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Q What is the standard regarding isotonic sodium chloride solution versus heparin in pressure monitoring systems?

A Barbara Leeper, RN, MN, CCRN, replies:

Traditionally, heparin has been added to isotonic sodium chloride solution or 5% dextrose in water for use in maintaining patency of pressure monitoring catheters including arterial, pulmonary artery, and central venous pressure catheters. The use of heparin for intermittent flushes to maintain patency of peripheral catheters was discontinued by most clinicians several years ago. However, the practice has continued for maintaining patency of pressure monitoring catheters until recent years. Clinicians identified an opportunity to cut costs by using nonheparinized solutions for maintaining patency of these catheters; in addition, there is a real concern regarding the risk for the development of heparin-induced thrombocytopenia (HIT).

The evidence supporting the use of nonheparinized flush solutions is mixed. Most studies have been conducted on peripheral intravenous catheters and arterial pressure monitoring systems. A limited number of studies have examined the use of nonheparinzed flush solution in pulmonary artery catheters; most have investigated central catheters.

The benefit of heparin in peripheral and arterial catheters was studied before the American Association of Critical-Care Nurses (AACN) Thunder I Project. Clifton et al (1) compared the patency of isotonic sodium chloride solution and heparin solutions for maintenance of arterial catheter patency in 1991. They conducted a double-blind randomized study in 30 adult medical intensive care unit patients. The concentration of the heparin flush solution was 4 U/mL in 0.9% sodium chloride. Data demonstrated that the use of a heparin flush solution resulted in a catheter survival rate of 86% at 96 hours compared with a rate of 52% after 40 hours in those with an isotonic sodium chloride only solution. The researchers concluded that the use of isotonic sodium chloride flush solution for radial artery catheters was associated with an increased frequency of occlusion and did not support the use of nonheparinizedflush solutions. (1) However, another controlled study with a similar sample size, investigated patency rates in patients with intermittent infusion devices and found no difference in the patency rates with the use of isotonic sodium chloride solution versus heparin flush solution. (2)

In 1993, AACN (3) published the results of a large scale randomized clinical trial (Thunder I Project) evaluating the effects of heparinized and nonheparinzed flush solutions on the patency of arterial pressure monitoring catheters. A total of 5139 patients from 198 hospital critical care units in the United States, Canada, and Australia composed the sample. Patients were randomly assigned to heparinized and nonheparinzed flush solution treatment groups. Data were collected at 4-hour intervals for up to 72 hours on the presence of an acceptable square waveform and arterial backflow. The results indicated that heparin did significantly affect the patency of arterial catheters over time. Catheters were kept patent without heparin also. However, the use of a heparin flush did not guarantee patency of the catheter. Variables affecting probability of patency of the catheter included the use of anticoagulant therapy, catheter length (less than 2 inches vs longer than 2 inches), arterial catheter site (femoral vs other), and gender. The investigators concluded that clinicians need to make decisions about the risks of HIT compared to risks associated with nonpatency of the arterial catheter. When long-term patency is critical, decisions may be different from those made when short-term use is contemplated. (3,4)

Randolph and coworkers (5) conducted a systematic review and meta-analysis of 26 randomized controlled trials evaluating the effect of heparin (intermittent use or continuous infusion) on duration of catheter patency and prevention of complications associated with its use in peripheral venous and arterial catheters. Two of the 13 were peripheral arterial catheters and the rest were peripheral venous catheters. Infusion of low-dose heparin was found to significantly prolong the patency of radial artery catheters and reduce the risk of clot formation. (5) A second meta-analysis of randomized controlled trials was conducted by the same group of researchers for the purpose of examining the benefit of heparin in central venous and pulmonary artery catheters, specifically addressing thrombus formation and infection. (6) The meta-analysis included 14 randomized controlled trials. They found that heparin effectively reduces thrombus formation and may reduce catheter-related infections in patients with central venous and pulmonary artery catheters. The investigators did not include any studies comparing the use of a nonheparinized solution with a heparinized solution.

HIT occurs infrequently, but can be life-threatening. Cardiac surgery patients have been identified to be at the greatest risk for developing HIT related to the use of heparin while on cardiopulmonary bypass during the surgical procedure. The overall frequency is approximately 2%.7 Of interest is that 27% to 50% of cardiac surgical patients will form HIT antibodies. Of those, fewer than 10% will actually develop thrombocytopenia even with the continuation of heparin infusions during the postoperative period. Patients with the strongest antibody test results have been identified as those who are most likely to develop HIT. (7)

Many clinicians have changed their practice to the use of nonheparinzed flush solutions for pressure monitoring systems. There are anecdotal reports of freedom from adverse events, such as radial artery thrombosis, and catheter patency rates that are similar to those when heparin flush solutions were used. There are reports on quality improvement projects related to this issue, but extremely limited randomized clinical trials leaving this topic ripe for further research.

So, where does this leave us? Based on case reports of patients developing HIT, patient exposure to heparin should be limited where possible. (8) If the decision is made to change practice from the use of heparin flush solutions to nonheparin flush solution for the purpose of maintaining patency of pressure monitoring catheters, an effort should be made to track outcomes including catheter patency rates, vessel thrombosis, and incidence of HIT.

Editor's Note: The following "Ask the Expert" feature by Barbara Leeper, RN, MN, CCRN, addresses a topic that has generated numerous questions from our readers. The article is reprinted from Critical Care Nurse, April 2006:137-38. Please note that the recommendations apply to adult patients.

References

(1.) Clifton GD, Branson P, Kelly HJ, et al. Comparison of normal saline and heparin solutions for maintenance of radial artery catheter patency. Heart Lung. 1991;20:316.

(2.) Ashton J, Gibson V, Summers S. Effects of heparin versus saline solution on intermittent infusion device irrigation. Heart Lung. 1990;19:608-612.

(3.) American Association of Critical-Care Nurses. Evaluation of the effects of heparinized and nonheparinized flush solutions on the patency of arterial pressure monitoring lines: the AACN Thunder Project. Am J Crit Care. 1993;2:3-15.

(4.) AACN's Thunder Project Task Force. Arterial catheter complications and management problems: observations from AACN's Thunder Project. Crit Care Nurs Clin North Am. 1993;5:557-562.

(5.) Randolph AG, Cook DJ, Gonzales CA, Andrew M. Benefit of heparin in peripheral venous and arterial catheters: systematic review and meta-analysis of randomized controlled trials. Br Med J. 1998;316:969-975.

(6.) Randolf AG, Cook DJ, Gonzales CA, Calle A, Andrew M. Benefit of heparin in central venous and pulmonary artery catheters: a meta-analysis of randomized controlled trials. Chest. 1998;113:165-171.

(7.) Warkentin TE, Greinacher A. Heparin-induced thrombocytopenia and cardiac surgery. Ann Thorac Surg. 2003;76:2121-2131.

(8.) Ling E, Warkentin TE. Intraoperative heparin flushes and subsequent acute heparin-induced thrombocytopenia. Anesthesiology. 1998;89:1567-1569.

Barbara Leeper is a clinical nurse specialist in Cardiovascular Services at Baylor University Medical Center, Dallas, Texas.

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