MEDICAL GASES
Table 1. Chemical elements in the USP formula and postulate impacts of a breach condition. USP element (breach condition)
Impact considerations Oxygen content high (>23.5% v/v) Oxygen content low (<19.5% v/v) Carbon monoxide (>10 ppm)
Measured incidents of high oxygen content are thus far limited to <30% v/v and duration is typically less than five minutes. It is generally assumed that short term high oxygen release will homogenise through pipeline travel
Short term oxygen deprivation can have serious health effects in ventilated patients, especially neonates. Most anoxia monitors are set to alarm at 18% v/v, and there are cases on record of site produced medical air with O2
levels below this threshold
Sustained exposure to CO levels as low as 30 ppm can have serious long term health effects. Exposure to high levels of CO (ie >100 ppm) can be fatal. Haemoglobin is –240 times more attracted to CO than oxygen, so ensuring CO levels below the USP limit of 10 ppm is of paramount importance
Carbon dioxide (>500 ppm)
Elevated CO2 levels increase risk of respiratory failure or hyperventilation. The level at which CO2
Sites providing neonatal care may have greater concerns over CO2 the potential for a CO2
bolus release Humidity (> 5˚C pressure dewpoint* NOx (NO + NO2 >2.5 ppm)
Sulphur dioxide (>5 ppm) Oil (none detectable)
With strong evidence that a quality breach is expected, the consequences must be assessed. There are numerous studies confirming the health effects of common air pollutants, but none evaluate the effects on respiratory patients inhaling contaminated medical air. So we must start in a general sense by looking at the chemical elements in the USP formula and postulate impacts of a breach condition (see Table 1). Since medical air is a common adjunct
to respiratory therapies, it is recommended that the question set is expanded to include a few site specific queries: l Are the therapies involving medical air at this site typically of long (more than two hours) or short (less than two hours) duration?
l Do the medical devices typically involved monitor the USP chemical elements in the medical air prior to
Where potential for harmful exposure is low, the frequency of monitoring and method of off-spec prevention should be site determined IFHE DIGEST 2018
) bolus to cause short term oxygen deprivation as the bolus
exits the pipeline through a terminal unit. All desiccant air dryers are prone to sudden CO2
Humidity in the pipeline promotes bacterial growth and may harm sensitive medical devices. While moisture in medical air pipelines and related device damage is well documented, more research on pipeline bio-burden is necessary
Both NO and NO2 are respiratory irritants, and in volumes exceeding the USP limit
can lead to serious health problems or death A recognised toxic gas with serious health effects
Not considered given CSA restrictions on use of oil flooded compressor technologies *CSA Z7396.1 prescribed dewpoint, which exceeds USP requirements
patient inhalation and alarm in the event of an off-spec condition?
l Will the patient typically be able to voice concern if they sense a problem during treatment (for example, a strange smell)?
Answers can be used to formulate a site specific ‘potential for harmful exposure’.
1000 900 800 700 600 500 400 300 200 100 0
Table 2 assesses the most common therapies involving medical air.
Quality risk assessment Considering the information provided, it is necessary to return to the purpose of the quality risk assessment, which is to determine the frequency of sampling and analysis and the operating methods
becomes a concern seems dependent on patient type and co-morbidities. incursions given
n CO2
USP Limit
18 October 2016 (1,440 minutes)
Figure 1. A full day (one data point per minute) of CO2 The sine wave indicates the catch and release of CO2 depicts a quality breach whereby the measured CO2
measured in medical air. by a desiccant dryer and eclipses the pharmacopoeia
limit of 500 ppm. The severe peak suggests a bolus release, which presents a serious patient safety hazard.
85
PPM
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