Presented at the Society of Academic Emergency Medicine annual meeting, Washington, DC, May 2008.
Risk Factors for Acute Adverse Events During Ultrasound-guided Central Venous Cannulation in the Emergency Department
Article first published online: 12 OCT 2010
© 2010 by the Society for Academic Emergency Medicine
Academic Emergency Medicine
Volume 17, Issue 10, pages 1055–1061, October 2010
How to Cite
Theodoro, D., Krauss, M., Kollef, M. and Evanoff, B. (2010), Risk Factors for Acute Adverse Events During Ultrasound-guided Central Venous Cannulation in the Emergency Department. Academic Emergency Medicine, 17: 1055–1061. doi: 10.1111/j.1553-2712.2010.00886.x
This study was supported by the Washington University School of Medicine CTSA Grant (UL1 RR024992) and Washington University School of Medicine’s Clinical Research Training Center (KL2 RR024994).
Dr. Theodoro is a paid consultant for Electrocore.
Supervising Editor: Alan Jones, MD.
- Issue published online: 12 OCT 2010
- Article first published online: 12 OCT 2010
- Received December 16, 2009; revisions received February 14 and February 23, 2010; accepted February 24, 2010.
- central venous;
- emergency medicine
Background: Ultrasound (US) greatly facilitates cannulation of the internal jugular vein. Despite the ability to visualize the needle and anatomy, adverse events still occur. The authors hypothesized that the technique has limitations among certain patients and clinical scenarios.
Objectives: The purpose of this study was to identify characteristics of adverse events surrounding US-guided central venous cannulation (CVC).
Methods: The authors assembled a prospective observational cohort of emergency department (ED) patients undergoing consecutive internal jugular CVC with US. The primary outcome of interest was a composite of acute mechanical adverse events including hematoma, arterial cannulation, pneumothorax, and unsuccessful placement. Physicians performing the CVC recorded anatomical site, reason for insertion, and acute complications. The patients with catheters were followed until the catheters were removed based on radiographic evidence or hospital nursing records. ED charts and pharmacy records contributed variables of interest. A self-reported online survey provided physician experience information. Logistic regression was used to calculate the odds of an adverse outcome.
Results: Physicians attempted 289 CVCs on 282 patients. An adverse outcome occurred in 57 attempts (19.7%, 95% confidence interval [CI] = 15.5 to 24.7), the most common being 31 unsuccessful placements (11%, 95% CI = 7.7 to 14.8). Patients with a history of end-stage renal disease (odds ratio [OR] = 3.54, 95% CI = 1.59 to 7.89), and central lines placed by operators with intermediate experience (OR = 2.26, 95% CI = 1.19 to 4.32), were most likely to encounter adverse events. Previously cited predictors such as body mass index (BMI), coagulopathy, and pulmonary hyperinflation were not significant in our final model.
Conclusions: Acute adverse events occurred in approximately one-fifth of US-guided internal jugular central line attempts. The study identified both patient (history of end-stage renal disease) and physician (intermediate experience level) factors that are associated with acute adverse events.
ACADEMIC EMERGENCY MEDICINE 2010; 17:1055–1061 © 2010 by the Society for Academic Emergency Medicine
Prior to the use of ultrasound (US) technology, several observational studies conducted in settings outside of the emergency department (ED) reported that acute adverse events occur in 6.3% to 11.8% of all central line placement attempts.1,2 A single study based solely on ED attempts reported rates as low as 3.4%.3 US guidance reportedly decreases adverse events associated with the procedure. In several settings, US assistance decreased by half the mean number of attempts required to cannulate the vessel and resulted in significant time reduction of the procedure.4–8 Two randomized controlled trials in the ED also corroborate the benefit of US guidance, reporting success rates as high as 98%, as well as a 10% absolute decrease of acute mechanical adverse events.9,10 In addition to guiding operators, US can reveal anatomic variations, thrombi, and damaged vessels.11,12 However, despite these successes, the procedure still fails in some patients.9,10,13 Body mass index (BMI), operator experience, coagulopathy, and history of prior cannulation have been implicated as factors that might increase the chances of an acute adverse event during vascular access without US guidance.14–16 The goal of this study was to better identify patient and operator characteristics that might predispose patients to acute mechanical adverse events from central venous cannulations (CVCs) when using US.
This was a prospective observational study of consecutive central line attempts using US guidance to cannulate the internal jugular vein in the ED. The Human Research Protection Office approved the study. Waiver of consent was granted.
Study Setting and Population
The study was conducted between March 2007 and March 2008 at an academic, tertiary care referral, Level I trauma center with a volume of 84,000 visits per year. The 4-year residency program in emergency medicine consists of 48 residents (12 per class) and 51 faculty. At the time of this study, emergency medicine US directors taught all residents and faculty two 1-hour courses on US-guided central line techniques in lecture format. The lectures consisted of video demonstrating internal jugular vein location, positioning the transducer and US unit, and common pitfalls for cannulation including anatomical variations and thrombosis. No simulation sessions were offered. Physicians further developed their skills in the “apprenticeship model,” meaning that they gained experience while managing and caring for patients who required CVC in the presence of those familiar with the procedure. During this time period, several attending physicians used US guidance, but there was no formal evaluation process of their skill.
Enrolled subjects included a consecutive sample of patients who required US-guided CVC as determined by the team of emergency physicians treating the patient. Patients with concurrent central venous access of the ipsilateral side, evidence of trauma to the neck or thoracic vessels, or any overlying dermal condition that posed a possible contraindication to the procedure were excluded.
In conjunction with the Division of Emergency Medicine’s information technology section, we created a standardized electronic procedure note template. The procedure note was created for the purposes of recording outcomes of CVC attempts. Required form fields included the indication for insertion, the site, whether or not the operator used US guidance, and any acute mechanical event that may have occurred during the procedure. Patients requiring venous cannulation due to lack of peripheral access were defined as “poor access.” Patients who required cannulation for active resuscitation due to shock or hemodynamic monitoring due to sepsis were defined as “septic/hypovolemic or hypotensive.” An attempt at cannulation during cardiopulmonary arrest secondary to trauma or cardiac arrest was defined as a “code line.” For the purposes of this study, we did not record how many needle passes were required for successful cannulation, since our data suggested significant variability in reporting.
We defined US guidance as an attempt during which real-time US assisted the operator in guiding the needle toward the targeted vessel. Attempts that only used US to “mark” or “identify” the vessel, but not actively guide the needle (the static technique), were not included in the study.
We defined an “attempt” as a single operator’s performance of the entire procedure from beginning to end (adequate aspiration and flush of all catheter ports) at a single anatomic site. Any needle passes by another operator, whether at the original site or at another site, were considered a separate attempt. We collected demographic and physical characteristics of the patients from the ED chart or hospital record. If no information regarding the patient’s height and weight were available, we collected this information from the patient’s driver’s license or other identification card. The internationalized normalized ratio (INR) was obtained from the ED record. Hypotension in the ED was defined as a systolic blood pressure ≤ 90 mm Hg. In addition, we captured the administration of vasopressors or inotropes as a surrogate measure for persistent hypotension despite resuscitation. Pharmacy records were cross-referenced with the visit date and patient name. Any patient who was administered epinephrine, norepinephrine, dopamine, or dobutamine was identified as requiring pressors and being “persistently hypotensive.” After primary collection of the data related to the procedure, we retrospectively reviewed hospital charts on those who underwent ED cannulation for any history of renal disease requiring hemodialysis.
Emergency medicine faculty and residents inserted all central lines. Physician experience was defined by postgraduate year (PGY) and self-reported cannulation experience. PGY-4 residents were grouped with members of the EM faculty because they could function as attending physicians in other settings. Operators completed a survey during the study in which they documented the number of central lines they had placed during their careers and how many of their last 10 non-emergent central lines were inserted by US.
The primary outcome of interest was a composite of acute mechanical adverse events attributed to central venous access. From review of the literature and consensus among our group, we defined an adverse event as a cannulation attempt that resulted in a common complication or failure in completing the intended procedure.16–21 Arterial puncture, pneumothorax, hematoma, extravascular or misplacement, and unsuccessful cannulation were all defined as acute adverse events. An arterial puncture was deemed to have occurred if the operator aspirated pulsatile arterial (bright red) blood into an 18-gauge locator syringe. We diagnosed pneumothorax/hemothorax by using plain radiographic films of the chest (either standard posterior-anterior or portable) as read by a radiologist blinded to the technique used for central line cannulation. A pneumothorax/hemothorax identified within 24 hours of line placement was considered an adverse event unless the patient underwent another procedure prior to the CVC that could also cause a pneumothorax on the side in question. Operators or nurses involved in the procedure identified a hematoma if an area greater than 3 cm of bruising or swelling was noted around the insertion. Extravascular placement or misplacement was defined by failure to aspirate blood through any of the ports or a visible extravasation of intravenous fluid in the soft tissues as determined by the physician or nurse involved in the patient’s care. Unsuccessful cannulation was specifically defined as failure to complete the intended procedure by the primary operator for lack of successfully cannulating the intended vessel and aspirating through a port. Any alleged puncture of the vein that resulted in the inability to pass a guide wire was considered unsuccessful.
In cases where more than one adverse event occurred, we recorded the complication that required a therapeutic intervention as the primary adverse outcome. Pneumothorax/hemothorax, unsuccessful cannulation, and misplacement were considered primary adverse outcomes if they occurred simultaneously with arterial puncture and hematoma. Any occurrence of any complication was considered an “adverse event.”
To obtain data on delayed adverse events related to an ED central line, we followed the central lines placed in ED patients until evidence from either hospital records or radiologic records indicated that the ED central line was removed or replaced. These data were obtained retrospectively by three methods: review of cases involving CVC adverse events reported to the ED physician responsible for all quality improvement issues in the Division, retrospective chart review of all nursing charts, and retrospective review of patient discharge summaries.
Discharge summaries were reviewed for any mention of “central line complication” or “cannulation device complication” or “iatrogenic” complication. Mention of any of these terms triggered an audit of inpatient nursing and operative records for the mention of adverse events related to an ED central line. Operative records were reviewed for any mention of a vascular procedure related to central line complications.
Results were entered into an Excel (Microsoft Corp., Redmond, WA) file and later transferred into an SAS (Version 9.2, SAS Institute, Cary, NC) database. Normally distributed continuous variables are presented with means and standard deviations (SDs) and nonnormally distributed variables are presented as medians with interquartile ranges (IQRs). To test associations with having an adverse event, the chi-square test or Fisher’s exact test was used as appropriate for categorical variables. The t-test was used for normally distributed variables, and the Wilcoxon-Mann-Whitney test was used for nonnormally distributed variables.
All variables in this analysis were decided upon a priori based on findings in previous studies and by consensus among the group. Any variable on bivariate testing with a p-value < 0.20 was eligible for the final model. We used this cutoff to allow sufficient opportunity to include patient and physician factors that might influence other variables included in the final model.
Since no explicit classification of “experience” exists, we defined operator experience based on similarly published studies that relied on the number of central line cannulations that physicians placed throughout their career.9,10 We created three levels of operator skill by grouping operators into three experience categories: those who, over the course of their career, had placed fewer than 20 central lines, those who had placed 20–50 central lines, and those who had placed more than 50 central lines. We also categorized the likelihood of operators to place catheters using US guidance. Those who placed eight of their last 10 central lines using US were compared to those who used US less often.
To identify variables independently associated with an adverse event, we performed multivariable logistic regression. The model was built in forward stepwise fashion and variables with a p-value > 0.05 were removed. In our final logistic model, missing physician data for US experience level (5%) were imputed and analyzed. Our results were similar, so we present the final model without the imputed variables. We tested for interactions between variables in the final model. We used the Hosmer-Lemeshow goodness-of-fit test as a diagnostic measure of our final model. To examine predictive accuracy, we created a receiver operator characteristic curve by plotting the predicted probabilities of our model against the dependent variable and generated an area-under-the-curve statistic.
The cohort consisted of 289 CVC attempts on 282 patients who underwent internal jugular cannulation under US guidance. Physicians indicated they placed 203 (70%) central lines for hypovolemia or sepsis resuscitation, 74 (26%) for lack of obtaining peripheral access, and 12 (4%) during active cardiopulmonary resuscitation (CPR). The median age of patients undergoing cannulation was 60 years (IQR = 49–75 years), and the median BMI was 27.02 (IQR = 22.63–32.27). A total of 187 patients exhibited one episode of hypotension (65%, 95% CI = 59.0% to 70.0%) and 102 patients required vasopressors for persistent hypotension (36%, 95% CI = 30.0% to 50.0%). During our retrospective chart review for patients with a history of end-stage renal disease and history of dialysis, double data entry was performed. The kappa for determining a history of dialysis was 0.82 (95% CI = 0.70 to 0.93). Our review identified 33 attempts on patients with a history of end-stage renal disease (11%, 95% CI = 8.3% to 16.0%).
A total of 77 physicians participated in the study. Attending physicians and PGY-4 residents performed 93 attempts (32%), PGY-3 residents performed 71 attempts (26%), PGY-2 residents performed 49 attempts (17%), and PGY-1 residents performed 76 attempts (25%). Physicians with fewer than 20 CVC insertions in their careers attempted 34 cannulations (12%, 95% CI = 8.5% to 16.0%), those with 20–50 career cannulations contributed 80 attempts (29%, 95% CI = 22.8% to 33.1%), and those with more than 50 career cannulations contributed 163 attempts (59%, 95% CI = 50.6% to 62.0%). Information on operator experience was missing in 12 of the 289 attempts (4%). Among these, seven attempts (58%, 95% CI = 32.0% to 80.7%) were performed by physicians in their first PGY year, and five (42%, 95% CI = 19.3% to 68.1%) were by physicians with four or more years experience.
There were 57 adverse events, resulting in an adverse event rate of 19.7% (95% CI = 15.5% to 24.7%). There were 31 attempts resulting in cannulation failure (11%, 95% CI = 7.7% to 14.8%), 20 hematomas (6.9%, 95% CI = 4.5% to 10.5%), and six inadvertent arterial punctures (2%, 95% CI = 1.0% to 4.5%). Patients with end-stage renal disease were more likely to sustain an adverse event (Table 1). Fewer adverse events were noted among patients who required a vasopressor or inotrope infusion for sustained hypotension while in the ED. There were 96 (33%, 95% CI = 28.0% to 38.8%) obese patients (BMI ≥ 30), and 43 (15%, 95% CI = 11.2% to 19.4%) anticoagulated patients (INR ≥ 2), but they sustained no significant difference in adverse events. No pneumothoraces or inadvertent placements in the soft tissues occurred. During follow-up, a single patient treated with heparin was noted to develop a small hematoma. However, no intervention took place, the central line continued to be used, and heparin was not stopped. Other than this single hematoma, no late adverse events were found on follow-up. Fifty-two patients expired (18.4%, 95% CI = 14.4% to 23.4%); however, there was no difference in mortality among those who experienced an adverse event and those who did not.
|Characteristics||Adverse Event (n = 57)||No Adverse Event (n = 232)||p-value*|
|Age (yr), mean (±SD)||62.3 (±17.3)||61.3 (±17.8)||0.685†|
|Female||26 (45.6)||127 (54.7)||0.216|
|African American||33 (57.9)||135 (58.2)||0.968|
|BMI,‡ median (IQR)||27.1 (22.6–31.8)||27.0 (22.6–32.5)||0.924§|
|Obese‡ (BMI ≥ 30)||18 (31.6)||78 (33.6)||0.641|
|COPD or asthma||5 (8.8)||35 (15.2)||0.285|
|History of end-stage renal disease||13 (22.8)||20 (8.62)||0.003|
|Hypotensive in the ED||34 (59.7)||153 (66.0)||0.373|
|Persistent hypotension in the ED||13 (22.8)||89 (38.4)||0.028|
|Concurrent CPR||5 (8.8)||7 (3.0)||0.065|||
|INR,¶ median (IQR)||1.3 (1.1–1.7)||1.3 (1.2–1.7)||0.599§|
|INR ≥ 2||8 (14.0)||35 (15.1)||0.837|
|Hospital mortality||8 (14.0)||44 (19.0)||0.385|
There was an association between volume of procedures and adverse event on bivariate testing (Table 2). There was no statistically significant effect of operator experience according to postgraduate year education or those with a high propensity to use US.
|Adverse Events (n = 57)||No Adverse Events (n = 232)||p-value|
|1||15 (26.3)||61 (26.3)||0.318|
|2||7 (12.3)||42 (18.1)|
|3||19 (33.3)||52 (22.4)|
|4 or greater||16 (28.1)||77 (33.2)|
|Reported No. of cannulations|
|Fewer than 20||5 (8.8)||29 (12.5)||0.035|
|20–50||24 (42.1)||56 (24.1)|
|More than 50||27 (47.4)||136 (58.6)|
|Not reported||1 (1.8)||11 (4.7)|
|Likelihood of using US|
|In > 8 of last 10 attempts||38 (66.7)||163 (70.3)||0.549|
|In < 8 of last 10 attempts||18 (31.6)||58 (25.0)|
|Not reported||1 (1.8)||11 (4.7)|
In our multivariable analysis, history of end-stage renal disease and operators who reported intermediate experience (21–50 cannulations) were associated with an increased risk of adverse events (Table 3). No significant interactions among the variables in our final model were identified. The Hosmer-Lemeshow goodness-of-fit test resulted in a p-value of 0.87, denoting good fit. The area under the receiver operating characteristic curve was 0.66.
|Parameter||Parameter Estimate (β)||p-value||OR||95% CI|
|History of end-stage renal disease||1.26||0.002||3.54||1.59–7.89|
|< 20 vs. > 50 cannulations||0.77||0.634||0.77||0.27–2.24|
|20–50 vs. > 50 cannulations||0.81||0.013||2.26||1.19–4.32|
Several years have passed since the Agency for Healthcare Research and Quality published its report on “Making Health Care Safer” and promoted US-guided CVC.14 In that time, two ED-based clinical trials comparing US-guided internal jugular cannulation to the anatomical or landmark technique met with enormous success and approval.9,10 In both studies, success rates were over 93% and adverse events were uncommon, but the technique did not prove infallible in all patients. In this study, we identified patient factors associated with an increased risk of adverse events despite the use of US. We found that patients with a history of dialysis, and operators with an intermediate level of experience, were factors associated with adverse events during US-guided internal jugular cannulation. However, among patients with acute adverse events, none required further therapeutic interventions. Only one hematoma was noted on long-term follow-up, and we found no evidence that any interventions were required to address an adverse event that occurred during US-guided CVC.
Our findings suggest caution in patients with a history of end-stage renal disease. Many of these patients require long-term central venous hemodialysis catheters that increase the risk of stenosis and thrombosis.22–24 Furthermore, patients with strictures may lack any clinical findings such as edema or overengorgement of peripheral veins that would identify high-risk cases.12,25 When visualized with US, an engorged central vein due to a distal stricture or thrombus may give the appearance of an easy target.
Obesity, hyperinflation, and coagulopathy are commonly cited risk factors for adverse events related to CVC.14,16 In our cohort, however, these risk factors were not associated with acute adverse events. Operators may encounter more difficulty with obese or “hyperinflated” patients at other sites such as the subclavian vein. However, US guidance at the internal jugular minimizes the effect that overlying tissue or vessel depth have on successfully completing the procedure by allowing visualization of the target and needle. Operators can also avoid deep needle passes, minimizing the risk of penetration into the chest cavity. BMI alone may be a poor anatomic predictor because it may not reflect neck circumference or anatomical factors that might interfere with the approach to the internal jugular vein. Likewise, coagulopathy was not associated with adverse events. US guidance can reduce the number of needle passes and facilitate cannulation in one puncture, likely decreasing the risk of bleeding. Conversely, the relative shallowness of the vessel may allow for gentle pressure during unsuccessful attempts, decreasing the risk of further bleeding and hematoma formation. While we hesitate to suggest that US guidance would negate the effect of significant anticoagulation, its application may mitigate the risk of adverse events in patients with some degree of coagulopathy.
As prior studies suggest, compared to non–US-guided attempts, novice operators may stand to benefit most from US guidance during cannulation.10,14 In our study examining solely US-guided cannulations, operators with intermediate level skills were more likely to experience adverse events compared to novices and those with greater experience. We attribute the effect on novices to the assistance they probably received compared to those with intermediate experience, who were likely performing independently for the first time or who chose to attempt more difficult cases. Our intermediate operators likely represent physicians in a transition phase where they feel they must challenge their skill to progress from proficient operator to expert performer.
We hesitate to define “expertise” from our categories of experience because studies in the field of “expert performance” suggest that volume alone may not be sufficient to acquire high skill. Ericsson26 has demonstrated that the acquisition of expertise depends on individual and environmental factors that combine to propel individuals to acquire superior skills. Familiarity with a particular simple task threatens to arrest the development of necessary cognitive and associated skills that lead to superior performance. Unless operators actively seek improvement, simply accumulating volume may not lead to better performance.27 Operators who avoid more difficult cases may arrest their development of superior skills.
The early studies comparing US-guided to non–US-guided techniques were conducted among small groups of operators who underwent focused training or among operators with significant experience performing non–US-guided techniques. One group underwent a 2-hour didactic session and defined “experienced” when participants in that study successfully performed only 25 US-guided internal jugular cannulations.10 In another study with a success rate of 98%, the lead author performed over half of the attempts.9 The majority of operators also reported performing volumes exceeding 50 cannulations at the internal jugular site. These groups may represent subsets of physicians who sought additional training or exposure and thereby attained superior performance.
Our setting likely resembled that of institutions seeking to adopt US-guided techniques among physicians with different levels of expertise and interest in US-guided CVC. Our findings suggest that novice physicians adopting US-guided techniques without rigorous standardized training will likely experience success initially. However, they should remain cautious until they have obtained cannulation experience in several scenarios, as early success with US may not indicate the attainment of superior skills with the technology.
Further study into the area of US-guided cannulation must concentrate on validating patient and operator factors associated with acute mechanical adverse events. For example, structured US-based queries in high-risk patients might identify anatomical features that dissuade physicians from attempting cannulation or recognize cases reserved for highly experienced operators. Work with simulators may broaden our understanding of how to distinguish operator proficiency from expertise in the realm of US-guided procedures. Whether simulation exercises can develop the skills required to become an expert operator and decrease acute adverse events in the clinical arena will require future investigation.
Physicians self-reported their cannulation attempts, which might introduce measurement bias. Failed attempts may be underreported, thereby minimizing the effect of risk factors. Conversely, successful attempts in patients “perceived” as difficult may be overreported, also minimizing the identification of risk factors. However, the proportion of adverse events is similar to those seen in other observational trials both in the ED and in other settings.21,28 Blinding the outcome assessors would be difficult in this setting. However, future studies could use video-recorded attempts to ascertain specific outcomes.
Information regarding operator experience was also self-reported and only measured at one time period. While our data suggested that no single operator crossed training thresholds during the study, some operators may have logged procedures at sites outside of the ED. This might bias our results regarding operator experience toward the null. Furthermore, the number of performed procedures is not a validated measure for experience and may lead to over- or underreporting. Experience categories based on consensus opinion have identified some thresholds. It is possible that our measure may have over- or underemphasized the skills of the operators, since technical expertise will not always conform to such categories. However, our data do conform to other published US reports where performance thresholds in groups of 20–30 confer some level of proficiency.29
We chose a composite of adverse events for our study outcome, and the interpretation of our results should emphasize the composite of outcomes and not single components. We further chose to study acute mechanical complications, but did not consider central line–associated blood stream infections in our composite outcome.
Certain adverse events relied on observations that lack a true gold standard. Blinded radiologists evaluated pneumothoraces, but arterial punctures and hematomas relied on self-report or observation. Arterial punctures and cannulations tend to make themselves clinically apparent. However, there is no standard definition of a clinically relevant hematoma, and our cohort had a substantial number of these events. It is likely that this represents a degree of measurement bias given that some hematomas may have gone unreported if the study was not underway. Interestingly, in the one clinical trial that suggested fewer adverse events from US-guided cannulations, more than 50% of all adverse events were attributed to hematomas, without reporting the clinical consequences.10 Future studies should develop clinically useful definitions of what constitutes a major hematoma and what constitutes insignificant bleeding.
The statistical diagnostic evaluation of our model revealed good “goodness of fit,” but only poor to fair discrimination. Our sample, although larger than most prior studies, was relatively small. We were not able to validate our results with an independent sample. However, our model did include several frequently cited clinical parameters. The intent of our publication was descriptive, and our future efforts will concentrate on validating our results.
Ultrasound-guided cannulation of the internal jugular vein appeals to many physicians because it increases the efficiency and may decrease adverse events associated with the procedure. The procedure, however, is not infallible. We found that approximately 20% of attempts result in acute mechanical adverse events. We identified both patient (history of end-stage renal disease) and physician (intermediate experience level) factors that are associated with acute adverse events.
The authors acknowledge Max Palatnik and Shruti Patil for their contribution to this project.
- 4Percutaneous placement of central venous catheters: comparing the anatomical landmark method with the radiologically guided technique for central venous catheterization through the internal jugular vein in emergent hemodialysis patients. Acta Radiol. 2006; 47:43–7., , , et al.
- 11Development and validation of a scale for the clarity of anatomical landmarks for use in outcomes research of ultrasound guidance of central venous cannulation. Acad Emerg Med. 2006; 13:368., , .
- 14Ultrasound guidance of central vein catheterization. In: MarkowitzAJ (ed). Making Health Care Safer. San Francisco, CA: University of California at San Francisco (UCSF)-Stanford University Evidence-based Practice Center, 2001, pp 245–53..
- 26The scientific study of expert levels of performance: general implications for optimal learning and creativity. High Ability Stud. 1998; 9:75–100..
- 29Do emergency physicians gain technical proficiency for FAST, gallbladder, and deep venous scan after performing 20 scans? Acad Emerg Med. 2005; 5(Suppl 1):122., , .