Final inline filtration for intravenous infusions: a prospective hospital study

Comparative study between a gravity-based and peristaltic pump for intravenous infusion with respect to generation of proteinaceous microparticles

Subvisible particles generated during the preparation or administration of biopharmaceuticals might increase the risk of immunogenicity, inflammation, or organ dysfunction. To investigate the impact of an infusion system on the level of subvisible particles, we compared two types of infusion set based on peristaltic movement (Medifusion DI-2000 pump) and a gravity-based infusion system (Accu-Drip) using intravenous immunoglobulin (IVIG) as a model drug. The peristaltic pump was found to be more susceptible to particle generation compared to the gravity infusion set owing to the stress generated due to constant peristaltic motion. Moreover, the 5-µm in-line filter integrated into the tubing of the gravity-based infusion set further contributed to the reduction of particles mostly in the range ≥ 10 µm. Furthermore, the filter was also able to maintain the particle level even after the pre-exposure of samples to silicone oil lubricated syringes, drop shock, or agitation. Overall, this study suggests the need for the selection of an appropriate infusion set equipped with an in-line filter based on the sensitivity of the product.

Particulate Matter in Injectable Drugs: Evaluation of Risks to Patients

One of the fundamental principles guiding the pharmaceutical quality of parenteral products is to prevent injecting contaminants from microbiological, chemical or physical sources. It is just as difficult to ensure the absence of chemical and particulate contaminants in injectable products as it is to weigh up the microbiological risk. The problem of particulate matter is mainly related to the preparing and administrating of injectable drugs rather than through the contamination of marketed products. Particulate contamination also arises

Intravenous in-line filters for preventing morbidity and mortality in neonates

BACKGROUND

Venous access is an essential part of caring for the sick neonate. However, problems such as contamination of fluids with bacteria, endotoxins and particulates have been associated with intravenous infusion therapy. Intravenous in-line filters claim to be an effective strategy for the removal of bacteria, endotoxins and particulates associated with intravenous therapy in adults and are increasingly being recommended for use in neonates.

OBJECTIVES

To determine the effect of intravenous in-line filters on morbidity and mortality in neonates.

SEARCH METHODS

We used the standard search strategy of the Cochrane Neonatal Review Group. We searched the electronic databases MEDLINE (from 1966 to May, 2015), EMBASE (from 1980 to May, 2015), CINAHL (from 1982 to May 2015) and the Cochrane Central Register of Controlled Trials (CENTRAL; 2015, Issue 5). We did not impose any language restrictions. Further searching included cross references, abstracts, conferences, symposia proceedings, expert informants and journal handsearching.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) or quasi-RCTs that compared the use of intravenous in-line filters with placebo or nothing in neonates.

DATA COLLECTION AND ANALYSIS

We followed the procedures of the Cochrane Neonatal Review Group throughout. We checked titles and abstracts identified from the search. We obtained the full text of all studies of possible relevance. We independently assessed the trials for their methodological quality and subsequent inclusion in the review. We contacted authors for further information as needed. Statistical analysis followed the procedures of the Cochrane Neonatal Review Group.

MAIN RESULTS

There were four eligible studies that recruited a total of 704 neonates. This review of low to very low quality evidence found that the use of in-line filters compared with unfiltered fluids for intravenous infusion had no statistically significant difference in effectiveness on overall mortality (typical RR 0.87, 95% CI 0.52 to 1.47; typical RD -0.01, 95% CI -0.06 to 0.04; two studies, 530 infants), proven and suspect septicaemia (typical RR 0.86, 95% CI 0.59 to 1.27; typical RD -0.02, 95% CI -0.09 to 0.04; two studies, 530 infants), or other secondary outcomes (including local phlebitis and thrombus, necrotising enterocolitis, duration of cannula patency, length of stay in hospital, number of catheters inserted and financial costs).

AUTHORS' CONCLUSIONS

There is insufficient evidence to recommend the use of intravenous in-line filters to prevent morbidity and mortality in neonates.

Guideline for Prevention of Intravascular-Device–Related Infections

The “Guideline for Prevention of Intravascular Device-Related Infections” is designed to reduce the incidence of intravascular device-related infections by providing an over view of the evidence for recommendations considered prudent by consensus of Hospital Infection Control Practices Advisor y Committee (HICPAC) members. This two-part document updates and replaces the previously published Centers for Disease Control's (CDC) Guideline for Intravascular Infections (Am J Infect Control1983;11:183-199). Part I, “Intravascular Device-Related Infections: An Over view” discusses many of the issues and controversies in intravascular-device use and maintenance. These issues include definitions and diagnosis of catheter-related infection, appropriate barrier precautions during catheter insertion, inter vals for replacement of catheters, intravenous (IV) fluids and administration sets, catheter-site care, the role of specialized IV personnel, and the use of prophylactic antimi-crobials, flush solutions, and anticoagulants. Part II, “Recommendations for Prevention of Intravascular Device-Related Infections” provides consensus recommendations of the HICPAC for the prevention and control of intravascular device-related infections. A working draft of this document also was reviewed by experts in hospital infection control, internal medicine, pediatrics, and intravenous therapy. However, all recommendations contained in the guideline may not reflect the opinion of all reviewers.

Drug retention by inline filters--effect of positively charged polyethersulfone filter membranes on drug solutions with low concentration

OBJECTIVE

The use of infusion filters in pediatrics is controversially discussed. Their application is an excellent opportunity to prevent complications, but there are researchers, who do not see any advantage in using inline filters. This paper describes the interaction of five different drugs with a positively charged as opposed to an uncharged polyethersulfone (PES(+) versus PES(0)) membrane.

METHODS

To measure the extent and the mechanism of interaction, PES(+) versus PES(0) membranes and furosemide sodium, potassium canrenoate, digitoxin, digoxin and adenosine, each 30μmol/l, were investigated. Salt ions with different hydrodynamic radii and different concentrations have been used in the eluents.

RESULTS

During furosemide sodium and potassium canrenoate filtration with PES(+), the onset of UV absorption depends on the electrolyte concentration in the eluent: the lower the electrolyte concentration the later the onset of UV absorption. A correlation between the hydrodynamic volume of the different salt ions used and the onset of UV absorption could be proven for both substances: The larger the hydrodynamic volume of the extrinsic ion, the later the onset of the UV absorption if the same electrolyte concentration was used. Due to a higher structural density of PES(+) than PES(0) a delayed onset of UV absorption during filtration of digitoxin and digoxin with the PES(+) membrane could be observed. No correlation between the hydrodynamic volume of the different salt ions used and the onset of UV absorption could be seen. With adenosine neither the filter type nor the electrolyte concentration or the hydrodynamic volume of the salt ions had an influence on the onset time of absorption.

CONCLUSION

The results obtained with the anionic drugs investigated are particularly relevant if low drug concentrations in a saltless infusion solution are applied in combination with a charged filter membrane. Therefore, for each infusion formulation, a careful selection of the filter material is essential.

Prolonging the survival of peripheral infusion sites in neonates with low dose heparin

The effect was studied of adding heparin to 10 per cent dextrose and to total parenteral nutrition (TPN) solutions infused into peripheral veins of premature babies. The median survival times of sites receiving 10 per cent dextrose and TPN solutions without heparin were 37 and 22 hours, respectively. Addition of 0. liu/ml heparin had little effect whereas adding 0.25iu/ml increased survival times to 48 and 32 hours, respectively. Adding 0.5iu/ml heparin increased survival times to 67 and 68 hours, and with liu/ml they rose further still, to 69 and 83 hours, respectively. These data suggest that 0.5iu/ml may be sufficient to prolong the survival of peripheral intravenous sites in premature babies.

Should in-line filters be used in peripheral intravenous catheters to prevent infusion-related phlebitis? A systematic review of randomized controlled trials

BACKGROUND

In this systematic review, we assessed the effect of in-line filters on infusion-related phlebitis associated with peripheral IV catheters. The study was designed as a systematic review and meta-analysis of randomized controlled trials. We used MEDLINE and the Cochrane Controlled Trial Register up to August 10, 2009.

METHODS

Two reviewers independently assessed trial quality and extracted data. Data on phlebitis were combined when appropriate, using a random-effects model. The impact of the risk of phlebitis in the control group (baseline risk) on the effect of in-line filters was studied by using meta-regression based on the bivariate meta-analysis model. The quality of the evidence was determined by using the GRADE (Grading of Recommendations Assessment, Development, and Evaluation) method.

RESULTS

Eleven trials (1633 peripheral catheters) were included in this review to compare the effect of in-line filters on the incidence of phlebitis in hospitalized patients. Baseline risks across trials ranged from 23% to 96%. Meta-analysis of all trials showed that in-line filters reduced the risk of infusion-related phlebitis (relative risk, 0.66; 95% confidence interval, 0.43-1.00). This benefit, however, is very uncertain, because the trials had serious methodological shortcomings and meta-analysis revealed marked unexplained statistical heterogeneity (P < 0.0000, I(2) = 90.4%). The estimated benefit did not depend on baseline risk.

CONCLUSION

In-line filters in peripheral IV catheters cannot be recommended routinely, because evidence of their benefit is uncertain.

Intravenous in-line filters for preventing morbidity and mortality in neonates

BACKGROUND

Venous access is an essential part of caring for the sick neonate; however, problems such as contamination of fluids with bacteria, endotoxins and particulates have been associated with intravenous infusion therapy. Intravenous in-line filters claim to be an effective strategy for the removal of bacteria, endotoxins and particulates associated with intravenous therapy in adults and are increasingly being recommended for use in neonates.

OBJECTIVES

To assess whether in-line filters on intravenous lines prevent morbidity and mortality in neonates.

SEARCH STRATEGY

Searches were made of the electronic databases MEDLINE (from 1966 to September 2005), EMBASE (from 1980 to September 2005), CINAHL (from 1982 to September 2005) and the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, Issue 3 2005 ). There was no language restriction. Further searching included cross references, abstracts, conferences, symposia proceedings, expert informants and journal handsearching.

SELECTION CRITERIA

Randomized or quasi-randomized controlled trials that compared the use of intravenous in-line filters with placebo or nothing in neonates were included in the review.

DATA COLLECTION AND ANALYSIS

The procedures of the Cochrane Neonatal Review Group (CNRG) were followed throughout. Titles and abstracts identified from the search were checked by the review authors. The full text of all studies of possible relevance were obtained. The review authors independently assessed the trials for their methodological quality and subsequent inclusion in the review. Statistical analysis followed the procedures of the Cochrane Neonatal Review Group. Dichotomous data is expressed as relative risk and 95% confidence intervals, and risk difference and 95% confidence intervals.

MAIN RESULTS

There were three eligible studies, which recruited a total of 262 neonates. For most of the outcomes for this review, only one study of 88 neonates contributed eligible data. This review found no significant effect of in-line filters in any of the reported outcomes of overall mortality, proven and unproven septicaemia, phlebitis, necrotizing enterocolitis, duration of cannula patency, number of catheters inserted and financial costs.

AUTHORS' CONCLUSIONS

There are insufficient data to determine whether or not the use of intravenous in-line filters prevent morbidity and mortality in neonates. The wide confidence intervals on outcomes indicate the imprecise estimates of treatment effect due to the small numbers of patients and events.

Prescripción y elaboración de nutrición parenteral en los hospitales españoles

OBJECTIVE

To identify habits related to prescription and preparation of parenteral nutrition in Spain and their adequacy to current recommendations.

METHOD

A questionnaire was administered in order to collect information about the characteristics of diets used at each hospital and the way they were prepared. The questionnaire was available through the web page of the Spanish Society of Hospital Pharmacy.

RESULTS

Forty five hospitals answered the questionnaire. More than 90% of the hospitals reported that they used diets with a fixed or standard composition and 66.6% reported that they bought diets available in the market with a defined composition. Fifty seven point five per cent of the hospitals always prepared "all in one" parenteral nutrition and 37.5% prepared them only for adults. A 5% provided the lipids separately, both for adults and for children. Forty five per cent of the hospitals reported that they did not use organophosphates as source of phosphate. Almost 60% alternate the introduction of vitamins and trace elements. Differences were also found regarding the type of lipids provided and the use of filters. Most hospitals used multi-layer bags and photoprotection.

CONCLUSIONS

There is quite a lot of diversity in the patterns of prescription and preparation of parenteral nutrition in our country. Further consensus documents should be written about these topics.

Contamination Control in Nursing With Filtration

Filters often are viewed as screens with openings smaller than the particles intended to be removed by a process technically known as direct interception. However, filter manufacturing embraces far more advanced technological approaches, with an evolution toward selective removal of cells or soluble constituents from complex physiologic solutions. An appreciation of filtration development makes it easy to understand how differently manufactured filters with the same claims may not perform identically. This article focuses on the filtration of intravenous solutions and point-of-use hospital water.

Reducing infusion phlebitis in Singapore hospitals using extended life end-line filters

Two studies were conducted to investigate the impact of the 4-day end-line filter used to treat infusion phlebitis in Singapore. In the first study, conducted in 1997, 200 patients received IV antibiotics and chemotherapy. In the first 100 patients, end-line filters were not used during the infusions. This resulted in a phlebitis rate of 31%. In the second group of 100 patients, end-line filtration was used, resulting in a phlebitis rate of 5%. In 2000, a second study was conducted, measuring the outcome of end-line filtration versus no end-line filtration use. In this case, phlebitis developed in 35% of 100 patients receiving antibiotics, as compared with 8% of 394 patients with the use of 4-day end-line filtration. These are the first such studies performed in Southeast Asia that highlight identical benefits, namely the reduction of phlebitis by elimination of particulates, in two separate patient populations. End-line filtration, when used to deliver antibiotics and chemotherapy, will result in significantly fewer cases of infusion phlebitis, reduce the cost of delivering IV antibiotics and chemotherapy, increase nursing efficiency, and ultimately improve patient comfort.

Particulate matter contamination of intravenous antibiotics aggravates loss of functional capillary density in postischemic striated muscle

Through the increased use of less expensive and counterfeit medicines, the contamination of parenteral fluids and drugs by particulate matter poses an increasing health hazard worldwide. However, the mechanism of action of such contamination has never been conclusively demonstrated. We have systemically injected the particles contained in three different 1-g preparations of the antibiotic cefotaxime into hamsters and visualized the functional capillary density in striated skin muscle, using intravital fluorescence microscopy. Injection of particles from either of the three preparations did not affect capillary perfusion in normal muscle (n = 3 hamsters, each). However, injection of particles from two generic drug preparations, but not the original preparation or the saline control, significantly reduced capillary perfusion in muscle tissue that had previously been exposed to 4 h of pressure-induced ischemia and 2 h of reperfusion (n = 9 hamsters per group). Histological sections demonstrated birefringent particles mechanically obliterating the microcirculation of the striated muscle. The loss of capillary perfusion due to particle injection or injection of standardized microspheres was dependent on the extent of ischemia/reperfusion-induced muscle injury, with more capillaries lost in the more severely compromised muscle areas. These findings suggest that particle contaminants may not pose a major threat in intact tissue, but may severely compromise tissue perfusion in patients with prior microvascular compromise of vital organs (i.e., after trauma, major surgery, or sepsis) and thus predispose to complications such as acute respiratory distress syndrome or multiple organ failure.

I.v.-related phlebitis, complications and length of hospital stay: 1

This article, the first of two-parts, addresses the growing problem of intravenous-related phlebitis in hospitalized patients, and the resultant personal and financial costs to both patient and hospital. Literature on the various types of phlebitis, the factors that increase the patient's risk of developing phlebitis, clinical indicators and severity grading scales, and the complications of phlebitis are examined. Awareness of such factors is considered instrumental in minimizing the incidence of intravenous-related phlebitis. The second article in this series will present a study of 90 patients from a large teaching hospital, which was conducted to determine the incidence and severity of intravenous-related phlebitis, risk factors, associated complications, and the related length of hospital stay. The implications of the results for current and future nursing care of patients receiving i.v. therapy will be discussed, and recommendations for safe practice will be made.

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.

Assessment of in-line filters to prolong the life of intravenous cannulae in cystic fibrosis patients

Twelve patients with cystic fibrosis received 12 courses of intravenous antibiotics, each over 10-14 days, both with and without the use of an extended-life disposable filter. The design of the trial was to replace the Venflon cannulae as they became non-patent and inserting a filter on alternate occasions. Thus each patient acted as her/his own control. Comparison of times during which cannulae remained patent showed a 50% improvement with use of a filter for 4 patients and no change for 7 patients. There was no significant difference associated with the use of a filter for the group as a whole but our small sample size excludes modest improvements.

Peripheral intravenous line survival and phlebitis prevention in patients receiving intravenous antibiotics: heparin/hydrocortisone versus in-line filters

OBJECTIVE

To compare the use of in-line filtration with the addition of heparin/hydrocortisone (hep/hc) to the infusate for both phlebitis prevention and intravenous (i.v.) line survival in peripheral i.v. catheters. This study was specific for a patient group receiving prolonged courses of i.v. antibiotics. Analysis of the two endpoints for conventional short i.v. catheters (short lines) versus long (30 cm) i.v. catheters (long lines) was also performed.

METHODS

Patients with cystic fibrosis receiving intermittent i.v. antibiotics were randomly allocated to receive their drugs either through an in-line filter using a drug-free infusate or with no filter and an infusate containing heparin 500 units and hydrocortisone 10 mg/L. Infusion sites were assessed daily.

RESULTS

Both the hep/hc and filter groups were similar in terms of phlebitis incidence and i.v. line survival when analyzed separately for both short and long lines. Long lines displayed markedly prolonged survival times and reduced phlebitis compared with short lines.

CONCLUSIONS

The effectiveness of i.v. filters in excluding the large particle load introduced by i.v. antibiotics and hence in reducing the subsequent phlebitis makes them a useful alternative to the use of hep/hc. The use of filters in this patient group may offer advantages in terms of ease of use and a possible decrease in hep/hc-related problems. Long lines offer practical advantages over short lines for patients requiring longer term i.v. access.

First choice for total parenteral nutrition: the peripheral route

Historically, total parenteral nutrition (TPN) has been administered by the central venous route because of the rapid development of thrombophlebitis when TPN solutions are administered into peripheral veins. The insertion and placement of central venous catheters is, however, associated with morbidity and mortality and is the main cause of TPN-related complications. By avoiding central venous catheterization, TPN can be made safer. Current awareness about the pathophysiology of peripheral vein thrombophlebitis and the use of a number of techniques that prevent or delay onset of peripheral vein thrombophlebitis mean it is now possible to administer TPN via the peripheral route. These techniques and changes in the practice of TPN in recent years (eg, reduction of caloric loads and use of lipid emulsions) mean peripheral parenteral nutrition is a technique that is now applicable to the majority of hospitalized, nutritionally compromised patients for whom intravenous feeding is anticipated for less than 10 to 14 days.

Studies in phlebitis: detection and quantitation using a thermographic camera

A new method for the detection of acute phlebitis in superficial veins is investigated. A thermographic camera is utilized for the quantitation of temperature changes in a rabbit ear model. A control group receiving no injection is compared against each of five treatment groups receiving these commercially available parenterals: amiodarone hydrochloride, phenytoin sodium, mechlorethamine hydrochloride, cephalothin sodium, and diazepam. The vehicles of the above-mentioned drugs as well as several commonly used organic cosolvents are also investigated. Local tissue responses to the parenteral challenges are measured and a good correlation between the visual and the thermographic data was seen.

Failure of intravenous infusions from extravasation and phlebitis

A survey was done to compare the rates at which phlebitis and extravasation cause failure of intravenous infusions lasting more than 24 hours. Slightly more infusions failed due to phlebitis than to extravasation but extravasation did not occur earlier or later than phlebitis or differ significantly from it in frequency when different types of infusions were compared. Univariate life table analysis indicated that the co-infusion of blood, potassium or cephalosporin antibiotics slightly increased and that higher flow rates markedly increased failure, that infusions including continuous heparin and steroids had markedly decreased failure, and that failure was not significantly affected by other antibiotics or by differences in sex, age, location of infusion site or time of year. Multivariate analysis showed that the above differences were statistically significant only for infusion rate, heparin and steroids.

Saving money with effective in-line filters

The Intensive care unit at Umeå Regional Hospital has during the past year, 1988, used PALL ELD 96 inline-filters on all patients with a central venous catheter. Two different time-periods were investigated, one when inline-filters were used and one without in-line filters. By counting the amount of intravenous disposables that were used and with TISS registration (therapeutic intervention scoring system) which is registered daily on all patients, cost and savings were derived 'per occupied bed day'. The study shows that through using in-line filters which are changed every 96 hours we may save approximately 35,000 pounds every year.

Vascular-access infections in hospitalized patients

Vascular catheters are a common source of nosocomial infections, although many of these infections are potentially preventable. A long duration of catheterization, multiple catheter manipulations, the inexperience of some inserters, use of transparent plastic dressings, violations of aseptic technique, the use of multilumen catheters, and inadequate sterilization of reusable pressure transducers all increase the risk of these infections. The only interventions that have been proved to reduce the risk are standardized insertion and maintenance technique by an intravenous-therapy team, preinsertion skin preparation with chlorhexidine gluconate, and the use of topical antibiotics at the insertion site. The goal of the physician should be to prevent catheter infection, because the treatment of established infection can be difficult and costly. Treatment must be individualized for each patient on the basis of the clinical presentation and the causative organism.

Particulate contaminants of intravenous medications and infusions

Particulate contamination in small volume parenteral medications has been studied and compared with that found in a selection of large volume infusions. Particle counts in 39 commonly used small volume medications and 7 large volume infusions were performed by an automated light blockage method (HIAC) or by optical microscopy. Based on these results and a random survey of drug therapy of intensive care patients, it is concluded that the contribution of intravenous medications to the total particle load received by such patients is likely to be many times greater than from infusion fluids. Until firm evidence regarding the harmful systemic effects of drug particles is available and the manufacturing regulations adjusted appropriately, final in-line filtration of infusions immediately proximal to the intravenous cannula should be considered when drugs are being given intravenously.

125I-fibrinogen uptake on peripheral venous cannulas: a comparison between different cannula materials and coatings

Using a similar technique as 125I-Fibrinogen uptake test for detection of deep venous thrombi, the radioactivity over cannulas inserted into veins on the dorsal aspect of the hands was measured 1, 2, 4 and 24 h after insertion. In three groups of 10 postoperative patients it was by random allocation inserted on one side a siliconized tetrafluorethylene cannula and on the other side one of either: a nonsiliconized tetrafluorethylene cannula and on the other side one of either: a nonsiliconized tetrafluorethylene, a heparinized tetrafluorethylene or a fluorethylenpropylene cannula. The same volume and type of infusion was given in both cannulas. No difference in protein deposition was seen between siliconized and nonsiliconized tetrafluorethylene. A tendency of lower protein deposition, especially at 24 h on heparinized tetrafluorethylene was found. The fluorethylenpropylene cannulas had both over cannula and adjacent vein higher protein deposition at all measurements compared to the siliconized tetrafluorethylene cannula (p less than 0.01). The results implicate that fluorethylenprophylene could induce a higher incidence of thrombophlebitis than tetrafluorethylene cannulas.

Use of transdermal glyceryl trinitrate to reduce failure of intravenous infusion due to phlebitis and extravasation

Self-adhesive patches which release glyceryl trinitrate at a slow continuous rate or placebo patches were applied to the skin of patients distal to intravenous infusion sites in a double-blind manner. The frequency of infusion failure was three times lower with the glyceryl trinitrate than with placebo patches. The decrease was of similar magnitude whether failure was due to extravasation or phlebitis. Headaches were more common in patients with active patches but were relieved by simple analgesics.

Phlebitis and extravasation ("tissuing") with intravenous infusions

It is suggested that failure of infusions because of phlebitis or extravasation usually results from irritation of the endothelium by the infusate, inducing venoconstriction. If such venoconstriction prevents flow, then pressure which builds up in the vein will enlarge the hole in its wall made by the needle or cannula and so allow extravasation of fluid. Alternatively, partial constriction will cause the endothelium to be perfused with undiluted infusate, and this will aggravate the irritation and lead to phlebitis.