Potential hazards associated with microbial contamination of in-line filters during intravenous therapy

Investigation of in-line filter replacement intervals for infusion

BACKGROUND

In-line filters in peripheral and central venous catheters are used to remove bacterial cells mechanically. A recent study indicated an extension of the use of infusion sets to 7 days. There is no evidence regarding replacement intervals for in-line filters.

AIM

To test in-line filters that were used continuously for 7 days in order to investigate their ability to remove bacteria and assess the flow rate.

METHODS

Three different in-line filters were attached to an ELNEOPA-NF No. 2 premixed infusion bag of intravenous hyperalimentation, into which Staphylococcus epidermidis ATCC12228 or Escherichia coli ATCC25922 was inoculated. These experiments were compared with a control infusion. The infusion was dropped at a flow rate of 40 mL/h and replaced at 24-h intervals for 7 days. Samples were collected 24 h after drop initiation.

FINDINGS

S. epidermidis was not detected in droplets between Days 1 and 6, but In-line filters 1 and 2 showed droplets containing 6-10 colony-forming units/mL on Day 7. E. coli was not detected in any of the filters after 7 days of continuous use. Flow rates <40 mL/h were observed on Day 7 for In-line filter 3 in studies of S. epidermidis, and on Days 4 and 3 for In-line filters 2 and 3, respectively, in studies of E. coli.

CONCLUSION

This study revealed differences in bacterial removal and flow rates under high inoculation between the three in-line filters tested. It is suggested that in-line filters can be used continuously for a maximum of 6 days, and reductions in flow rate after 48 h of continuous use should be noted carefully.

Gram-negative bacterial lipopolysaccharide retention by a positively charged new-generation filter

Removing endotoxins is an important target in the pharmaceutical industry and in clinical practice. A filter introduced into an intravenous line prevents microbiological contamination, but to date no filters have retained bacterial endotoxins. In our study, we assayed a new-generation filter which is able to capture endotoxins from solutions.

Bacterial colonization and endotoxin contamination of intravenous infusion fluids

Bacterial colonization and endotoxin contamination of intravenous infusion fluids and catheter systems were examined in a surgical intensive care unit. Nineteen consecutive patients were randomly assigned to 48 h (N = 8) or 96 h (N = 11) change of infusion systems. Fluid from infusion bottles (51), infusion bottles plus burettes (102) and catheter systems (104) was cultured quantitatively for aerobic and anaerobic bacteria. Swabs (362) were taken from three-way stopcocks before and after the in-line infusion filters. Total and free endotoxin levels in infusion fluids were measured by quantitative chromogenic Limulus assay. The overall rate of bacterial colonization of bottles/burettes was 7.8% at 48 h and 15.7% at 96 h, while colonization rates of catheter fluid were 34.0% and 24.1%, respectively (n.s.). These high rates of colonization, despite regularly reinforced hand disinfection practices, may be explained by the high frequency of manipulations of the catheter systems, during acute interventions in emergency situations. Cell-bound endotoxin was found in 8.8% of the samples, but only 2.5% of the samples contained free endotoxin. The data support the use of in-line infusion filters, with bacterial-retaining property; however, these filters need not have endotoxin-retaining properties.

Intravenous filters, panacea or placebo?

Proponents of intravenous filters claim that they remove bacterial contaminants, particulate matter, air emboli and reduce the incidence of phlebitis. From unstructured observation by the author at a large general hospital not using filters it was concluded that the incidence of complications was no greater than at a hospital having a policy for using these filters. Despite the introduction of a filter that claims to retain endotoxin for up to 96 h, filters are still misused, over used or unused in different departments of the same hospital. This paper examines the literature that supports and criticizes the advantages and disadvantages of using such filters. The research is reviewed to ascertain whether the widespread use of filters is justified and whether they effectively reduce or prevent the complications of intravenous therapy. The paper reviews the causes and incidence of complications of intravenous therapy and alternative methods used for reducing these complications. The evidence shows conflicting results and argues that complications are inevitable despite the use of filters or careful medical action. The manufacturer's claims are supported by a plethora of literature but discrepancies are evident and the author remains unconvinced of their widespread use in today's fragile economic climate when the cost of treating the adverse effects of intravenous therapy is considered.

Hazards of parenteral treatment: do particles count?

After prolonged parenteral nutrition a 12 month old infant died with pulmonary hypertension and granulomatous pulmonary arteritis. A review of necropsy findings in 41 infants who had been fed parenterally showed that two of these also had pulmonary artery granulomata, while none of 32 control patients who died from sudden infant death syndrome had similar findings. Particulate contaminants have been implicated in the pathogenesis of such lesions and these were quantified in amino acid/dextrose solutions and fat emulsions using automated particle counting and optical microscope counting respectively. Parenteral feed infusions compounded for a 3000 g infant according to standard nutritional regimens were found to include approximately 37,000 particles between 2 and 100 microns in size in one day's feed, of which 80% were derived from the fat emulsion. In-line end filtration of intravenous infusions may reduce the risk of particle associated complications. A suitable particle filter is required for use with lipid.

Infection control of parenteral nutrition solutions

Microbial contamination of parenteral nutrition solutions is a preventable cause of in patients receiving nutrition support. The components of the parenteral nutrition solutions have variable microbial growth potential. Crystalline amino acid and dextrose solutions are poor growth media for bacteria but may support fungal growth. Lipid emulsions provide an excellent medium for growth of bacteria and fungal species. Total nutrient admixtures will support microbial growth better than standard parenteral nutrition solutions will but less well than will lipid emulsion alone. Control of infection related to contaminated infusate depends on compounding procedure, quality control, appropriate storage, and procedures to prevent in-use contamination. Guidelines are presented for the preparation and administration of parenteral nutrition infusates that will minimize microbial contamination.

Use of endotoxin retentive intravenous filters with paediatric total parenteral nutrition solutions

We studied the retention of endotoxin released in a clinically relevant form by senescent bacteria during filtration of amino acid-based total parenteral nutrition (TPN) solutions by the PALL Intravenous Set Saver Filter (ELD96). The ELD96 was shown to be capable of providing an effluent free of detectable endotoxin (less than 0.125 endotoxin unit-equivalents/ml) when challenged with 10(6) total cells of Pseudomonas aeruginosa during simulated clinical TPN infusion. Parallel control experiments showed that endotoxin was released from the test organism and penetrated through conventional intravenous (i.v.) solution filters.

Endotoxin removal by end-line filters

Four commonly used end-line filters, one with a charge-modified hydrophilic nylon filter (ELD96; Pall Biomedical Ltd., Portsmouth, United Kingdom), one with an unmodified nylon filter (FAE020; Pall Biomedical), and two with hydrophilic cellulose ester filters (Ivex-HP, Millipore Corp., Bedford, Mass.; Sterifix, Braun-Gelman, Brussels, Belgium), were evaluated for their endotoxin-removing capacity in saline and 5% glucose. Natural endotoxins derived from Escherichia coli 8739 and the lipopolysaccharide mutant Pseudomonas aeruginosa PA220-R2 and a purified E. coli serotype O111:B4 lipopolysaccharide preparation were used to challenge the four end-line filters. No endotoxin-removing capacity was observed for the Ivex-HP and Sterifix filters. Both the FAE020 and the ELD96 end-line filters showed excellent endotoxin-eliminating capacities in 5% glucose. Increasing the NaCl concentration in 5% glucose, however, greatly reduced the endotoxin-removing efficiency of especially the ELD96 filter for the purified E. coli lipopolysaccharide preparation. Obviously, both the nature of the endotoxin and the ionic strength of the solution had a major influence on the endotoxin end-line filtering efficiency.

Bacteriologic contamination of intravenous infusion delivery systems in an intensive care unit

Seventy intensive care unit patients were admitted to a double-blind prospective study to determine the level of contamination associated with the admixture and administration of intravenous solutions and whether intravenous filtersets prevented bacteremia. Patients were randomly assigned a 0.22 micron filterset (real filter) or a filter cartridge without a 0.22 micron membrane (blank filter) on all possible intravenous lines. Forty-six (14.1 percent) real filtersets and 38 (11.3 percent) blank filtersets were found to be contaminated, and overall 30 patients (42.4 percent) were found to have extrinsically contaminated intravenous administration systems at least once during the study. Bacterial adherence to the plastic cartridge was demonstrated to be responsible for culture-positive blank filtersets. Staphylococcus epidermidis was the organism most frequently isolated from real and blank filtersets. Epidemiologic surveillance identified 10 patients with blank filtersets and three patients with real filtersets with clinically significant hospital-acquired bacteremias during the study period. It is concluded that a significant level of extrinsic contamination of intravenous infusion delivery systems occurred on the intensive care unit; documented clinically significant nosocomial bacteremias occurred less often in those patients who had a 0.22 micron bacterial retention filter on all possible intravenous lines.