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The effect of micropore filters on the aspiration test in epidural analgesia
1Shackleton Department of Anaesthetics, Southampton General Hospital.
Abstract:
Continuous epidural analgesia may be complicated by intravascular or subarachnoid injection of local analgesic, with disastrous consequences. One of the techniques described to prevent these complications is the aspiration test. It is the current standard of practice to employ a micropore bacterial filter for epidural infusions. We present an in vitro study of nine commercially available bacterial filters to determine whether or not the aspiration test could be reliably performed through them. Eight of the nine filters (except the Perifix, Braun) were found to be unreliable if air and liquid were both present in the system (air lock). The role of the aspiration test and the use of micropore filters in epidural analgesia are discussed, as are the implications and possible solutions in practice of this cause of failure of the test.
Insights
The aspiration test for epidural analgesia is often unreliable when using bacterial filters. Most filters fail if air and liquid are present, risking dangerous complications during epidural infusions.
Area of Science:
- Anesthesiology
- Pharmacology
- Medical Devices
Background:
- Continuous epidural analgesia is susceptible to complications like intravascular or subarachnoid injection.
- The aspiration test is a standard safety measure to prevent such complications.
- Micropore bacterial filters are commonly used in epidural infusions.
Purpose of the Study:
- To evaluate the reliability of the aspiration test when performed through commonly used micropore bacterial filters.
- To identify filter types that may compromise the effectiveness of the aspiration test.
Main Methods:
- An in vitro study was conducted.
- Nine commercially available micropore bacterial filters were tested.
- The ability to perform the aspiration test through these filters was assessed under conditions with both air and liquid present.
Main Results:
- Eight out of nine tested filters were found to be unreliable for the aspiration test.
- Filter unreliability occurred when both air and liquid were present, creating an 'air lock' scenario.
- The Perifix (Braun) filter was the only one that did not show this unreliability.
Conclusions:
- The widespread use of micropore bacterial filters may compromise the reliability of the aspiration test in epidural analgesia.
- This finding has significant implications for patient safety during epidural procedures.
- Alternative methods or filter modifications may be needed to ensure the effectiveness of the aspiration test.
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