NC labeling does not appear to correspond with manufacturer claims.
Two of 13 NCs passed the test for bidirectional flow control.
All NCs reflux either on connection or disconnection.
Neutral displacement does not appear to be present in the NCs tested in this observational study.
Accurate bidirectional flow control, reflux cycle, and volume of reflux beyond the manufacturer’s performance claims will assist in the proper use of NCs.
Background: Manufacturers designed needleless connectors (NCs) to reduce needlestick injuries and exposures to bloodborne pathogens. All NCs displace fluid, and most do not control fluid movement through the device. The observed bidirectional fluid movement and reflux may not be consistent with how the manufacturer of the device describes NC. Reflux may lead to a significant patient safety risk as it relates to intraluminal thrombotic occlusion and infection.
Methods: The in vitro observational study 1 (OS1) systematically tested bidirectional flow control; the ability prevented retrograde fluid from flowing into the infusion system. Researchers tested 13 commonly used NCs. The observational study 2 (OS2) measured the amount of displaced fluid in each NC paired grouping during connection and disconnection of a Luer locking device.
Results: OS1: Eleven NCs failed bidirectional flow control, and 2 passed bidirectional flow control. OS2: All 13 NCs had varying amounts of fluid displacement or reflux. The measured volume of reflux for NCs during disconnection was 0.17 μL to 114.65 μL. The measured volume of reflux for NCs during connection was 11.73 μL to 34.43 μL.
Conclusion: NC labeling does not appear to correspond with manufacturer claims. Neutral displacement does not appear to be present in the NCs used in this observational study. To properly instruct health care professionals about using the various NCs available, it is imperative to know the accurate bidirectional control, reflux cycle, and volume of reflux beyond the manufacturer’s performance claims. Precise information may assist the clinician in reducing intraluminal blood exposure of vascular access devices.
For 25 years, needleless connectors (NCs) have been developed as a solution to the Occupational Safety and Health Administration directive to prevent needlestick injuries and exposures to bloodborne pathogens.1 As a result, many types and designs of NCs emerged. Categories have been created for marketing purposes such as negative, positive, neutral, and antireflux to categorize each NC.2,3 The question remains how much reflux is acceptable for NCs labeled for each category. The labels do not always seem to match the NC performance (Table 1) nor the current definitions (Table 2), yet no agency or governing body has created quantitative guidelines to categorize or classify NCs.2,4 Favorable traits identified in NCs are those that have no blood reflux and have no clamping sequence.5–8 The optimal design of a NC remains unclear and unresolved.9,10
The labeling of NCs confuses many clinicians,3 leading to difficulty in the use and management of the device. Inconsistent language creates part of the confusion for health care professionals seeking to understand the function and management of these devices.4 Studies show that 47%–79% of nurses do not know the type of NCs they are using or the appropriate clamping sequence for the device. Understanding the appropriate connect-disconnect-clamping sequence is essential to using the device effectively.2,6
The observational studies conducted were to answer the research question: Do needleless connector manufacturer claims on bidirectional flow and reflux equate to in vitro quantification of fluid movement?
The observational study 1 (OS1) was to determine if the NC had bidirectional flow control. A NC with bidirectional flow control will allow fluid to flow by gravity. Once the simulated venous pressure rises higher than the pressure inside the infusion container, a diaphragm will close and stop the fluid from flowing back into the vascular access device. Bidirectional flow control prevents retrograde flow of fluid when the simulated venous pressure is higher than infusion pressure.
The observational study 2 (OS2) measured the fluid displacement of each NC during 2 phases, connection and disconnection. Displacement into the device is considered reflux, and displacement away from the device is considered infusion or positive displacement (Table 3).
A minimal comprehension of fluid dynamics is essential to understand flow control and blood reflux. Principles of fluid dynamics include fluid movement, fluid displacement, and viscosity when considering how blood enters the catheter lumen. Fluid movement is when gravitational kinetic energy (hanging intravenous fluids) transforms into kinetic energy, and the fluid flows through tubing.11 Pressure changes influence fluid movement and flow from high to low.3–5 An external source such as a syringe, an infusion pump, or a male Luer connection and disconnection creates mechanical pressure. Coughing, vomiting, exertion, mechanical ventilation, and heart contraction create physiological or internal pressure.3,5
Fluid displacement occurs when an object pushes into the fluid and moves the fluid of equal volume.12 As an object moves from the fluid, the fluid resends and creates a vacuum. Negative displacement or blood reflux and positive fluid displacement occur when an object (male Luer) pushes into an elastomeric centerpiece or septum, and the fluid moves an equal volume,12,13 essentially, when internal parts of the NC move in and out of the fluid pathway and blood can reflux into the catheter lumen. The reflux exposes the intraluminal wall of the catheter to blood.
Methods and Materials
Upon institutional review board approval via Integreview (SMG-1001), testing was conducted by a registered nurse (RN) and a mechanical engineer (BS). Researchers selected 13 commercially available NCs. In vitro OS1 (Figure 1) observed the ability of 13 NCs to provide bidirectional flow control and overcome the associated pressure changes which occur in a closed intravenous (IV) system. All 13 commercially available NCs were purchased in manufacturer-supplied boxes from medical distributors.
In vitro OS2 (Figure 2) used a manometer to observe and measure the reflux and positive displacement of the 13 NCs. Researchers tested each NC 3 times for a total of 390 tests to determine the average amount of fluid movement, which occurs after the connection and disconnection of a 10 mL syringe. The fluid used in both experiments was the glycerol-water (GW) solution (44% glycerin, 56% water by weight), a commonly used blood-mimicking solution with a density of 1124.1 kg/m.14 However, the fluid used has the same viscosity of blood, but the studies focused on the movement of the fluid, not the fluid interaction with the walls of the IV system related to the viscosity.
The 13 NCs used in both OS1 and OS2 are Baxter Clear-link®, Baxter One-Link®, BD MaxPlus®, BD MaxZero®, BD Smartsite®, B Braun Caresite®, B Braun Ultrasite®, ICU Medical Clave®, ICU Medical Microclave®, ICU Medical Neutron®, Nexus Medical NIS-5®, Nexus TKO-6P®, and Rymed Invision Plus®.
Observational Study 1
Using a VATA Adult Venipuncture Training Arm, the researcher placed a peripheral intravenous catheter (PIVC) in a simulate vein. The researcher connected a 1,000 mL (infusion side) and 100 mL (patient side) collapsible IV bag filled with 100 mL of the GW solution to the specific needleless connector attached to the PIVC site. The 1,000 mL bag’s initial position started on an IV pole 182.88 cm (72 inches), 101.6 cm (40 inches) above the infusion site. The clamp was released and the bag lowered slowly to 5.08 cm (2 inches) below the simulated insertion site.
The tinted fluid enabled the observation of the retrograde fluid movement. Ten of each of the 13 NCs were tested, totaling 130 tests. When retrograde flow occurred, the connector failed the bidirectional flow control test. The NC passed the bidirectional flow control test if there was 0 retrograde flow.
Observational Study 2
Ten NCs of each of the 13 types were tested 3 times for fluid displacement during connection and disconnection (Figure 2). A manometer used 2 graduated glass tubes. The large and small glass tube diameter measured 1.13 mm and 0.634 mm, respectively, and needed to measure the range of displacement. Before each test, the system was purged of air and calibrated the meniscus at 6 cm of water column or 15 cm for NCs with large negative displacement.
With the system calibrated, the testing began with the connection of the syringe to the NC. After documenting the results, the researcher recalibrated and purged the system of air. Next, the researcher disconnected the syringe and recorded the results. The testing was repeated 3 times on each NC, totaling 390 tests.
The researcher tested each NC for the ability to control retrograde flow or bidirectional flow. In OS1, 2 of the 13 NCs passed (Table 4) the bidirectional flow control test. All other NCs failed.
In OS2, the researcher measured fluid displacement during the connection and disconnection of a Luer locking device. In Figure 3, the NCs are ranked by most reflux to least. The right side of the table illustrates the amount of fluid movement that occurs during disconnection and the left during connection. The red bars indicate the average amount of reflux that occurred, and the corresponding blue bars indicate the average amount of positive displacement.
During OS1, all NC fluid flows by gravity without difficulty. Two NCs stopped the flow and did not allow retrograde flow as the bag lowered to 5.08 cm (2 inches) below the simulated insertion site. The ICU Medical Neutron and the Nexus Medical TKO-6P passed the test for bidirectional flow control. When tubing is attached, the NC is an open conduit for fluid or blood to move freely either in or out of the patient bidirectionally. Limiting retrograde blood flow may reduce the incidence of thrombotic occlusion and biofilm formation.
OS2 showed a wide range of reflux. Other published studies found similar results3,5 (Table 1). In Figure 3, 2 distinct groups emerge, those with reflux during connection and those with re-flux during disconnection. Figure 3 shows the amount of reflux (red bars) and positive displacement (blue bars), the phase that reflux occurred, connection or disconnection, and ranks the NCs in order of most reflux to least reflux. A reference point of 10 μL is labeled to identify the amount needed to fill a 22 ga. 1″ PIVC. A subdivision among the NCs refluxing less than 10 μL is 2 connectors that refluxed less than 0.2 μL. Both connectors have a dome-shaped silicone diaphragm designed to prevent reflux and are labeled antireflux.
The instructions of use (IFUs) and 2 documents2,3 are sources of labeling in the published literature. Only 6 of 18 published NCs have labels in the IFU. When reviewing all 3 documents, the neutral NCs had a range of reflux of 2.93 μL to 10.80 μL. The definition in the Infusion Therapy Standards of Practice (ITSOP; Table 2) for a neutral NC is, “Neutral NC—Contains an internal mechanism designed to prevent blood reflux into the catheter lumen upon connection or disconnection.”10(pX) According to this study, all NCs labeled neutral did reflux and had no bidirectional flow control. Looking closely at the definition from the ITSOP of neutral NC, the quantitative measurement found in this study does not support this definition.3–6,15,16 Health care providers may create accidental reflux during disconnection when clamping is not performed for NCs labeled as neutral that might lead to a significant patient safety risk as it relates to intraluminal thrombotic occlusion and infection.17,18
NCs that reflux on the connection have been labeled as positive displacement connectors. The benefit of these NCs is that, upon disconnection, a small burst of saline displaces forward, helping to clear blood in the catheter. However, when considering the volume of reflux of 11.73 μL to 34.43 μL on connection, there is considerable intraluminal blood exposure for these NCs. One positive displacement NC is labeled “Zero reflux, Neutral reflux, anti-reflux,” yet had published reflux of 6.90 μL to 18.84 μL and said explicitly, “Eliminates the need for specific clamping sequences or techniques.” Two of the 3 positive NCs report no clamping sequence, and 1 recommends clamping after disconnection to the Luer. This type of NC could benefit from the clamp being engaged before access to minimize the exposure time of the reflux.
Two of the NCs labeled antireflux perform similarly. The range of reflux was 0.17 μL to 0.18 μL. The difference appears to be the dome-shaped silicone diaphragm within the needleless connector. This category of NC contains an internal mechanism designed to prevent blood reflux into the catheter lumen both upon connection and disconnection, which is precisely the definition of neutral NCs. The positive displacement of the 2 connectors ranged from 0.18 μL to 1.06 μL. The fluid displacement, positive or negative, was the smallest in the connectors labeled antiflux.
One limitation of this study is the simulation in vitro of bidirectional flow and reflux. Unlike actual patients, in vitro study restricts many variables in patient vasculature and blood composition.
A second limitation is catheter material. Some materials may have different abilities to repel binding protein from the blood. Further studies are needed on the interaction of blood with variation in materials used for the manufacture of vascular access devices.
NC labeling does not appear to correspond with manufacturer claims. Neutral displacement does not appear to be an accurate label for any NCs. The definition of neutral NCs more appropriately describes the function of the antireflux NC. Appropriate labeling of the NCs is either reflux on connection (positive displacement) or reflux on disconnection (negative displacement), with the notable feature of antireflux to control bidirectional flow. To properly instruct health care professionals about the use of the various NCs available, it is imperative to have accurate information on bidirectional flow control, reflux cycle, and volume of reflux beyond manufacturer’s performance claims. Precise information may assist the clinician in reducing intraluminal blood exposure of vascular access devices.
S.M.G.: Chief Executive Officer of Vascular Access Consulting, Consultant Researcher Beaumont Hospital, Royal Oak Michigan, Speaker’s Bureau for Ethicon, Consultant for Inter-rad Medical, Consultant for B Braun, Consultant for Nexus Medical.