FAQ: IV Filters


Question 1: How do filters affect the incidence of phlebitis?

Answer 1:

Particles of undissolved material are present in very large numbers in many IV additives. They are also present in infusion fluids and are generated when glass ampoules are opened, rubber stoppers are pierced and IV administration systems are manipulated. By removing these particles, the irritation of the cannulated peripheral vein is dramatically reduced. This reduces the incidence of phlebitis and extends the cannula site life.


Question 2: How can we ensure the maximum reduction in phlebitis with this filter?

Answer 2:

Maximum benefit is gained by ensuring that all drugs and infusions that can be filtered are administered via the filter, including IV bolus injections.


Question 3: We use central lines and therefore do not see phlebitis. Could these patients also benefit from the use of a filter to remove particles?

Answer 3:

Particles in an unfiltered central line infusion may not produce immediately recognizable effects like phlebitis, but they have been associated with serious systemic effects. Granuloma formation in the lungs, raised white blood cell count and ESR have all been reported and some studies have suggested that particle contamination in infusions may contribute to the development of ARDS.


Question 4: End line filters do not prevent all bacteraemias, do they?

Answer 4:

End line 0.2 µm filters protect the patient from contamination arising in the IV fluid. It is possible however, that contamination can arise from other sources, e.g. at the insertion of the cannula and from wound infection, thus filters cannot prevent all bacteraemias. In a study of 70 intensive care patients, Quercia showed that there were only 3 bacteraemias in the filter group. This may reflect the number of bacteraemias in the control group. This may reflect the number of bacteraemias that result from manipulation of the IV system.

This is supported by further studies, Geiss and Lee showed respectively that 34% and 41% of extended life filters used on intensive care patients had trapped microbial contaminations thereby protecting patients. [Geiss H. Applied Hosp Hygiene 1988;3. Lee K. Infect Cont Nurses AssocConf 1994].

A French report showed that contamination during drug preparation, although uncommon, still occasionally occurs.

In addition to the retention of inadvertent microbial contamination from the set, since Pall Posidyne IV filters need changing only 96 hourly, the number of manipulations to the catheter hub is significantly reduced. A recent Dutch study showed a significant reduction in sepsis in neonates protected by Posidyne IV filters. [Presented at 8th European Congress of Clinical Microbiology and Infectious Diseases. Lausanne, Switzerland May 25-28 1977].


Question 5: You are advocating a 96 hr IV set change, but am I correct in stating that the general recommendation is still 24 hour?

Answer 5:

24 hour set change recommendations have been put forward in the past by various authorities such as national departments of health. These guidelines were made after several outbreaks of infection, such as the Devonport incident in the UK and a cluster of cases in the USA when contaminated IV solutions led to several fatal septicaemia cases. The recommendations acknowledge that IV systems and solutions can become contaminated in use and that routine daily changing would reduce microbial proliferation and infection potential. Since these guidelines were written, endotoxin retentive IV filters have been developed which can safely extend the life of IV sets to 96 hours by retaining extrinsic microbial contaminants and their associated endotoxins.


Question 6: Are the levels of endotoxin produced by inadvertent contamination with Gram-negative bacteria really pyrogenic?

Answer 6:

In the study by Holmes (J Clin Micro 1980;12:725-731), conventional end-line filters were contaminated upstream with about 100 Gram-negative bacteria. The level of endotoxin produced after 72 hours was up to 70 pg/mL which is equal to 350 EU/Litre. The threshold pyrogenic dose is defined as 5 EU/kg, so 1 litre of such a solution containing 350 EU would cause a fever in a 70 kg adult. Pall Posidyne filters have been shown to retain at least ten times this amount of endotoxin, giving a margin of clinical safety.


Question 7: I have heard that there are different kinds of endotoxin. What types are retained by the filters and how clinically important are these?

Answer 7:

Endotoxin is an integral part of the outer layer of Gram-negative bacteria. It is constantly shed into the bacteria's environment and is liberated in large amounts when the cell dies; this is seen when certain types of antibiotics are given, for example. The endotoxins from different groups of Gram-negative bacteria differ very slightly in their chemical detail, but all have the same basic form and biological effect. The endotoxin aggregate is in the form of a highly charged particle, this charge density causes irreversible binding to the Pall Posidyne filter material.

For some research work endotoxin is highly purified, by extracting it from the native particle using aggressive solvent to give a highly purified soluble preparation of a considerably smaller aggregate size. Its physical behavior is therefore changed and does not reflect the normal charged particle characteristics of native endotoxin released by bacterial cells. This purified "standard" endotoxin is therefore unsuitable for use in studies intended to evaluate performance in a clinical situation, since it would never be present in a clinical system. Several  studies have shown that Posidyne uniquely retains endotoxin in simulated clinical infusion for 96 hours.


Question 8: Do the filters eliminate all non-dissolved air?

Answer 8:

Yes, as long as the filters are properly primed they will vent all air arising on the set side via the vent holes.


Question 9: What steps should I take if I continue to see air bubbles downstream of the filter?

Answer 9:

First, open the administration set clamp slightly to reestablish flow. Then, gently tap the filter housing. When you observe that no bubbles are present, close the clamp. Finally, connect to the patient and regulate flow in the usual manner.


Question 10: Do the filters affect flow rates?

Answer 10:

The filters will not compromise flow rates used in IV administration of drugs and solutions. However, we would not recommend their use in the delivery of plasma expanders or other infusion solutions for emergency fluid resuscitation. Typically, with Posidyne ELD one can expect flow rates of 1 litre per hour for saline or 5% dextrose, under gravity with a 1 metre head pressure.


Question 11: Can we put drugs through the filter? Do any drugs bind?

Answer 11:

The filtration of small volume drugs is one of the major indicatons for the use of the filters. However, it should be noted that the following are contraindicated; blood, cellular blood components, suspensions, emulsions or medications that are not fully dissolved in the fluid being administered. If in doubt the hospital pharmacist should be consulted.

Posidyne filters have been in clinical use across the world for over a decade, for a wide range of intravenous medications and fluids.

Additionally, experimental work in our laboratories and elsewhere has confirmed the suitability of Posidyne filters for use with a wide range of drugs. It is understandable that this question should be asked concerning a positively charged membrane, endotoxin is retained by the filter as it is released by bacteria in aggregates that are highly charged particles. The high charge density causes strong irreversible binding to the filter. Negatively charged drugs conversely do not have sufficient charge density to bind.


Question 12: What would we do with emulsions and suspensions?

Answer 12:

Some Posidyne filters are available with a Y-injection site in the extension tubing. Preparations that are not able to pass through the filter (suspensions or emulsions) can be administered through this site or through a Y-connector placed below the filter. Nutrient emulsions and admixtures containing lipid can be filtered with the Pall Lipipor TNA filter.


Question 13: What happens to the filter if two incompatible drugs are inadvertently given through it?

Answer 13:

The filter protects the patient from the precipitate formed by two physically interacting drugs, which is, of course, a very large amount of particulate matter. It also alerts staff to the interaction because it stops flowing if a large precipitate is produced. This protects the patient from a bolus presentation of particulates and allows the interaction problem to be identified and solved.


Question 14: Why did some of the older type of filters occasionally crack?

Answer 14:

The first generation of filters were designed to "fail-safe" at the junction of the filter casing on the bag side of the membrane at a pressure of 10 psi or above. The membrane remains intact on the patient side of the filter casing thus preventing bolus delivery of particles and bacteria to the patient. Since that time pumps have become more sophisticated and many incorporate alarms to prevent over-pressurization. As a result the latest generation of IV filters still "fail-safe" but at a much higher pressure - about 30 psi.


Question 15: Can Posidyne filters be used to protect very low birth weight infants, for whom the flush volume for small doses of drugs must be kept to a minimum?

Answer 15:

The volume of the Posidyne NEO is 0.4 mL and a flush volume of 0.8 mL is recommended when administering drugs as boluses through the filter. This will be helpful with fluid restricted babies.

Some neonatal units add bolus injections into a running infusion of a compatible solution, to carry the bolus of drug in.


Question 16: Can the filter be used on central, as well as peripheral lines?

Answer 16:

Yes, patients with peripheral lines benefit from the protection of the filter, most noticeably because phlebitis is reduced and cannula site life extended, but central venous lines are protected by the filter against particle infusions that have systemic effects, notably on the lungs. The benefit of protection from inadvertent microbial contamination and associated endotoxins applies to central as well as peripheral venous lines. The risk of air embolism, which is greatest on central lines, is significantly reduced by the use of the filter.


Question 17: Can the filter be used for long-term IV therapy?

Answer 17:

Adult and pediatric patients who will require long term or even intermittent life-long intravenous therapy, such as those with cystic fibrosis, can benefit from the protection against particles from the very beginning of their treatment.


Question 18: Can the intravenous filter be used for intermittent IV therapy?

Answer 18:

Patients who are receiving intermittent IV infusion or injections can benefit from protection against the high level of particles that are found in some of the drugs typically given by IV 'push', such as antibiotics. Those receiving short infusions, who can be liberated from their giving set between infusions, can still enjoy the protection of the end-line filter. This can be achieved by leaving the filter attached to the patient's cannula, disconnecting the giving set from the filter and closing with a bung or cap. A cap should be placed in the inlet of the filter. The retention of the filter in this position on the cannula will protect against inadvertent contamination that may arise from connection and disconnection of giving sets, as infusions are required. Only one direct manipulation at the cannula hub will be required every 4 days, to change the filter.


Question 19: Can we expect to be able to offer cost effective IV therapy using this filter?

Answer 19:

Considerable savings in cost and nursing time have been noted by users of Pall Posidyne IV filters, many of these observations have been published. The most dramatic savings have been experienced in critical care areas, where IC therapy is very cost and time intensive. Patients receiving less intensive IV therapy can still receive cost effective care with the use of Posidyne filters, primarily since phlebitis is dramatically reduced. While reducing the overall risk to patients of developing this distressing condition.


Question 20: I have noticed a backflow of blood into the extension tubing. What causes this?

Answer 20:

Low (gravity) head height is a common cause of backflow. Low head height can occur as a result of a patient raising his/her are, the height of the IV bag being lowered during transit.


Question 21: The IV pump is alarming. Is it possible that this can be caused by the filter?

Answer 21:

IV solutions may contain large amounts of particulate that are not visible to the naked eye. Filters are used to remove these particulates from IV solutions before they are administered to the patient. Particulate buildup on the filter membrane can result in decreased flow rates, which in turn can trigger the pump alarm. To determine if this is the case, perform the following steps first, in order to eliminate other possible causes of the IV pump alarm being triggered:

  1. Inspect the tubing for kinks.
  2. Attempt to prime the filter in an effort to reestablish the flow rate by eliminating any downstream air bubbles.
  3. Check for low head height by either lowering the patient's arm, raising the IV bag, or both.

If none of the above steps corrects the pump alarm issue, change the filter.