In the United States, its estimated that up to 100 million intravascular catheters are placed every year,¹ and peripheral IV access has been said to be the most common procedure performed in the E.D. ² Traditional landmark (LM) technique placement of IV catheters is usually successful. However, up to 3.2% of patients in the emergency department (ED) may require advanced placement techniques ³ (thats hard data from Pubmed, but in my practice I’m probably placing around 2-3 US-guided IV’s a shift, which is much more than 3.2% of my patients). These advanced rescue techniques include external jugular (EJ) cannulation, central venous catheters (CVC), intraosseous (IO) devices, and ultrasound-guided IV (USGIV) cannulation.  Over recent years, USGIV’s have emerged as a favored rescue technique for many clinicians.⁴

The long and short axis approach are the two generally accepted approaches for USGIV cannulation.  In the short axis technique, the provider visualizes the vein in the transverse orientation and advances the needle tip in a step-wise fashion utilizing the “sequential needle tip tracking” method.  Using this method, the provider ceases advancing the needle as soon as the needle tip is visualized by the ultrasound beam. The provider then advances the ultrasound beam proximally on the patient until the needle tip disappears, and then stops. The provider then advances the needle again until the tip appears on the ultrasound screen.  This provider repeats this sequential tracking of the needle tip in slow, 1-2 mm increments until the needle tip is seen inside the vessel lumen. Once the provider visualizes the needle tip in the vessel lumen, the provider follows the same process, tracking the needle tip inside the vessel lumen using the “vanishing target sign”.⁵

This approach, particularly the use of the vanishing target sign, is advantageous as it assures the operator that the needle tip is in the center of the lumen prior to advancing the catheter. Unfortunately, using the short axis approach, the needle tip can be lost, which may result in morbidity such as failure to cannulate the vein, arterial cannulation, nerve puncture or patient discomfort. Additionally, the provider has to estimate the correct angle of advancement of the catheter after initial venipuncture and miscalculations can lead to unintended puncture of the posterior wall or failure of successful passage of the catheter through the anterior wall.

The long axis technique requires the provider visualize both the vein and the needle in longitudinal orientation. This allows the operator to see the entire needle, including the needle tip, along the entire path into the vein without needing to adjust the probe to track the tip. This technique is also advantageous as it allows the operator to visualize the angle of cannulation, thereby allowing for appropriate angles which decrease the incidence of posterior wall puncture and inadequate anterior wall advancement. Despite these advantages, this technique requires perfect alignment of the vein, ultrasound beam and needle at all times. Movement of the probe, needle or patient by a fraction of a millimeter will disrupt the alignment of one of the three variables. This may lead to complications and increased failure rates. The majority of studies reporting superiority of the long axis over the short axis were studied under the perfect conditions of an IV access stimulator in a simulated environment and may not be reproducible in live patients.^6-8 

Equipoise exists regarding the optimal USGIV cannulation technique.  The advantage to the short axis technique is that it only requires the ultrasonographer to line up two of the three structures (vein, needle, ultrasound beam) perfectly at all times: The ultrasound beam and the needle tip.  The orientation of the needle tip and the target vessel can be modified laterally or medially as the needle tip is advanced without losing adequate visualization of the tip. If the initial puncture location is imperfect, the location of the needle tip in relation to the vein can be adjusted in real-time. The long axis technique is best at assuring the operator that the angle of advancement of the catheter is satisfactory for advancement of the catheter into the vessel.

A 2-axis technique, which combines the short and long axis techniques into a unified method may capitalize on the advantages of each technique while avoiding their respective disadvantages. In the 2-axis technique, the initial venipuncture is performed in the short axis as described above. After the vein is observed entering the vein, the vanishing target sign is performed to confirm that the needle tip is in the center of the vein. Then, the ultrasound transducer is rotated 90 degrees from the short axis into the long axis.  At this point the ultrasonographer can check to make sure that the angle of the needle will not cause the catheter to poke through the back wall of the vein. If the angle is too steep, the needle can be adjusted by flattening the catheter relative to the patient’s skin. Additionally, it is possible to confirm that the catheter itself is in the vein prior to advancing it off of the needle.

 

Here are the studies out there that allude to the 2-axis technique:

STUDY	METHODS/RESULTS	NOTES
Vogel JA, Haukoos JS, Erickson CL. Is long-axis view superior to short-axis view in ultrasound-guided central venous catheterization? Critical care medicine. 2015; 43(4):832-9. [PMID: 25517477]	Mannequin study. Residents in Denver. Concluded that long axis > short axis	”The ultrasound operator could begin with the SA approach to correctly identify the vessel which is the IJ. The ultrasound operator can then rotate the probe to the LA view to facilitate cannulation of the IJ”
Zhong X, Hamill M, et al. Dynamic multiplanar real time ultrasound guided infraclavicular subclavian vein catheterization. The American surgeon. 2015; 81(6):621-5. [PMID: 26031277]	Single surgeon did 42 subclavians using the 2 axis technique	It's called the "dynamic multiplanar real time ultrasound guided" technique
Sanchez-de-Toledo J, Villaverde I. Advanced Low-Cost Ultrasound-Guided Vascular Access Simulation: The Chicken Breast Model. Pediatric emergency care. 2017; 33(9):e43-e45. [PMID: 26599465]	Chicken breast-penrose drain vascular access model description	"With the probe in transverse position, a cross-sectional axis view was obtained for structure visualization. With the tip of the needle close to the superior wall of the vessel, a clockwise probe turn to longitudinal sectional plane was performed to identify the needle entering into the vessel"
Takeshita J, Nishiyama K, Beppu S, Sasahashi N, Shime N. Combined short- and long-axis ultrasound-guided central venous catheterization is superior to conventional techniques: A cross-over randomized controlled manikin trial. PloS one. 2017; 12(12):e0189258. [PMID: 29216331]	Mannequin study. Residents in Japan. Compared short axis vs combination short and long axis. Combo better than short axis alone	Called it the "combined short- and long-axis" technique.

Here’s an important point: When the IV is advanced with the bevel facing up, two different lines will be visualized: a superficial bevel and a deep bevel .

The more superficial line represents the area near where the catheter itself is located and should be seen advanced into the vein prior to attempting to push off the catheter from the needle.  Once these factors are evaluated, advancing the catheter off of the needle can be seen in real-time. Previous studies have referred to a similar approach but have not emphasized its importance in the successful cannulation of the veins.^8-10 

Peer review from twitter

I’ve had some great feedback from the twitter and online community.  Here are some more tips from our colleagues:

• Tim Spencer (@AirliftNurse) – When performing the short axis approach, use the word “leading” the needle tip.  You’re not “following” the needle tip with the transducer since the ultrasound beam should always be in front of the needle tip (AKA leading)
• Thomas Dolven  (@thomas1973 ) – He brought up the great point that before you try the 2-axis technique, you should make sure you feel comfortable doing the long axis and short axis first.

Conclusion:

The 2-axis technique for ultrasound-guided vascular access blends the advantages to both the short and long axes while circumventing their respective drawbacks. This technique does require being previously proficient with both the short and long axis techniques and does have a steep but short learning curve.  This technique can be performed for peripheral venous access as well as for central venous access and arterial access.

I’m planning on making a video podcast on the topic in a day or two, so be on the lookout!

Also, around 80% of what made this post legible was some peer review by Lauren Westafer (@LWestafer), Ben smith (@UltrasoundJelly) and Duane Jurma.  Thanks so much!

Here’s the Vodcast on it: