a b s t r a c t

Background: Point-of-care ultrasound guidance using a Linear probe is well established as a tool to increase safety when performing a supradiaphragmatic cannulation of the internal jugular central vein. However, little data exist on which probe is best for performing a supradiaphragmatic cannulation of the subclavian vein.

Methods: This was a prospective, observational study at a single-site emergency department, where 5 different physician sonologists evaluate individual practice preference for visualization of the subclavian vein using a supraclavicular approach with 2 different linear probes and 1 endocavitary probe.

Results: Of 155 patients enrolled, there was no clear preference any of the probes (P= .03). After pooling linear probe preference, there was a preference for either linear probe over the alternative endocavitary probe (76.8% vs 23.1%, Pb .05).

Conclusion: We observed a preference for a linear probe over an endocavitary probe. Further investigation is necessary to determine which probe is optimal for this application.

(C) 2016

Introduction

Central venous catheters are commonly placed in the internal jugular, femoral, or subclavian veins for critically ill patients who require hemodynamic monitoring or administration of centrally acting intrave- nous medications. In 2006, the American College of Emergency Physi- cians recognized and endorsed the use of point-of-care ultrasound for safe placement of these catheters to the internal jugular when a supradiaphragmatic cannulation is necessary [1]. More recently, a growing number of adult and pediatric studies have documented the potential use and advantages of point-of-care ultrasound guidance in the cannulation of the subclavian vein (SCV) as well [2-6]. Furthermore, the supraclavicular approach to point-of-care ultrasound-guided SCV cannulation has demonstrated significant advantages with success and safety when compared with the more traditional “blind” infraclavicular approach [7-13].

? Funding sources/disclosures: Dr. Fox provides consulting services for SonoSim Inc, for which he is provided stock options. No SonoSim products were used in this article. No other authors have any disclosures.

?? Ethical approval: This study was conducted in compliance with the rules and regulations

of the Health Insurance Portability and Accountability Act as well as in adherence to the Declaration of Helsinki and all other relevant federal and state laws. This study was approved by the University of California, Irvine, institutional review board.

* Corresponding author at: 333 The City Boulevard West, Suite 640, Rt 128-01, Orange, California 92868. Tel.: +1 714 456 5239; fax: +1 714 456 5390.

E-mail address: [email protected] (S. Lahham).

It is well known that various ultrasound probes can be used to aid with ultrasound-guided SCV cannulation; however, there is no agreed upon consensus as to which probe is best. On the basis of studies for the internal jugular, visualization within the supraclavicular fossa has typically been performed using a high-frequency linear probe in a longitudinal plane of the SCV, which is done to prevent transfixion of the vein and avoid the dreaded complication of an iatrogenic pneumo- thorax. Although suggested by Mallin et al [14] that the endocavitary probe may be better suited for use for supraclavicular line placement due to the cul-de-sac shape of the supraclavicular space, there remains no studies that have compared the use of different ultrasound probes to visualize the SCV from a supraclavicular approach.

In this pilot study, we sought to identify which probe is preferred by clinicians for the visualization of the SCV using a supraclavicular approach. No attempt was made to determine accuracy or easiness of performing the procedure under ultrasound guidance.

Methods

Study design

This was a single-center, prospective, observational study that compared provider preference of 3 different probes in identifying the SCV using a supraclavicular approach. The study was approved by the site institutional review board.

http://dx.doi.org/10.1016/j.ajem.2016.06.013

0735-6757/(C) 2016

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Study setting and population

The study was performed at an urban, level 1 trauma center that supports an Emergency Medicine Residency Program. The emergency department (ED) has an annual census of 57 000 patients. Adult patients presenting to the ED between February 2014 and October 2014 were eligible for participation. Inclusion criteria were age 18 years or more and ability to provide written consent in either English or Spanish. Any patient physically present in the ED was eligible for participation except for those with chest trauma or a history of chest surgery. On the basis of institutional guidelines, prisoners, pregnant patients, and those pre- senting with psychiatric complaints were also excluded from the study.

Study protocol

Five physicians of various training levels were asked to visualize the SVC using a supraclavicular approach with 3 different ultrasound probes and then indicate their preferred probe. All 5 physicians were trained in image acquisition by a fellowship trained, expert sonologist. Training sessions consisted of a 30-minute lecture and hands-on training. Under- graduate research student volunteers assisted in patient enrollment and data collection.

After obtaining consent, patients underwent bedside ultrasonography of the SCV by one of the trained physicians. A patient could be scanned by multiple sonologists, as long the sonologists were blinded to the findings and preferences of the prior scanner. A Sonosite Edge ultrasound machine (FUJIFILM SonoSite Inc, Bothell, Washington) with a long footprint linear probe (38 mm, 10-5 MHz), a short footprint linear probe (25 mm, 13-6 MHz), and a microconvex tightly curved footprint endocavitary probe (8-5 MHz) were used for image acquisition. Access to the supraclavicular fossa was obtained by placing patients in the supine po- sition with their heads rotated contralaterally. The SCV was identified by 1 of 2 methods: (1) following the internal jugular vein caudally into the supraclavicular fossa where it meets the SCV or (2) placing the probe into the fossa and angling anteriorly to capture the long-axis view of the SCV (Fig. 1). Either the right or left SCV was scanned at the discretion of the physician performing the scan.

Outcome measures

The primary end point of this study was sonologist preference by probe type for visualizing the SCV.

Statistical analysis

Sample size calculations determined that 151 images were required to detect a statistical significance of less than .05 with a power of 80%. We collected data on 174 images to allow for 10% exclusion. Study data were collected and analyzed using Research Electronic Data Capture tools. The data were analyzed used Stata (Version 12.1, StataCorp, College Station, Texas). Categorical variables were analyzed using Pearson ?² test.

Results

One hundred seventy-four patients were enrolled in the study. Nineteen (10.9%) were excluded due to incomplete data. One hundred fifty-five (90.1%) were included in the final analysis (Fig. 2). The average body mass index (BMI) was 25.9, with 49% being male. Most of the pa- tients (72.9% vs 27.1%, Pb .05) were obese (BMI, N 30.0) (Table 1). Break- down of assessments done by each sonologist were as follows: 10 by fellowship-trained sonologist (6.5%), 30 by fellow A (19.4%), 23 by fellow B (14.8%), 11 by fellow C (7.1%), and 81 by a Post graduate year-2 resident (52.3%).

There was no individual preference between each of the individual probes (38.7% [n = 60] 25 mm linear, 38.1% [n = 59] 38 mm linear, 23.2% [n = 36] endocavitary; P= .03). After pooling linear probes,

Fig. 1. The SCV from the supraclavicular view, using the L-25 (A), L-38 (B), and endocavitary probes (C).

there was a preference for linear over endocavitary (76.8% [n = 119] either linear vs 23.2% [n = 36] endocavitary; Pb .05) (Table 2). When comparing all probes, there was no difference in sonologist probe preference based on sex (P= .81) or patient BMI (P= .30).

Discussion

In recent years, a growing number of studies have documented the high rates of success and low rates of complications using ultrasound via the supraclavicular approach to assist in subclavian line placement in both pediatric and adult populations [7,8,10-12]. The largest, a retro- spective series by Bertini et al [9], reported 100% success rate in the

S. Lahham et al. / American Journal of Emergency Medicine 34 (2016) 1761-1764

Table 2

174 patients enrolled in the study

Sonographer preference by probe type

1763

Probe No. (%) P

L25 60 (38.7) .03

L38 59 (38.1)

12 patients excluded for missing sonographer preference or best image

Endocavitary 36 (23.2)

Total 155 (100.0)

situation on an obsetrical floor, for example, an ultrasound machine setup is typically only equipped with a large low-frequency curved probe and an endocavitary probe, not a linear one. A physician responding to a peri-arrest situation could use that machine to safely insert a central line (as opposed to blind).

162 patients with completed primary endpoint data

Although not evaluated, pediatric transducers with their very small, tight curved footprints and their higher frequency bandwidths, or “hockey stick”-shaped linear or cardiac curved array probes, may be preferable within the supraclavicular fossa due to their small footprint and high resolution. Better still, we believe, would be an ultrasound trans- ducer that combined the high frequency of a linear array with the curved shape of a curved-array probe. Future studies and advances in probe tech- nology are required to identify the most ideal probe for this application.

155 patients scans for analysis

7 patients excluded for missing BMI or sex

Limitations

L25 probe preferred in 60 scans

L38 probe preferred in 59 scans

Endocavitary probe preferred in 36 scans

Fig. 2. A total of 174 patients were enrolled and scanned with the 3 probes. Twelve pa- tients were excluded for missing primary end point data and 7 were excluded for missing secondary end point data.

placement of 77 subclavian and 42 brachiocephalic lines without complications. These studies offer encouragement that subclavian venous cannulation can continue to be performed safely and effectively, rather than potentially becoming the “forgotten central line” [15]. However, to date, there are no studies that identify which probe is best suited for this function. Currently, most EDs have ultrasound machines that are equipped with multiple transducers, and classically, linear probes have been used for central line placement.

We suspect much of the reason a linear probe was preferred over the endocavitary probe has to do with the size and shape of the probe. Stabilizing an endocavitary probe head within the supraclavicular fossa is technically challenging, as the sonologist must grip the wand’s handle rather than simply holding the probe and anchoring to the patient with a couple of fingers. This situation would be far from ideal in the actual setting of inserting a central line and would vary signifi- cantly from ultrasound-guided internal jugular vein and femoral central venous catheters. However, it is important to consider that in a code

Table 1

BMI distribution

BMI category No. (%) P

Underweight b18.5 4 (2.6) b.0001

Normal weight 18.5-24.9 38 (24.5)

Overweight 25.0-29.9 53 (34.2)

Obese 30.0-39.9 49 (31.6)

Very obese N 40.0 11 (7.1)

Total 155 (100.0)

There are several limitations to our study. First, only 5 physicians participated in the study, so their preference may not be generalizable to all physicians. Second, all 5 physicians were trained to place ultrasound-guided central venous catheters using linear probes, so they may have already had a natural preference for a linear probe due to previous comfort. Third, patients were enrolled in a convenience sam- ple, which may have created a selection bias. Fourth, we did not require each patient be placed in the same position during assessment, such as uniform Trendelenburg positioning with a neutral head position, which may also have limited the sonologist to best visualize the SCV, though, hopefully, this was mitigated by producing a “real- world” situation that would favor the best performing probe [16,17]. Last, from our observational study, we cannot say whether probe preference translates into improved success or Reduced complications because no data were collected on the success of vessel cannulation.

Conclusions

Physician sonologists of various training levels had a preference for a linear probe over an endocavitary probe for visualization of the SCV when using a supraclavicular approach.

Acknowledgments

We would like to thank the Emergency Medicine Research Associates Program volunteers who greatly assisted in collecting data, consenting patients and providing each patient with a study information sheet

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