- © 2020 American Society of Radiologic Technologists
Comparison of 2 CT Contrast Media Injection Systems: Visual Air Identification and Injector Face Cleaning
- Adam Czibur, MS,
- Mikayla Ferchaw, BS,
- David Vazquez, BS, R.T.(R)(CT),
- Shannon Mikell, R.T.(R)(CT),
- Carsten Schwenke, PhD and
- Jan Endrikat, MD, PhD
Abstract
Purpose To compare the MEDRAD Stellant and MEDRAD Stellant FLEX computed tomography contrast media injection systems in terms of radiologic technologists’ ability to visually identify air in the syringes at various distances and under different lighting conditions, as well as the ease of cleaning contrast media spills on the injector faces.
Methods Ten experienced radiologic technologists performed 104 tests (52 per injector) in normal light and in ambient light conditions. The tests were randomized for the radiologic technologists’ distance from the injector at 2 ft (61 cm), 8 ft (244 cm), and 16 ft (488 cm). In addition, the authors tested the cleaning efficiency of the Stellant injector face with raised buttons and the Stellant FLEX injector face with buttons on a flush surface by applying a mixture of contrast media and invisible ultraviolet ink. Radiologic technologists followed 2 cleaning protocols: a quick clean (5 seconds) and a full clean (1 minute). Residual contrast mixture was measured.
Results The Stellant FLEX injector had an overall higher rate of correct air identification than did the Stellant injector, 97.5% vs 86.9%, respectively (P < .001), with improvement seen at greater distances. The rates for the Stellant FLEX injector remained stable for all distances (99.4%-93.9%; P < .003). A similar result was seen with ambient lighting: The visibility of air in the Stellant FLEX injector remained stable (P < .001). During cleaning, the Stellant FLEX injector required less time to reach a greater level of cleanliness and showed less contrast mixture residue, especially after the quick clean procedure (16% and 59%, respectively; P < .001).
Discussion Injector manufacturers provide various technologies to assist radiologic technologists in visualizing the presence of air in a syringe. The Stellant injector features clear syringes with FluiDots as an air identification technology. The Stellant FLEX injector incorporates an added feature called Beacon technology. This study’s results are highly clinically relevant because unintentional iatrogenic air injection occurs in clinical practice and can, in rare cases, severely harm patients.
Conclusion Radiologic technologists showed an improved ability to identify air in the syringes in the Stellant FLEX system. In addition, radiologic technologists were confident about their identification, specifically at greater distances and in ambient lighting conditions. The Stellant FLEX injector face also enabled quicker and more efficient cleaning.
Accidental administration of air into a patient’s vein or artery can occur during various clinical interventions, including contrast-enhanced computed tomography (CT) procedures in which contrast media is injected intravenously.1–3 Air injected into the venous system can become trapped in the lung capillaries and usually is absorbed with no clinical symptoms.4,5 Although the lethal dose of air is unknown, case reports suggest that 100 mL to 300 mL of air injected into the venous system of adults can be fatal.6 In patients with a patent foramen ovale (prevalence 20-27%), air bubbles very rarely travel into the arterial systemic circulation, causing stroke or myocardial infarction.1,4,7,8 Medical workers must be vigilant because they are the primary preventive measure for avoiding the introduction of air into a patient’s vein or artery. Technologies that help medical workers identify air in the syringe are beneficial.
Most marketed CT injectors provide effective features and instructions to support radiologic technologists in avoiding air injections. Established measures include transparent syringes that allow visualization of air and careful, sometimes automated, filling processes for the syringes in upright injector head orientation. Two peristaltic CT injectors, CT motion (Ulrich Medical) and CT Exprès (Bracco), provide air detectors along the fluid path. Although such detectors provide an additional air identification option during the injection process, they do not enable identification of air in the fluid path before the injection. This can interrupt synchronized CT procedures, potentially exposing patients to unnecessary contrast media and radiation doses.
The MEDRAD Stellant and Stellant FLEX syringes and tubing (Bayer) are made of transparent plastic polyethylene terephthalate, which allows air to be visible without additional aids when standing close to the injector in normal and ambient lighting conditions. FluiDots—an air identification technology developed by Bayer—were introduced to further assist radiologic technologists in identifying air, especially in empty syringes. FluiDots are small regions embedded in the transparent syringe material that appear as narrow ellipsoids when the syringe is empty or contains air and almost round when the syringe contains fluid (see Figure 1). However, at greater distances from the injector and in ambient lighting, gross air in the syringes is difficult to see. Stellant FLEX syringes are equipped with an additional feature referred to as Beacon technology. With this technology, the presence of fluid in an upright syringe is indicated by the reflection of the orange plunger at the syringe tip (see Figure 1).
Visual air detection technologies (FluiDots and Beacon). FluiDots change from ellipsoids in an empty syringe to round dots in a fully filled syringe. The Beacon technology indicates the presence of fluid in an upright syringe by reflecting the plunger color at the syringe’s tip. Image courtesy of the authors.
In addition, radiologic technologists often have limited time to clean the injector system between patients because of increasing numbers of patients and additional administrative duties. Contrast media injection systems are used in fast-paced radiology environments in which hygiene and time efficiency are essential.9,10
When contrast media spills on the injector interface, the residual contrast is a sticky, viscous mixture that can harden and build up, potentially damaging the system. The Stellant FLEX injector face has flush buttons to facilitate efficient cleaning.
The purpose of this study was to investigate whether an additional method of air identification, namely the Beacon technology that indicates the presence of fluid in an upright syringe, would result in an additional means of air identification compared with transparent syringes with FluiDots alone. To the best of the authors’ knowledge, the effectiveness of various visual air identification technologies and the cleanability of injector faces have not been investigated.
Methods
Ten radiologic technologists (8 women, 2 men) with various years of experience (4-23 years) in CT were recruited from the Pittsburgh, Pennsylvania area. Inclusion criteria for the study participants included certification in radiologic technology with CT experience and experience using a Stellant injector. In addition, 2 Bayer field service technicians (both men) participated in the injector face cleaning protocol. Participants’ demographic data and years of experience are shown in Table 1.
Participant Demographics
Air Identification Experiment
Four syringes labeled A through D were filled with various volumes of air and f luids for the assessments (Table 2). Each of the 10 radiologic technologists performed a total of 104 assessments (52 assessments per injector). Of these 52 assessments per injector, 26 assessments were conducted in normal light (124.86 lux) and 26 in ambient light (43.59 lux). The 26 assessments were performed in 2 runs, in which each run tested 13 combinations of 2 syringes each (see Figure 2).
Syringe Air and Fluid Volumes
Experimental setup for air detection per participant. Image courtesy of the authors.
The pairs of 2 syringes mounted on the injector at the contrast side and saline side were selected from a choice of 4 differently filled syringes (A-D). The frequency of syringes shown was statistically determined by the assumed difficulty in recognizing air. For example, at greater distances, air identification mainly relies on identification of the fluid level in the syringe. Therefore, the completely empty syringe (A) and the syringe filled with 15 mL of air (C), in which the fluid line sits at the base of the cone of the syringe, were predicted to be difficult for participants to identify air.
The sequence of syringe combinations for each injector was the same for all 26 syringe combinations for each participant. The distances for determining air—2 ft (61 cm), 8 ft (244 cm), and 16 ft (488 cm)— were randomized over the 26 syringe combinations for each participant. The distances were chosen to approximate the distance between the radiologic technologist and the injector head when standing near the injector (2 ft [61 cm]), midway between the control room and the injector head (8 ft [244 cm]), and inside the control room behind glass (16 ft [488 cm]).
Procedure
All radiologic technologists were familiar with using the FluiDots as part of their prior experience and daily use of their site’s Stellant injector. Radiologic technologists were trained to use the Beacon technology before starting the study.
The 26 syringe combinations per injector were assessed at randomized distances between the radio-logic technologist and syringe (2 ft [61 cm], 8ft [244 cm], and 16 ft [488 cm]). The moderator of the study asked the radiologic technologist to go to a predefined location and stand with his or her back turned to the injector. Then, the moderator installed the syringes and waited approximately 5 seconds until any fluid was visibly settled in the syringe before asking the radiologic technologist to turn around to face the injector. The radiologic technologist then was asked to respond in 1 of 3 ways: “Yes, air is in the syringe,” “No, no air is in the syringe,” or “I’m not sure whether there is air in syringe.” All responses were recorded by the moderator.
Statistics
The endpoint of this study was measuring the increased effectiveness of air detection using the Beacon technology. The sample size was calculated for each syringe volume to identify differences between the injectors at a distance of 8 ft (244 cm). Assuming differences in rates of correct air identification of 30% to 70% at the various volumes, sample sizes as shown in Table 2 were needed to show statistically significant differences at a 2-sided level of significance of 5% with 80% power. Half of the measurements were done in each light condition (ie, ambient vs normal). Correlations between the percentage of missed air identification and radiologic technologist sex, height, and years of experience were assessed using the Spearman correlation coefficient.
To investigate the influence of injector type, distance, and lighting condition, logistic models based on generalized estimation equations were used to account for the readers’ multiple assessments. With syringes A, B and C, the radiologic technologist’s answer was counted as a success if he or she said “Yes, air in syringe.” With syringe D, the radiologic technologist’s answer was counted as a success if he or she said “No, no air in syringe.” All other answers were counted as incorrect. In addition to the main factors, the interaction effects between distance and light condition, respectively, were included in the model and subjected to a backward selection to identify factors and interactions relevant for the outcome variable.
To assess confidence in air identification, answers “yes” and “no” were set to “certain” and “not sure” was set to “uncertain.” The proportions of uncertain assessments were compared between the injectors using the generalized estimation equations as described above.
Calculations were performed using SAS Version 9.4 (SAS Institute Inc) and plots were assembled using R version 3.3.3 (R Core Team).
Injector Face Cleaning Experiment
The Stellant injector face consists of raised buttons with an inset edge between the injector face and front cover; the Stellant FLEX injector face features enclosed buttons that sit flush on the injector face and front cover. The metal and plastic components of 3 Stellant and Stellant FLEX injector faces were coated with a mixture of 25 mL Bayer Ultravist 370 contrast media and 4 mL fluorescent ink (UVStuff Invisible UV Ink, cyan), applied with 10 full sprays. This sticky, viscous mixture was applied homogeneously to each injector face using a rubber baster. The contrast mixture dried for at least 1 hour before the start of the cleaning procedures.
Procedure
Ten radiologic technologists and 2 field service technicians performed 2 cleaning procedures developed for this study: quick clean and full clean. The cleaning procedures were conducted linearly (ie, one immediately following the other) for each injector: first quick clean, then full clean, with the aim of mimicking a typical cleaning procedure for a nonbiological injector spill (eg, with contrast media). Additional steps would be required if biological contamination occurred (eg, with blood).
In the quick clean procedure, the radiologic technologists were provided with a Sani-Cloth Plus (PDI Healthcare) wipe and asked to remove as much contrast mixture as possible in a 5-second timeframe for each injector face.
In the full-clean procedure, the radiologic technologists were provided with a dampened, lint-free cloth and warm water and asked to perform a 1-minute intensive cleaning of each injector face, followed by another 5-second quick clean using a Sani-Cloth Plus wipe. The moderator kept track of the time for each cleaning scenario.
The amount of remaining contrast mixture on the injector faces was analyzed using a Cannon PowerShot SX20IS digital camera. All images were taken using a standardized setup with respect to the camera, injector head position, and black light position. Illumination with black light made the residual mixture of contrast media and ultraviolet ink light up. Four images were taken per injector state (see Figure 3):
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■ before the contrast mixture application, to ensure sufficient contrast mixture removal between participants (not part of data)
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■ after the contrast mixture application (baseline)
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■ after the quick clean
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■ after the full clean
Cleaning protocol: Injector faces of Stellant featuring buttons with crevices (A) and Stellant FLEX with buttons on a flush surface (B). The blue frame indicates the area technologists usually interact with. Stellant (C) and Stellant FLEX (D) injectors shown in black-light after full cleaning, with residual contrast with ink visible. Images courtesy of the authors.
Postprocessing software (NIH ImageJ version: 1.51j8) was used to extract the areas of residual contrast mixture on the injector face. Thresholding was applied consistently across all injector faces and used to optimize identification and quantification of the contrast mixture.
Data points were logged on a spreadsheet, and the percentages were scaled according to the equation: to make all injector images proportional across the data.
Statistics
The percentage of residual contrast mixture was analyzed using a mixed model with the factors of injector, cleaning (quick clean, full clean), and injector × cleaning interaction. The radiologic technologist was modeled as a repeated factor. Least square means of percentages of contrast mixture left on the injector face were computed, along with 95% confidence intervals, which were truncated at 0% and 100%. Calculations were performed using SAS Version 9.4.
Radiologic Technologists’ Preferences
At the end of all study procedures, the radiologic technologists were asked which injector they preferred for the air identification and injector face cleaning portions of the study. The preferences for one or the other injector were assessed using a sign test.
Air Identification Experiment Results
Effect of Radiologic Technologists
The radiologic technologists’ number of years of experience showed no relevant or significant correlation with correct air identification (Spearman correlation coefficient = −0.09, P = .49). Sex and height also did not significantly affect the results (correlation coefficients for sex = −0.06 [P = .64] and for height = 0.01 [P = .92]).
Distance and Lighting
Although both injectors provided equally strong results when radiologic technologists stood directly at the injector (96.1% for the Stellant injector vs 99.4% for Stellant FLEX injector), the overall rate of correct air identification improved for the Stellant FLEX injector and declined for the Stellant injector with increasing distances from the injector, 97.5% vs, 86.9%, respectively (P < .001) (see Figure 4A).
Correct air detection with Stellant vs Stellant FLEX injectors. A. overall. B. By distance. C. By lighting. D. By distance and lighting (*indicates statistical significance for the test on differences between the injectors). Graphs courtesy of the authors.
The rates for correct air identification for the Stellant FLEX injector remained stable across all distances (99.4% to 93.9%). The Stellant injector showed a high rate of correct air identification at the injector; however, the rate decreased as distances increased (96.1% to 75.6%). The percentage of correct air identification was also strong for the Stellant FLEX injector at 8 and 16 ft (244 and 488 cm) (P < .003) (see Figure 4B) and with the shift to more ambient lighting (see Figure 4C).
Considering the 2 parameters of distance and lighting in combination, correct air identification rates decreased with distance and ambient lighting for the Stellant injector, from 96% at 2 ft (61 cm) to 73% at 16 ft (488 cm), whereas Stellant FLEX injector rates remained more stable, ranging from 96% to 100% (see Figure 4D).
Confidence in Air Identification
Participants’ certainty regarding their air identification improved with the Stellant FLEX injector compared with the Stellant injector. For the Stellant FLEX injector, in only 2 of 520 assessments (0.4%) were the participants uncertain of their conclusion (P = .05).
Injector Face Cleaning Experiment Results
After the quick clean, the Stellant FLEX injector face had less contrast mixture remaining than did the Stellant injector face (16% and 59% residual contrast mixture, respectively). After the full clean, these figures dropped to 2.3% and 5.2% (P < .001), respectively (see Figure 5). The average time needed for cleaning the Stellant FLEX injector face to the radiologic technologist’s satisfaction and according to the procedures defined in this study was 28 seconds, compared with 46 seconds for the Stellant injector face.
Cleaning protocol: Residual contrast mixture on the injector face. Graph courtesy of the authors (*indicates statistical significance for the test on differences between the injectors).
Participant Preference Results
Overall, 9 of 10 participants preferred the Stellant FLEX injector for identifying air in ambient lighting (P = .022), whereas 8 of 10 participants preferred the Stellant FLEX injector in normal lighting (P = .11). All 12 participants preferred the Stellant FLEX injector for injector face cleaning (P < .001).
Discussion
Air Identification Experiment
The results of this study provide evidence that the addition of the Beacon technology allows for more reliable air identification, particularly at greater distances from the injector and in the ambient lighting conditions of a CT suite.
These results are highly clinically relevant because unintentional iatrogenic air injection occurs in clinical practice and can, in rare cases, severely harm patients.7
Fatal cases have been reported in the context of injection of larger amounts of air with CT contrast media.11,12
This topic is an important and potentially under-appreciated complication of medical procedures,13 considering venous air embolism after intravenous administration of contrast media has been reported to occur in 11% to 23% of patients.14–18 Radiologic technologists must be properly trained to check for air before starting an injection.
Today, technologies in areas other than CT, are aiming to filter air from infusion lines. For example, Xu et al recently published a comparison of 2 air removal systems for vascular access lines. In their study, they added air at 5 mL/min to 15 mL/min to saline flows of 250 mL/min to 750 mL/min and measured air bubbles >10 μL downstream. They concluded that the new vascular access line air removal device (VALARD) was highly efficient.19 Also, Zoremba et al investigated the air elimination capabilities of 3 infusion devices by applying a fluid at a flow of 100 mL/min to 800 mL/min mixed with 25 mL/min to 200 mL/min air in a bench study. All of the tested devices eliminated air to such a degree that the negligible remaining air volume would not cause significant air embolism.20 Finally, Wilkens et al reviewed the topic of accidental intravenous infusion of air. They quoted the International Electrotechnical Commission guidelines for infusion pumps, which permit up to 1 mL of air in 15 minutes and discount bubbles smaller than 50 μL.7
Although the above-mentioned systems eliminated air from patient lines in infusion systems, they are neither used nor validated in the context of CT contrast media injections. In the high-pressure CT injector environment, in-line filters constitute significant fluid path obstacles, potentially leading to excessive injection pressures and the inability to inject required higher flow rates.
Injector Face Cleaning Experiment
This current study showed that the radiologic technologists more efficiently cleaned the contrast mixture from the Stellant FLEX injector face than from the Stellant injector face. Significant contrast mixture was removed from the Stellant FLEX injector face in the quick-clean and full-clean cleaning protocols in this study. After the full clean, small amounts of contrast mixture (2.3%) remained on the Stellant FLEX injector face. The Stellant injector face could be cleaned sufficiently, but not as quickly or efficiently as the Stellant FLEX injector face because of the differences in the injector faces’ button design.
Although research on removing bioburden from medical instruments is evolving, and some standards exist for reusable medical devices, to the best of the authors’ knowledge soiling of the injector with sticky contrast media agents—a common problem in radiology suites—has not been investigated. This study did not test the biological efficacy of the cleaning process or investigate the effectiveness of a new cleaner. Instead, the study investigated the relative cleanability of the 2 injector faces.
Limitations
For the air identification portion of the study, the following limitations need to be addressed:
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■ The plungers of all 4 syringes were set at the bottom, independent of their filling status. This is not the case in the routine setting for the syringes that are not completely filled with contrast media or saline (A, B, and C).
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■ Lighting differs among CT suites. The selected luminance levels for normal and ambient lighting might not be representative for all CT suites.
For the injector face cleaning protocol, the experimental scenario with high amounts of soiling with the contrast mixture and the 1-hour long drying period might not be realistic but were chosen to demonstrate the issue. In addition, not all radiologic technologists use Sani-Cloth Plus to clean contrast media spills, and the biological efficacy of this cleaning method was not tested.
Conclusion
The Stellant injector allowed reliable air identification at the injector; however, the Stellant FLEX injector when used properly, provides an additional benefit of reliable visual air identification at greater distances, regardless of the lighting conditions. In addition, the Stellant FLEX injector face was more efficiently cleanable than was the Stellant injector face.
Acknowledgements
The authors thank the radiologic technologists and field service technicians who participated in this study.
Footnotes
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Adam Czibur, MS, and Mikayla Ferchaw, BS, are human factors engineers for Bayer in Indianola, Pennsylvania.
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David Vazquez, BS, R.T.(R)(CT), is a computed tomography scan supervisor for the Medical University of South Carolina Radiology in Charleston.
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Shannon Mikell, R.T.(R)(CT), is a radiography and computed tomography quality technologist for the Medical University of South Carolina Radiology in Charleston.
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Carsten Schwenke, PhD, is a statistician in Berlin, Germany.
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Jan Endrikat, MD, PhD, works in Radiology Research and Development for Bayer AG in Berlin, Germany, and for the Department of Gynecology, Obstetrics and Reproductive Medicine at the University Medical School of Saarland in Homburg/Saar, Germany.
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Conflict of interest: some authors are employees of Bayer AG, which funded this research.
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Reprint requests may be mailed to the American Society of Radiologic Technologists, Publications Department, 15000 Central Ave SE, Albuquerque, NM 87123-3909, or emailed to publications{at}asrt.org.
- Received October 23, 2018.
- Accepted July 18, 2019.
