1995 OPEN FORUM Abstracts
Environmental Exposure Of Nitric Oxide/ Nitrogen Dioxide In An Nicu During Simulated Mechanical Ventilation
Kelvin MacDonald, R.C.P.,C.R.T.T., John Cefaratt, B.S. R.R.T.. Kaiser Permannente, Los Angeles.
INTRODUCTION: Inhaled Nitric Oxide (NO) appears to be an effective tool in the treatment of Persistent Pulmonary Hypertension (PPHN) and as an alternative to ECMO. However, there are concerns about secondary exposure to health care workers. Some investigators, including ourselves use "scavenging" on the expiratory limb to reduce risk, others report they do not. We sought to measure the ambient levels of nitric oxide (NO) and nitrogen dioxide (NO2) in model of administration in an NICU.
Methods: In an vacant NICU (2500 sq. ft), we assembled an Infrasonic (San Diego, CA) Infant Star Classic ventilator, 80 cm long standard infant circuit with heater wires, Fisher & Paykel (New Zealand) MR 360 humidifier, and custom drop line to allow entrainment and sampling of NO/NO2. This was connected to a static test lung with compliance of 1 ml/cm H_2O, resistance 20 cm H_2O/L/sec. A Pulmonox II (Toefield, Canada) electrochemical NO/NO2 analyzer was setup and calibrated according to manufacturers specification. Measurements of NO and NO2 levels in the circuit were recorded at the drop line. Effluent gases were sampled through a special NO/NO2 sampling block connected to wall suction set at a rate sufficient to draw 12 l/m, measured by a Boehringer respirometer, 10 cm, from the exhalation port. Measurements were taken at 10 parts per million (PPM) step intervals from 10 PPM to 100 PPM introduced and measured at the patient circuit. Each step interval was recorded on both IMV (IMV 25, 25/3 .45 I. time, 1.0 FiO2) and HFV (MAP 10, .45 I. time, 1.0 FiO2, 30 amplitude and 10 Hz). 5 minutes were allowed for stabilization of each reading.
Results: Shown in the table.
Set NO PPM NO on IMV NO on HFV NO2 on IMV NO2 on HFV
100 0 00
200 0 00
30 0.5* 0 00
40 0.7* 0 00
501 0 00
601 0 00
70 1.5* 0 00
80 1.7*0.5* 00
100 2.5*1.5* 00
On IMV and HFV internally, read NO increased as set, from 10 PPM - 100 PPM. NO2 measurements increased from 0 PPM to 0.8 PPM at 100 PPM NO. On measurement at exhaust, NO increased from 0 PPM to 2.5 PPM during IMV (r=0.99), while NO2 was undetectable. On HFV, NO measured from 0 PPM up to 1.5 PPM (r=0.79) with NO2 undetectable. DISCUSSION: Setting up a scavenging system that is functional can be difficult with some infant ventilators. In our experience, this has required minor modification to exhalation assemblies and/or circuits. Often, a canopy or other covering over the assembly is required, reducing visibility of the valve and its function. Additionally, applying a vacuum to the exhalation could inadvertently produce some untoward effect. CONCLUSION: Our data suggest the exposure levels of NO/NO2 may be less than previously thought and below the 20 PPM over 8 hours suggested standard. Scavenging exhaled gas, while somewhat simple may not be required in a large, well ventilated room. *averaged value