How is air measured?
The air in the Agilia Volumat dedicated infusion giving sets is measured by the Agilia VP MC infusion pump in two ways.
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As a total volume of air in a 15 minute period and as the volume of individual bubbles passing the air sensor.
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To understand this in more detail we first look to where the air sensor is located in the pump and how it measures the presence of air.
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The air sensor in the pump is located on the left-hand side as indicated by the yellow arrow.
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It works by sending an ultrasonic signal between two ceramic sensors as shown below.
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Fluid conducts the ultrasonic signal efficiently meaning the signal passes through any fluid with relative ease.
Air, however, will reflect the ultrasonic signal to an extent and cause the receiving ceramic sensor to register a decrease in the received signal.
This signal is measured in milliVolts.
Below is an example of an air bubble moving past the air sensor in an infusion set and the resulting signal recorded by the receiving ceramic sensor.
Based on the flow rate, the time for which the air sensor registers a decrease in the received signal, and a known infusion tubing inside diameter of 3.41mm the device can calculate how much air has passed the air sensor.
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For the infusion device in your department two air settings would have been agreed upon before the device was configured by our engineers and delivered to your hospital:
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The total volume of air allowed in a 15 minute period before the air alarm will sound
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The size of any air bubbles registered by the air sensor that should be recorded or ignored. As an example, the device can be set to ignore really small air bubbles and not include them in its running total of air measured within a 15 minute period.
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The range of air values allowed for both of these settings are summarised below:
To give you an idea as to what the bubbles you see in the Agilia Volumat dedicated infusion set equate to in volume we have created a graphic as shown below.
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1mL (1000μL) of air in the infusion set tubing is equivalent to approx. 14.3cm of tubing length.
To think about the air in a different way the below table summarises how long it will take for a 1cm air bubble to pass the air sensor in the Agilia VP MC infusion pump at different flow rates and be registered against the total volume of air recorded.
A 1cm air bubble represents 70 microLitres (μL) of air.
To learn about priming techniques, tips to minimise air in the line and use of the drop sensor have a read at the other sections available in the air menu by selecting the "BACK to air menu" button below.