There was a recent manuscript that came across my desk from the medical journal Medical Ultrasonography. This is a peer reviewed Medline indexed journal. The publication caught my attention because it discussed using a sagittal vessel view with in-plane needle guidance (long axis) vs transverse vessel view and out-of-plane needle guidance (short axis). The article is available online in full text at Medical Ultrasonography.
This article was interesting in that they concluded that experienced users (anesthesia) had better first pass success and less carotid puncture using the short axis compared to the long axis. This seems a bit counter-intuitive. A method where the needle tip is not visualized directly was associated with better success and less complications?
There are a few things to note about this study and the methods. First short axis success was defined as aspiration of blood and visualization of “indentation of the anterior wall”. While success for the long axis was defined as visualizing the needle enter the vein. The different methods has different measures of success. The needle tip could have been as easily confirmed within the vessel lumen in the short axis as it was for the long axis rather then the surrogate marker of vessel wall deformity and blood aspiration.
Secondly the authors also state that “The operators in our study have less experience in long axis cannulation than short axis cannulation because the long axis cannulation needs more hand eye coordination and alignment of the probe than short axis approach.” I agree with this statement. The long axis is a more technically difficult method and requires more experience, skill, and attention to detail. However, if the operators were not as skilled in the long axis does this study really evaluate long vs short or merely the operator’s skill with each technique?
There was also no mention of frequency of posterior or deep wall punctures and possible resultant hematomas. There were 2 carotid punctures (non-significant) in the long axis group, but not a clear discussion of the reasons leading up to accidental punctures. Was that a failure of the technique or operator error?
In the end this article is interesting but does not answer the question of long vs short axis for me. The limitations of the study make drawing practice changing conclusions difficult. I personally prefer the long axis technique to visualize the needle and its movement during realtime with relation to the vessel and the posterior wall.
In the end it shows that ultrasound is a tool and technique and experience is important, or as Masharu Morimoto once said (world renowned chef), “my knife is sharp, but my arm is sharper”. Referencing that his knives are important but his skill and technique is more important.
I completely agree with you. What good is this study if they admit that they have less experience with the long axis? A direct comparison cannot be made in this case.
Perhaps the part that is most disturbing, is the emphasis that both arterial punctures were in the long axis group. This can only happen for two reasons in the long axis: either they were not visualizing the needle on the screen at the time of puncture, or they were visualizing the needle enter the artery (i.e. they were looking at the wrong vessel). Because, as you state, success in the long access was defined as visualizing the needle enter the vein, one must assume that they made the second error — visualizing the artery at time of puncture. Not being able to identify artery vs. vein speaks more to their comfort with the technique than it does the technique itself.