Heparin is routinely used to keep central venous catheters patent but is it the most effective flush solution? A systematic review was undertaken to find out
Barbara Jo Anderson, MSRN, NE-BC, isclinical director, Department of Medical/Surgical and Behavioral Health Nursing, Penn Presbyterian Medical Center, Philadelphia; Matthew D Mitchell, PhD, is coordinator, Center for Evidence-based Practice, University of Pennsylvania Health System; Kendal Williams, MD, MPH, is assistant professor of clinical medicine, University of Pennsylvania School of Medicine, and director, Center for Evidence-based Practice, University of Pennsylvania Health System; Craig Umscheid, MD, MSCE, is assistant professor of medicine, University of Pennsylvania School of Medicine, and co-director, Center for Evidence-based Practice, University of Pennsylvania Health System; Philadelphia.
Anderson BJ et al (2010) What is the evidence for heparin or saline flush to maintain the patency of central venous catheters? Nursing Times; 106: 16, early online publication.
Maintaining the function of central venous catheters is an important nursing responsibility, which should be carried out following the best available scientific evidence. We conducted a systematic review of the evidence on strategies to maintain patency of CVCs. Randomised trials found that flushing with heparin had no significant effect on catheter patency rates compared with flushing using saline. As a result we revised our catheter maintenance policy and now flush CVCs with saline.
Keywords: Central venous catheter, Evidence, Heparin
- This article has been double-blind peer reviewed
- Most existing guidelines for maintaining central venous catheters (CVCs) are not evidence based.
- There is insufficient evidence to conclude that a heparin flush is more effective than a saline flush.
- Flushing CVCs with heparin poses a risk of heparin induced thrombocytopenia.
- Pressure caps for CVCs may be associated with increased risk of bloodstream infection.
The use of heparin to flush central venous catheters (CVCs) has been accepted practice for decades. Heparin is thought to prevent clots developing in the catheter which would decrease or prevent flow through it and might be a potential locus for infection. Using CVCs carries risks and their insertion is usually undertaken for specific and necessary medical reasons. Preventing functional loss of the catheter is an essential component of nursing care for patients with these devices.
An evaluation of our policy for maintaining CVCs highlighted significant differences among members of our policy and procedure committee regarding the use of heparin flush to maintain catheter patency. Several members believed that research suggested using a normal saline flush was sufficient (American Association of Critical Care Nurses, 1993). But a review of the study found it involved flushing arterial catheters and was not applicable to our practice question. Since CVC maintenance varied throughout our organisation, with some using heparin and others using normal saline, we decided to look for evidence to guide our policy decision.
We asked the hospital librarian for a literature review on flushing central lines. At the same time we researched practice standards of professional nursing organisations whose specialty involved caring for patients with central venous access (Infusion Nurses Society, 2006; Camp-Sorrell and Cope, 2003; American Society for Parenteral and Enteral Nutrition, 2002). When recommendations were made, they called for heparin use at 100 units per millilitre. We were unable to identify any organisations recommending flushing with only normal saline.
We also examined the policies of other hospitals in the region. Most used heparin for central line flushing. Few policies cited evidence to support this choice, and one used a study of peripheral intravenous catheters which we did not consider applicable to CVC care. Despite anecdotal comments from the nursing community, there was little in organisational or local nursing standards to suggest we should stop using heparin flush.
Evidence based practice models allow us to consider expert consensus. We found experts in other areas of the country to ask about their practice. Although many had similar questions about using heparin versus normal saline, none could cite supporting evidence.
Use of positive pressure caps
Many policies we examined suggested using positive pressure caps on central venous access lines to eliminate the need for heparin. These caps provide pressure in IV lines when flush syringes are removed, preventing backflow of blood into the catheter and therefore preventing clotting. When we raised this as a potential solution, the infectious disease specialist physician whom we consulted had concerns, as anecdotal evidence was emerging about increased risk of infection with positive pressure caps and he recommended these should not be used.
Heparin induced thrombocytopenia
At this point in our investigation the evidence appeared to support using heparin to maintain catheter patency. However, we were not completely satisfied with our results as concerns about heparin induced thrombocytopenia (HIT) were raised (Swanson, 2007). HIT results from the formation of antibodies that target the heparin/PF4 antigen resulting in thrombosis, and the consequences can often be serious and life threatening to patients. Even the small amounts of heparin required for flushing a CVC can trigger HIT in susceptible patients (Muslimani et al, 2007). HIT is most common in patients undergoing cardiac surgery, and since our centre has patients in this group, doctors were concerned about any unnecessary heparin exposure. They wanted heparin flushing of central lines to stop.
Weighing the evidence
The policy and procedure committee faced a dilemma. We had an obligation to maintain necessary and often life sustaining CVCs. If we decided to stop using heparin this might result in clotting of catheters. We also had an obligation to prevent them from becoming infected, which can increase mortality risk, length of hospital stay and costs. Pressure caps might allow us to stop using heparin but appeared to expose patients to an increased risk of infection. Heparin induced thrombocytopenia was also a risk to patients and was a strong argument against using this drug.
The parent health system of our hospital established a Center for Evidence-based Practice (CEP) in 2006 to obtain and analyse clinical evidence and assist administrative and clinical departments with decision making. CEP reviews high cost new technologies and also reviews topics relating to processes of care in which cost considerations play little part. It worked with the nursing policy and procedure committee to investigate the practice of flushing CVCs and to evaluate competing factors to help determine what best practice should be.
After nursing leaders of the policy and procedures committee had presented the clinical problem, the CEP review began by outlining the clinical question using the PICO (patients, intervention, comparison, outcomes) framework. Terms used in the literature search followed from this definition. If the topic had not been clearly outlined at the beginning, evidence could have been missed in the literature search. Criteria for including and excluding studies for analysis were set to minimise the possibility of selection bias.
CEP first sought evidence based guidelines on the topic, searching the National Guideline Clearinghouse, MEDLINE and the Cochrane Library. We then searched for systematic reviews and published clinical trials of different catheter maintenance protocols. Multiple databases were searched. A total of 17 searches were run from November 2007-January 2008. They yielded six relevant guidelines and six systematic reviews. The searches for published clinical trials returned a total of 1,145 hits, from which 94 papers were retrieved for review. Twenty-two met criteria for inclusion in our evidence analysis.
Some of the systematic reviews on heparin for catheter flushing combined results from different interventions such as heparin added to total parenteral nutrition, subcutaneous heparin, and heparin flushes. Combining those results for a single conclusion about the effectiveness of heparin is not valid because there is no reason to believe the interventions are equally effective.
We compiled evidence tables (Mitchell, 2009) examining:
- Six studies directly comparing heparin flushing with other interventions;
- Four other heparin flush studies;
- Three studies of continuous heparin infusion;
- Four studies of a heparin bonded catheter;
- Three studies of a urokinase flush;
- Four studies of pressure caps.
In no case was there sufficient data from similar trials to allow meta-analysis of the results. Some studies were not randomised trials, and could have been affected by differences in the patient groups compared. In short, the evidence base on heparin for catheter maintenance is small and of low quality.
The randomised trials found no significant difference in catheter patency rates between flushing with heparin and saline. One non randomised trial found a significant effect favouring heparin flush.
There was no evidence that could help us quantify the risk of HIT from heparin used to maintain catheter patency. Since HIT is uncommon, it would take an extremely large study to measure this risk. We did not find evidence that the other interventions, such as continuous heparin infusion or urokinase flushing, had an effect on catheter patency.
Only one published study compared pressure caps with conventional caps in adults; it was confounded because pressure caps were used only for inpatient care and conventional caps were used for outpatients. Any measured difference in occlusion or infection could have been the result of differences in the patient groups. We broadened our criteria to include paediatric studies. None of the three trials including paediatric patients were randomised, but all reported increased bloodstream infection rates with pressure caps. In one study, the difference was statistically significant. Results of studies measuring the effect of pressure caps on catheter patency were inconsistent.
The evidence for using heparin to flush CVCs is small, and the published studies are of low quality. There was some evidence that pressure caps are associated with increased risk of infection. The CEP stated there was insufficient evidence to conclude that flushing with heparin is more effective than flushing with saline alone. In light of these findings, nursing policy for maintaining CVCs was changed to include flushing catheters with only saline, and we have implemented this over the last 18 months. During this time we have reduced the catheter associated bloodstream infection rate, have not had an increase in catheter or vein occlusion, and have reduced nursing workload without compromising patient safety.
- This is a summary of a paper first published in the Journal of Advanced Nursing (Mitchell et al, 2009)
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