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Patrick A Ball
Associate Professor of Clinical Pharmacy
School of Pharmacy
University of Auckland
The pharmacist making the call was concerned: one of the wards in the hospital had been using intravenous (IV) in-line filters for some time with very few problems, but recently a number of filter occlusions had occurred and the nursing staff of the unit were proposing that the use of filters be abandoned on the basis of “new recommendations from the CDC”.
The document from the Centers for Disease Control (CDC) in Atlanta (USA) to which the nurses were referring(1) is in fact focused on infection issues. It states that “there is no data to support their [in-line filters] efficacy in preventing infections associated with intravascular catheters and infusion systems” and that “in-line filters might become blocked […] thereby increasing the number of line manipulations and decreasing the availability of administered drugs.” However, because of its focus on infection, this document does not address the issue: what does a blocked filter mean?
Use of in-line filtration
Traditionally, in-line IV filtration has not been routine practice. Where it is used, it is seen as a means of trapping the intrinsic and extrinsic particulate contamination known to be present in all injection fluids, safely venting entrapped or “outgassed” air from the line and trapping microorganisms present within the solution.(2)
In practice, contaminated fluid is a relatively uncommon source of catheter infection, compared with skin, hub and line manipulation,(1) which also supports the less than enthusiastic view of the CDC document.
However, the use of in-line filtration needs to be considered in the context of the entire package: particles, air, microbiology and, increasingly, safety and quality assurance in parenteral therapy. The issues relating to the first three factors have recently been reviewed in a position statement from the British Pharmaceutical Nutrition Group (BPNG).(3) Filter occlusion needs further consideration.
Filters and safe parenteral therapy practice
In 20 years of laboratory research and clinical use of in-line filtration, this author has never seen a filter occlusion attributable to background particulate contamination or microbial contamination, despite testing solutions containing up to 10(12)cfu/ml in the laboratory.(4) All the cases of filter occlusion investigated were due to chemical precipitation or to serious destabilisation of an emulsion preparation (Ball PA, data on file). This leads to an important, and to date undervalued, role of the filter: the detection of problems and, therefore, the promotion of safety and quality assurance in parenteral therapy.
For many years the focus of investigation into medication errors has been to look at the mistakes of individuals. Somewhat belatedly, but now increasingly, the healthcare community has accepted that the environment, procedures and systems can contribute to errors.(5)
When in-line IV filtration is implemented in units, it is very common to find that filter occlusions occur. If a continuous record is maintained of, for example, what is being infused into the line, the drug additions that are made, the flushes used and the manipulations, it is usually possible to identify the cause of the problem and solve or avoid it.(6) In such cases, these occlusions represent problems with IV therapy practices that might otherwise have continued undetected.
Filter occlusion can be a valuable message even when safe practices have been established. This was clearly demonstrated in three recent cases of filter occlusion investigated in the laboratories of the School of Pharmacy at the University of Auckland (New Zealand).
A hospital children’s ward had been using in-line filters on parenteral nutrition lines for a number of years without incident. Their protocol involved a two-container system and two lines and two filters, linked by a “Y” connection. Recently, they started experiencing regular occlusions of lipid filters. The only product being infused into these lines was a commercial lipid emulsion, with no additions (ie, straight from the manufacturer’s container). Some filters had been returned to the filter manufacturer for examination but had suffered microbiological spoilage in transit and were inconclusive. On detailed questioning, the only change that could be identified was the component used for the “Y” connection. In the laboratory, it was possible to prove that “retrograde flow” was occurring, allowing the amino acid/glucose/electrolyte mixture to track back into the lipid line as far as the filter. A return to the previous connecting device removed the problem (Ball PA, submitted for publication).
The second case originated from another hospital. The unit had been using filters on a wide range of parenteral lines for several years without incident, but then began to experience occlusions. Following investigations, it was established that problems occurred with a preparation they used in preloaded syringes; this preparation was previously prepared in-house but had recently been outsourced. Although the supplier gave the preparation a 14-day shelf-life, on investigation a clear correlation was identified between the number of days the syringe had been stored before use and filter occlusion (Ball PA, submitted for publication).
In the third case, after a period using filters on all IV lines within the ward without problems, filter occlusions began to occur on a random basis. There was no identifiable change in products, procedures, equipment or suppliers. Although there had been a marked increase in occlusion incidents, no pattern emerged relating to particular combinations of medicines or diluents. A period of close monitoring was therefore proposed, where, as when filter use had originally been implemented, a record sheet would be kept documenting each manipulation of the system, with dates, times and the signature of the person involved. From the first day of the monitoring programme, no further occlusions occurred. It was concluded that the most likely explanation was that one or more staff in the unit had been breaching protocols and ceased to do so when at risk of being detected.(7)
These cases illustrate how problems can develop even when safe systems of working are well established. In addition to human error, problems can arise through equipment substitution and/or ingredient/supplier change. The issues discussed in these case studies would most probably have remained undetected if in-line filters had not been in use and become blocked. Filter occlusion should not be perceived as a problem of the filter. It is a message that something is wrong within the system and a call for investigation.
The position statement from the British Pharmaceutical Nutrition Group(3) reviews the background to this topic thoroughly and cites most of the important resources in this subject area. The author’s article entitled “Filtering the evidence”(2) discusses in more detail what the adverse effects of the infusion of particulates may be.
The major filter manufacturers and suppliers are also useful sources of information. Their global websites should be used to identify local suppliers
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