and 1,000 ml; Victor Medical at 0, 100, 500, and 1,000 ml; Western Medical at 0, 250, 500, 750 and 1,000 ml). The gauges were set to comparative settings common to the other gauges tested. We then tested delivered NO using the Timeter flowmeters, at 0, 20, 25, 50, 100, 250, 500, 750, and 1,000ml. Testing consisted of three 10 minute runs at each setting with 0, 5 and 10 cmH20 of PEEP. During each of the trials the delivered NO concentration was continuously sampled using a side stream analysis method. Analysis was performed using an electrochemical device, (Pulmonox II, Pulmonox Medical Corporation. Canada). The measurements were recorded at 10 minute intervals. The analyzer was calibrated per manufacturer's instructions. Results were compared to the calculated value for the settings tested. This calculation is represented by the following equation [NO dose = NO source ppm (NO flow rate/total flow rate)]. Results: Calculated and mean measurements, with SD, of NO delivered and correlation between measured NO and calculated NO are in the following table:

Flowrate (ML/MIN)

BRAND 0 20 25 50 100 250 500 750 1000

CALCULATED 0.0 1.0 2.0 4.0 7.9 19.5 38.0 56.0 73.0

Timeter 0.0 0.0 1.7 2.0(0) 7.3 19.3 36.7 56(2) 73.3

Classic (0.6) (1.2) (1.2) (1.2) (3.1)

FLOTEC 0.0 0.0 0.0 0.3 5.3(4) 20(4) 39.3 54.3 73

(.6) (3.5) (5.5) (7.8)

WESTERN 0.0 26(1) 45(4) 64.3 84

(5.7) (7.5)

VICTOR 0.0 8.7(1.2) 36.3(2.3) 73.3(7.6)

Correlation: Timeter 1.0 Flotec 1.0 Western 1.0 Victor 1.0

CONCLUSION: Bourdon gauges deliver reasonably accurate flows, of NO at settings >= 100 cc/min. There is a high correlation of NO delivery when compared to calculated predicted values. Bourdon gauges can be a reasonable alternative to flowmeters for providing safe NO delivery while transporting patients with or without PEEP. They are less susceptible to accidental mis-dosing when compared to flowmeters.