Statistical analysis included paired StudentÃs t-test with 95% confidence intervals (95% ... An active US education pro
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Short-axis versus Long-axis Approaches for Teaching Ultrasound-guided Vascular Access on a New Inanimate Model Michael Blaivas, MD, RDMS, Larry Brannam, MD, RDMS, Eleanor Fernandez, MD Abstract Objectives: To determine whether a short-axis (SA) or longaxis (LA) ultrasound (US) approach to guidance for line placement results in faster vascular access for novice US users. Also, to assess if there was a difference in the number of skin penetrations and needle redirections between the two guidance techniques. Methods: This was a prospective, randomized, observational study of emergency medicine (EM) residents at a Level I trauma center. A gelatin dessert and dietary fiber supplement mixture, providing a realistic US image, were placed inside a synthetic arm skin that is used for training phlebotomists and contains a rubber vein filled with red fluid at a depth of 1.5 cm. After a 30-minute tutorial on US-guided vascular access, EM residents were randomized to one of two groups. Group one attempted SA first and then the LA. Group two tried LA first followed by the SA. Time from skin break to vein cannulation, number of skin breaks and needle redirections, and difficulty of access on a 10-point Likert scale as reported by residents were recorded.
Statistical analysis included paired StudentÕs t-test with 95% confidence intervals (95% CIs). Results: Seventeen EM residents participated. The mean times to vein cannulation in SA and LA were 2.36 minutes (95% CI ¼ 1.15 to 3.58) and 5.02 minutes (95% CI ¼ 2.90 to 7.13), respectively (p ¼ 0.03). The mean numbers of skin breaks for SA and LA were 4.18 (95% CI ¼ 1.18 to 7.17) and 5.76 (95% CI ¼ 1.83 to 9.69), respectively (p ¼ 0.49). The mean numbers of needle redirections in the SA and LA were 13.71 (95% CI ¼ 4.51 to 22.89) and 18.17 (95% CI ¼ 7.95 to 28.40), respectively (p ¼ 0.51). The mean difficulty scores for SA and LAwere 3.99 (95% CI ¼ 2.42 to 5.67) and 5.86 (95% CI ¼ 4.32 to 7.40), respectively (p ¼ 0.17). Conclusions: Novice US users obtain vascular access faster with an SA approach on an inanimate model. Key words: emergency ultrasonography; ultrasound education; ultrasound assisted line placement; vascular model; emergency medicine; educational ultrasound model. ACADEMIC EMERGENCY MEDICINE 2003; 10:1307–1311.
Obtaining vascular access in patients presenting to the emergency department is one of the fundamental skills of emergency medicine (EM). Many patients requiring vascular access lack easily accessible peripheral venous sites. Factors including body habitus, vascular disease, and injection drug use may render peripheral sites difficult or even impossible to locate by the usual landmark and palpation method. Multiple studies have evaluated the use of ultrasound (US) guidance for central venous access in the emergency department, but very few studies address the use of US guidance for peripheral access.1–3 In addition, US guidance for brachial and basilic vein cannulation in emergency department patients has been evaluated, but the technique required two people, and different vein access techniques were not compared.4
Studies designed to evaluate the differences between US-guided versus landmark-guided techniques for central venous access have preferentially used a short-axis (SA) technique as the preferred approach for cannulation.1,5,6 Whereas the long-axis (LA) approach to vessel access also has been used successfully, we could find no studies designed to evaluate the differences in the two techniques. Previous studies have evaluated venous access through use of the distal femoral vein using US guidance, but, again, the SA approach was employed.7 Despite the fact that two very different techniques exist for vessel visualization, one approach appears to predominate in US-guided central venous access. The SA approach attempts to view the vessel in crosssection while venous access is obtained (Figure 1B). In contrast, the LA approach employs a technique that views the length of the vessel during cannulation (Figure 1A). It may be assumed that a preference toward the SA approach exists in previous studies, but there are no data to support the use of this technique exclusively based on ease of use, rate of success, and time to gain vascular access. We performed a prospective, randomized, observational study on EM residents at a Level I trauma center to determine which approach results in faster
From the Department of Emergency Medicine, Medical College of Georgia, Augusta, GA. Received March 28, 2003; revision received June 23, 2003; accepted June 30, 2003. Address for correspondence and reprints: Michael Blaivas, MD, RDMS, Department of Emergency Medicine, Medical College of Georgia, 1120 15th Street, AF-2056, Augusta, GA 30912-4007. E-mail:
[email protected]. doi:10.1197/S1069-6563(03)00534-7
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Figure 1. (A) Needle shown entering the synthetic vessel in the long axis (arrows). (B) Needle is shown entering the vessel in the short axis (arrows).
vascular access by the novice US user. Secondarily, we attempted to determine whether one approach resulted in fewer penetrations of the model skin and needle redirections.
METHODS Study Design. This was a prospective, randomized, observational study of the SA vs. LA US-guided approach for venous cannulation by novice US users. The study was IRB reviewed and approved. Study Setting and Population. The study was conducted at a Level I trauma center with an EM residency program. An active US education program exists in the department, and hospital-based credentialing for emergency ultrasonography is in place. US use in the ED includes a variety of traditional and novel applications both for clinical practice and research. No previous US-guided vascular access educational program had been used for the residents. First-, second-, and third-year EM residents were enrolled in the project. None of the residents were US-credentialed, and only one had successfully placed a vascular line under US guidance before this project. Study Protocol. Residents were given a 30-minute didactic session on US-guided vascular access that included related basic physics, previous published literature, machine operation, image fine tuning, typical approaches to a vessel, and step-by-step instructions from placing a probe on the simulated arm to obtaining vascular access. The presentation used graphic representations, anatomy drawings, still US images, video clips of subjects performing USguided needle insertion, and real-time video from an US machine screen during insertion. Residents were not given hands-on practice or demonstrations on the model arm or other simulator before the project. A gelatin dessert and dietary fiber supplement mixture were used to provide a realistic soft tissue
echo texture substance similar to the texture of the human arm. This mixture was suggested by representatives of Sonosite (Bothell, WA) and is used in their simulations. The mixture was formed into a cylindrical shape that fit inside synthetic arm skin used for training phlebotomists (Figure 2A). The skin was tested by the authors and found to have excellent US transmission qualities. The vein used to simulate an actual human vein also was taken from the commercially available phlebotomist training arm. The vein was placed at approximately 1.5 cm in depth in the arm to simulate a deeper peripheral vein or, potentially, a central vein. It once again was imaged by the authors to assure realism and that the synthetic vein could adequately simulate a typical real vein on penetration with a needle (Figure 3A and 3B). An intravenous fluid bag filled with nontoxic, red-colored liquid was used to run fluid through the vein (Figure 2B). Participants would be able to place the needle into the vein and withdraw red-colored fluid that simulated blood. Residents were randomly assigned to one of two groups. Group one attempted cannulation of the ‘‘vein’’ using the SA first and then the LA. Group two attempted the LA first and then the SA (Figures 1A and 1B). Any resident not wishing to participate was excused. Residents were not allowed to observe others attempting cannulation before trying it themselves. Measures. Investigators recorded time from the EM resident placing the US probe and needle on the inanimate model to the time that simulated blood was drawn into the syringe. The number of total times the needle broke the skin and the number of times the residents drew back to realign the needle was recorded. The residents were asked to grade the difficulty of the SA and the LA approach on a 10-point Likert scale. The US machine used was a Sonosite, Ilook 25. Data Analysis. Sample size calculation revealed that to have 80% power with 5% alpha, we would need
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Figure 2. (A) The venous access model is show with a resident placing the probe in the short axis over the synthetic vein. (B) Close up showing source of simulated blood.
approximately 15 subjects to detect a 50% difference for time to vascular access between the SA and LA approaches. A 50% difference in the time taken to achieve vascular access is likely to be clinically significant. Statistical analysis included a paired StudentÕs t-test with 95% confidence intervals (CI). Data were analyzed using statistical calculators from a commercially available software package, Stats Direct (Cheshire, United Kingdom).
RESULTS A total of 17 EM residents were enrolled in the study. No resident declined to participate in the research project or asked that his or her data not be used in analysis. The mean time to vein cannulation in SA was 2.36 minutes (95% CI ¼ 1.15 to 3.58). The mean time to vein cannulation in LA was 5.02 minutes (95% CI ¼ 2.90 to 7.13). The 112% difference of 2.65 minutes (95% CI ¼ 0.24 to 5.07) was statistically significant (p ¼ 0.03).
The mean number of skin breaks for SA was 4.18 (95% CI ¼ 1.18 to 7.17). The mean number of skin breaks for LA was 5.76 (95% CI ¼ 1.83 to 9.69). The difference of 1.59 (95% CI ¼ 3.22 to 6.40) was not statistically significant (p ¼ 0.49). The mean number of needle redirections in the SA was 13.71 (95% CI ¼ 4.51 to 22.89). The mean number of needle redirections in the LA was 18.17 (95% CI ¼ 7.95 to 28.40). The difference of 4.47 (95% CI ¼ 9.69 to 18.64) was not statistically significant (p ¼ 0.51). The mean difficulty score for SA as recorded on the Likert scale was 3.99 (95% CI ¼ 2.42 to 5.67). The mean difficulty score for LA was 5.86 (95% CI ¼ 4.32 to 7.40). The difference of 1.86 (95% CI ¼ 0.86 to 4.58) was not significant (p ¼ 0.17). No resident failed to obtain simulated blood from the vascular access model in either the LA or SA approaches. Procedure order did not affect outcome variables. Comparison of residents who were selected to attempt vascular access in the SA first versus those attempting LA first showed no statistical difference
Figure 3. (A and B) Synthetic vein is shown in the long axis and short axis, respectively. Shadowing is not typically seen distal to a real vein as in (A).
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for time to cannulation (p ¼ 0.42). There was no difference detected for these two groups for the secondary measures of number of needle redirections and skin penetration (p ¼ 0.51 and 0.39, respectively).
DISCUSSION The AHRQ has recently advised that US guidance be used for the placement of central lines to decrease morbidity and mortality associated with the procedure.8 Line placement is a common procedure for EM physicians both in training and in practice. Patients presenting to the emergency department frequently have poor vascular access due to a multitude of etiologies such as chronic illness, hypovolemia, intravenous drug abuse, vasculopathy, and others. Such patients also are likely to fail attempts at peripheral access and may therefore require central line access. Although intravenous access is a fundamental skill of EM, it may be challenging to even the most seasoned emergency physician in such difficult patients. Central access is more likely to be chosen over deeper peripheral veins that cannot be palpated and are not subject to the same relatively reliable landmark rules that may be applicable to internal jugular, subclavian, and femoral lines. However, if deeper peripheral intravenous access sites could be obtained, the dangers associated with central line placement may be avoided. Blind attempts at central access can lead to a variety of complications such as hematoma, pneumothorax, arterial puncture, hemothorax, chylothorax, brachial plexus injury, air embolus, catheter malposition, catheter knotting, dysrhythmia, and arterio-venous fistula.9–12 Several attempts may be required to gain venous access in some of the most critically ill patients. Repeated attempts may occur at one location or involve several different sites. When venous access cannot be attained rapidly, lifesaving measures may be delayed. Traditionally, all these attempts would be made using anatomical landmarks and palpation. The first description of US use for central line placement appeared in the literature in 1984 and involved the utilization of Doppler only, without grayscale imaging, to identify the location of the central vein before placing the catheter.13 Since this first description, a number of specialties have utilized either direct US guidance or US marking of a vessel’s path to guide placement of central lines. Specialties utilizing this technology have included anesthesiology, surgery, EM, and radiology.14 Emergency physicians first described the use of US in the assistance of central line placement in the early 1990s. Since then, several articles and abstracts have appeared relating to central and peripheral venous access under US guidance1,2,4,15; the utility of US in both peripheral and central venous access can hardly be argued. However, little investigation regarding teaching mod-
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els or the easiest vessel approach for novice emergency sonographers has been reported. In essence, there are two basic approaches to a vessel: the SA and LA. In the short axis, on US, the vessel appears to be a dark circle (Figure 3B). In the LA approach, the vessel appears as a dark, thick line (Figure 3A). The thickness of the line or size of the circle depends on vessel diameter. There are theoretical advantages to each approach. For instance, in the LA, the entire length of the needle can potentially be tracked on the US screen as it enters the blood vessel (Figure 1A). However, this requires more hand-eye coordination than the SA approach. In the SA approach, the vessel is easy to see and the operator must perform less alignment. The disadvantage is that the entire length of the needle will not be seen, rather only a portion of it as it passes through the US beam under the transducer. Because US education is now a part of the emergency residency curriculum, it would be of great help to know which approach is easier to teach and perform. Our data showed that EM residents new to US guidance for vascular access obtained access much faster using the SA approach. They tended to rate the SA approach as easier, but this difference was not statistically significant. Surprisingly, the number of skin penetrations with the needle and number of needle withdraws and redirections also showed no significant difference. Emergency US programs instituting US-guided line placement may consider teaching both the SA and LA approach to residents and letting individuals decide which approach they prefer. Similarly, if efficiency is of the essence, SA may be taught first because it appears to yield fastest access. Our model was primarily intended to simulate peripheral line access. To date, much has been written about US assistance for central line placement both in emergency US literature and other specialties.1,3,5,16,17 However, focus recently has shifted to peripheral access under US guidance.4,18,19 Peripheral veins that particularly lend themselves to US-guided line placement include the basilic, cephalic, and saphenous veins. Unfortunately, these veins may not be readily palpable and thus may be difficult to access blindly. Conversely, they are often large enough to allow for rapid resuscitation, and when long catheters are inserted, they can be quite durable, such as in the case of pic lines.20 Keyes et al. utilized US-guided peripheral line placement in 101 ED patients, the majority of whom were intravenous drug users or were significantly obese.4 The investigators had a success rate of 91%, with the majority of successful placements (73%) requiring only one attempt under US. The patients studied are those who often would receive a central line with all of its potential complications, such as deep venous thrombosis, significant hemorrhage, and pneumothorax.21 It is important to note that the technique used for peripheral line placement differs little from
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that used for central lines. Furthermore, because peripheral vessels are much smaller that the large femoral or internal jugular veins, such a model is good practice for either. The model itself was relatively simple, requiring easily obtainable ingredients from a grocery store. The true cost came from the phlebotomy training kit we purchased, which was then modified by removing the foam layer and replacing it with the gelatin-and-fiber mixture. The entire cost was just under $70 dollars. The model was stored in a refrigerator and was able to be used repeatedly for training. After approximately 60 days, the model arm’s substrate became more and more dehydrated, leading to increased echogenicity of the ‘‘soft tissue’’ surrounding the synthetic vein, thus limiting its long-term storage ability. However, the model was able to tolerate well over 100 cannulations.
LIMITATIONS This was a study on an inanimate model, and such models can never duplicate humans exactly. However, the arm model used is one employed for teaching intravenous access to phlebotomists and has been refined over several years. The US characteristics of human tissue were well simulated by the mixture of gelatin dessert and dietary fiber supplement, giving it a realistic appearance, and is the same combination used by a prominent US manufacturer for their training. The preferred method of access by novice sonographers may change over time, as experience increases; this model would not capture this. Longitudinal studies of resident US-guided intravenous line placement are needed to determine which approach is of most utility over time.
CONCLUSIONS Novice US users obtain vascular access faster using an SA approach than an LA approach on an inanimate arm model. There was no statistically significant difference in the number of skin penetrations with a needle or number of needle withdrawals between the two techniques. Ease of use as rated by the residents did not show statistical significant difference. References 1. Miller AH, Roth BA, Mills TJ, Woody JR, Longmoor CE, Foster B. Ultrasound guidance versus the landmark technique for the placement of central venous catheters in the emergency department. Acad Emerg Med. 2002; 9:800–5. 2. Hudson PA, Rose JS. Real-time guided internal jugular vein catheterization in the emergency department. Am J Emerg Med. 1997; 15:79–82.
1311 3. Hrics P, Wilber S, Blanda MP, Gallo U. Ultrasound-assisted internal jugular vein catheterization in the ED. Am J Emerg Med. 1998; 16:401–3. 4. Keyes LE, Frazee BW, Snoey ER, Simon BC, Christy D. Ultrasound-guided brachial and basilic vein cannulation in emergency department patients with difficult intravenous access. Ann Emerg Med. 1999; 34:711–4. 5. Farrell J, Gellens M. Ultrasound-guided cannulation versus the landmark-guided technique for acute haemodialysis access. Nephrol Dialysis Transplant. 1997; 12:1234–7. 6. Kwon TH, Kim YL, Cho DK. Ultrasound-guided cannulation of the femoral vein for acute haemodialysis access. Nephrol Dialysis Transplant. 1997; 12:1009–12. 7. Sato S, Ueno E, Toyooka H. Central venous access via the distal femoral vein using ultrasound guidance. Anesthesiology. 1998; 88:838–9. 8. Evidence Report/Technology Assessment Number 43: Making health care safer: a critical analysis of patient safety practices. Rockville, MD: US Dept of Health and Human Services, Agency for Healthcare Research and Quality; 2001. AHRQ publication 01-E058. 9. Bernard RW, Stahl WM, Chase RM Jr. Subclavian vein catheterizations: a prospective study. II. Infectious complications. Ann Surg. 1971; 173:191–200. 10. Mansfield PF, Hohn DC, Fornage BD, Gregurich MA, Ota DM. Complications and failures of subclavian-vein catheterization. N Engl J Med. 1994; 331:1735–8. 11. Sznajder JI, Zveibil FR, Bitterman H, Weiner P, Bursztein S. Central vein catheterization. Failure and complication rates by three percutaneous approaches. Arch Intern Med. 1986; 146:259–61. 12. Steele R, Irvin CB. Central line mechanical complication rate in EM patients. Acad Emerg Med. 2001; 8:204–7. 13. Legler D, Nugent M. Doppler localization of the internal jugular vein facilitates central venous cannulation. Anesthesiology. 1984; 60:481–2. 14. Keenan SP. Use of US to place central lines. J Crit Care. 2002; 17:126–37. 15. Hilty WM, Hudson PA, Levitt MA, Hall JB. Real-time ultrasound-guided femoral vein catheterization during cardiopulmonary resuscitation. Ann Emerg Med. 1997; 29:331–6. 16. Gualtieri E, Deppe SA, Sipperly ME, Thompson DR. Subclavian venous catheterization: greater success rate for less experienced operators using US guidance. Crit Care Med. 1995; 23:692–7. 17. Denys BG, Uretsky BF, Reddy PS. Ultrasound-assisted cannulation of the internal jugular vein. A prospective comparison to the external landmark-guided technique. Circulation. 1993; 87:1557–62. 18. Costantino TG, Fojtik JP. Success rate of peripheral IV catheter insertion by emergency physicians using ultrasound guidance [abstract]. Acad Emerg Med. 2003; 10:487. 19. Blaivas M, Brannam L, Fernandez F. Short Axis versus long axis approaches for teaching ultrasound guided vascular access [abstract]. Acad Emerg Med. 2003; 10:572–3. 20. Barber JM, Booth DM, King JA, Chakraverty S. A nurse led peripherally inserted central catheter line insertion service is effective with radiological support. Clin Radiol. 2002; 57: 352–4. 21. Mian NZ, Bayly R, Schreck DM, Besserman EB, Richmand D. Incidence of deep venous thrombosis associated with femoral venous catheterization. Acad Emerg Med. 1997; 4:1118–21.
