James H. Williams, MD Associate Professor of Anesthesiology Madison Foushee, MD Resident in Anesthesiology Andrey Bortsov, MD Assistant Professor of Anesthesiology Kathleen A. McGraw, MA, MLS Health Science Library University of North Carolina at Chapel Hill Chapel Hill, North Carolina Needleless connectors have distinct advantages, especially eliminating needlestick injuries. But they also have the disadvantage of decreasing flow rates, which is problematic when significant volume resuscitation might be required. In these cases, needleless connectors should be removed. Needleless connectors in IV systems have compelling advantages but can also dramatically decrease flow rates. In cases that might require volume resuscitation, needleless connectors may need to be thoughtfully removed to maintain proper vascular access. A systematic review of the literature and a local quality improvement project have led to our conclusion that the application of a needleless connector constitutes perforce saying goodbye to large-bore IV access. Remove Needleless Connectors From Large–Bore IV Access A key decision for anesthesiologists is what constitutes proper vascular access, taking into account the characteristics of the patient and the proposed procedure. At times, great effort is required to obtain proper vascular access and, especially in the case of central vascular access, this is not without risk to the patient. If volume resuscitation might be required, this takes on even greater importance; understanding the factors that affect IV systems, therefore, can be described as a high-yield topic for anesthesiologists. Our everyday use of IV systems can belie their complexity.1-3 This article is focused on needleless connectors as important components of IV systems. These components are increasingly being used because of their compelling advantages, such as reduced risk for needlestick injuries,4 decreased blood exposure, and heightened convenience. However, a systematic review of the literature revealed that needleless connectors can dramatically affect flow rates, so we performed a local quality improvement project to measure the effect of needleless connectors in combination with the vascular access devices that we use. We confirmed that needleless connectors dramatically decrease the potential flow rates in an in vitro experimental system. Needleless connectors are common, so one interpretation of our data is that with their use, anesthesiologists are necessarily saying goodbye to large-bore IV access. Our interpretation of the literature and our data emphasize that placing large-bore vascular access with a needleless connector is futile, and in cases where significant volume resuscitation is required, needleless connectors should be removed. Needleless Connectors Limit Large-Bore IV Catheter Flow to That of a 20-Gauge IV An experimental system was established to measure the potential maximum flow rates using the vascular access devices that we use institutionally. This type of approach has been used successfully elsewhere in the literature.5-7 A Belmont Rapid Infuser with high-flow tubing was attached to a range of IV catheters and central lines with and without a needleless connector (Figure 1). The system was filled with 0.9% normal saline, the maximum flow rate was selected on the pump, and a series of measurements were made after 30 seconds (to allow for stabilization). We use the term “theoretical maximum flow rates” to describe the results as an acknowledgment that this is an experimental system, which does not take into account other important factors, not the least of which are the characteristics of the patient.3 This approach is easily recreated in your own practice. Among the advantages of this experimental system are that it is easy and it eliminates the inaccuracy of gravity systems. It is also clinically meaningful because this is what we use in cases requiring fluid resuscitation and massive transfusion. Some of the configurations tested were able to run at the maximum rate (750 mL/min) of the Belmont Rapid Infuser, but many were pressure limited (about 300 mm Hg). This system also allowed us to focus on the effects from the CARESITE needleless connector that we used. The results reported here are from this specific needleless connector; however, we believe the findings are typical of needleless connectors generally. The results are plotted as the mean of the measurements ±SEM (error bars are smaller than plot symbols). Hypothesis testing reveals significant differences between the 3 experimental conditions for those catheters signified by an asterisk (analysis of variance with correction for multiple testing). SEM, standard error of the mean All of the IV catheters that we use locally were tested under 3 conditions:
We tested these experimental conditions because this is the IV system most commonly used at our institution. By itself, 6-inch tubing is an important resistive component, but the use of the entire system of catheter, needleless connector, and extension leads to dramatic changes in flow rates. For small-bore IV catheters, the addition of a 6-inch extension and needleless connector has marginal effect. (And yes, we recognize that it is ridiculous to connect the Belmont Rapid Infuser to a 24-gauge IV—except for the purposes of these experimental measurements!) However, IV catheters larger than 20 gauge begin to show significant differences in theoretical maximum flow rates. Our interpretation of this graph is that needleless connectors with a 6-inch extension change large-bore IV access to that of a 20-gauge IV. The result: Say goodbye to large-bore IV access. Placing large-bore IV access with a needleless connector is futile, unless the plan is to remove the connector should volume resuscitation become required. Needleless Connectors Can Limit Flow in Central Lines For central access, 7-Fr central lines with 3 lumens are valuable tools, but for major vascular access are not considered usable. This is shown which demonstrates that the addition of a needleless connector to this central line has effects on flow rate that are unlikely to be clinically significant. Although hypothesis testing reveals significant differences with the addition of needleless connectors in those pairs with an asterisk (t-test), the clinical effects are interpreted to be modest. The theoretical maximum flow rates through a 20-gauge IV catheter In contrast, other central lines are highly affected. The addition of a needleless connector to the side arm of an 8.5-Fr introducer leads to a drastic decrease in theoretical flow rate. Major vascular access via an 8.5-Fr introducer is limited to flow rates comparable to a 20-gauge IV when the needleless connector is added. Further studies were performed with an 8-Fr, 2-lumen catheter, 9-Fr MAC introducer, and a 7-Fr rapid infusion catheter. In all cases, the same basic result was obtained: Flow rates were reduced to approximately that of a 20-gauge IV. Flow through the introducer is similar to a 20-gauge IV with the addition of a needleless connector. Asterisks signify significant pairwise differences (t-test). Literature Review Finds Flow Changes A systematic review of the literature was undertaken to further understand the effects of needleless connectors on flow rates. A search strategy was developed for PubMed with the goal of including all devices, both experimental and clinical data, and all publication types, limiting results to English-language research. The search strategy was adapted for Embase via Elsevier and the American Society of Anesthesiologists (ASA) abstract archive website. All databases were searched on June 9, 2016. Ninety-four items were downloaded and 20 duplicates were removed. After reviewing bibliographies of relevant articles, 7 articles were added. A total of 81 titles and abstracts were assessed by 2 reviewers using tools from www.covidence.org, with 16 papers advancing to full text review by 1 reviewer, 11 of which were analyzed. The PubMed search syntax used for the search query, where tw=title word: (Needleless[tw] OR needle free[tw] OR antireflux valve×[tw] OR reflux valve×[tw] OR closed catheter×[tw] OR clave[tw] OR clearlink[tw] OR interlink[tw] OR Q-syte[tw] OR smartsite[tw] OR CLC2000[tw] OR flolink[tw] OR MaxPlus[tw] OR Posiflow[tw] OR ultrasite[tw] OR Bionector[tw] OR microclave[tw]) AND (intravenous[tw] OR IV[tw] OR CVC[tw] OR central venous[tw]) AND (flow×[tw] OR pressure×[tw]). Filters: English PRISMA, preferred reporting items for systematic reviews and meta-analyses A systematic search of the literature found that needleless connectors decreased flow rates, sometimes dramatically. There is great heterogeneity in the results which reflects differences in device design, different experimental approaches, and different measurement techniques. Some investigators used pressurized systems similar to that used in this study, and others used gravity systems. Some of the gravity systems were modeled after standard conditions for measurement of flow in IV catheters: British standard 4843 or the current International Organization for Standardization ISO standard 10555.8,9 Some investigators measured flow rates using pressurized pumps like our study, but others calculated flow from volume over a period of time. The studies also included both IV catheters and central lines of various types. Consistent results are found with connectors in the setting of hemodialysis and with other components such as antireflux valves.8,10
Differences in fluids are important to note, because the effect of a needleless connector varies with the fluid that is tested. For example, results are not the same for crystalloid and packed red blood cells. In the setting of massive transfusion, packed red blood cells and blood products would be the typical resuscitation fluids, and a decrease in flow rate with needleless connectors would be very clinically significant. Studies that assessed effects of needleless connectors with packed red blood cells included Lehn et al5,11,12 and Saw and Arendts.13 Sharpe et al, in their 2013 ASA abstract, made measurements with a number of connectors.9 Their study is the only one to report needleless connectors thatdo not decrease flow: Tego & 1o2 connectors (both, ICU Medical). With these 2 connectors, there was no statistically significant decrease in crystalloid flow rate. The results reported in Table 1 are culled from the published abstract; further investigation would be of great interest. Based on a systematic search of the literature, it is best to conclude that inclusion of needleless connectors in IV systems will decrease flow. The physics of IV systems is discussed in the next section with the conclusion that calculations based on theory are not currently possible. Each anesthesiologist might find information about the devices in their practice from this table, but ultimately the most reasonable approach would be to make measurements with the devices and configurations that you actually use. IV Systems Are Complex It is not currently possible to make theoretical predictions about flow rates in IV systems for several reasons. Experimental measurements of vascular access devices8,19,20 and IV systems2,3 are found to deviate from those predicted under ideal conditions using the Hagen-Poiseuille equation or Reynolds number. In addition, characteristics of the individual patient are clearly of tremendous importance,3 which is why the results are reported as “theoretical maximum flow rates.” Finally, the number of combinations and permutations in an IV system are very numerous (i.e., endless), with each component potentially exerting a very important effect.2 For example, in Figure 2, the 6-inch connector alone leads to a dramatic decrease in flow rate. For IV catheters, the gauge measurement system itself is nonlinear.21 While this paper focuses on needleless connectors, there are many components that may lead to changes in flow rate: drip chambers, injection ports, stopcocks, changes in tubing size, extensions, and others. Each anesthesiologist can reflect on the many possible combinations and permutations of IV systems that are encountered in their practice. Our everyday use of IV systems tends to disguise their complexity.1-3 Several investigators have proposed that transitional flow, with elements of both laminar and turbulent flow, best accounts for the experimental measurements in vascular access devices and IV systems. Predicted flow rates under the idealized conditions of the Hagen-Poiseuille equation or Reynolds number do not match that measured experimentally and thus are of limited use clinically.20 In a study of venous catheters, Selwyn and Russell20 reported that flow rates were linear with decreases in length, but alsolinear (not to the 4th power) with increasing radius.8 McPherson and co-investigators19 also studied IV catheters and concluded the experimentally determined flow rates were best accounted for by a mixture of both laminar and turbulent flow. For IV systems, Philip and Philip2 found that the experimental data were best fit using a binomial, with coefficients RL and RT, that may relate to actual laminar and turbulent flow conditions; a case for transitional flow was presented in their discussion. It is reasonable to assume that needleless connectors lead to the nonuniformity of the fluid path8 and perhaps increase transitional flow,2 which may account for the dramatic changes in flow rates with these devices. Some of the heterogeneity of results found in the systematic review of the literature (Table 1) might be explained by differences in the design and engineering of these devices. There is a large variety of needleless connectors, and several classification schemes have been proposed.4,22 A reasonable way to categorize needleless connectors was proposed by Hadaway in 20124: Simple connectors are those without internal moving parts such as those with an external split septum, and complex connectors are those with internal moving parts such as a mechanical valve. A further way to categorize these connectors is by fluid displacement, with some needleless connectors described as having neutral, negative, or positive fluid displacement. A positive fluid displacement connector will expel fluid back into the pathway upon disconnection.4,22 The physics of IV systems is complex, and theoretical predictions of flow rates do not match real-world findings. Our systematic review of the literature demonstrates great heterogeneity in the effects of needleless connectors on flow rates. For the individual anesthesiologist, a very practical recommendation would be to simply measure the flow rates of the IV systems in your local practice, especially those that are used in the most demanding applications such as fluid resuscitation and massive transfusion. The approach presented in this paper (Figure 1) is a simple and clinically meaningful way to make these measurements. Needleless Connectors Are Common Because They Have Compelling Advantages Needleless connectors were developed to decrease the risk for needlestick injuries,4,22 and for this reason alone, they should remain an important part of perioperative IV systems. They also have other compelling advantages, but some areas of concern remain. This paper is focused on the effect of these devices on flow rates, especially when combined with large-bore IV access; the recommendation is to be thoughtful with their application and recognize their risks and benefits, but not to remove completely needleless connectors from our practice. Needleless connectors are very ingenious (Figure 6), and if for no other reason than to decrease the risk for needlestick injuries, they are likely to remain a part of perioperative IV systems. Needlestick injuries are an important issue for health care workers, and needleless connectors are reported to be highly effective for risk reduction.4,22 Other advantages of needleless connectors are convenience and decreased blood exposure. Risk reduction and safety devices are mandated by the US Needlestick Safety and Prevention Act, as administered by the US Occupational Health and Safety Administration. Nevertheless, there are several areas of concern with needleless connectors in addition to the changes in flow rates discussed in this paper. Most importantly, some studies have reported increased rates of catheter-related bloodstream infections when needleless connectors are used.4,23 Some investigations have also linked the use of needleless connectors to increased risk for catheter occlusion.4Inadvertent misconnections to needleless connectors can lead to clinically significant and sometimes fatal venous air embolism.24 Conclusion Thoughtful choices about IV systems, including whether to use needleless connectors, can increase patient safety. The authors would be thrilled if you remember the core message of this review, which is that needleless connectors typically constitute saying goodbye to large-bore IV access. Acknowledgments Anesthesiology residents at the University of North Carolina have a 1-month academic medicine rotation (AMR) during their PGY-1 year. This project was conducted as a part of this experience, and the authors recognize the AMR team: Susan Martinelli, MD, Marietta Wagner, Chris Howard, MD, Fei Chen, PhD, David Zvara, MD, and David Mayer, MD. References
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