We appreciate the insightful comments from Drs. Maheshwari and Maheshwari on our article.1 First, we agree that marking the introducer needle might have improved the accuracy of tracking needle withdrawals in our study. However, such placement of markers on the needles is not part of most standard clinical practices and might have potentially influenced our primary outcome data by affecting subject behaviors. This study was designed to closely replicate the environment of an actual clinical procedure, using a custom-designed gel phantom model that closely simulated in vivo vessel pressures and vessel depth. Correspondingly, we used an introducer needle and a syringe procured from a standard central line placement kit. As any definition of a needle pass can be arbitrary, we chose 0.5 cm to improve objectivity. Because we defined a “pass” in this manner, our blinded assessor viewing the recorded videos counted almost every needle withdrawal as a pass. Although we did track needle passes in this manner as a secondary outcome, we emphasize the significant differences found in our primary outcome of posterior vessel wall puncture. This outcome is a surrogate of “lost” needles under ultrasound and has been used in several previous studies.2,3 In addition, the high number of carotid punctures (21% without guidance) should be highlighted as an outcome that could cause significant morbidity in an actual patient.
Drs. Maheshwari and Maheshwari also point out that there are many variations in the method of ultrasound-guided central venous cannulation.4 Even in their brief letter, they recognize that at least three techniques have been described: in-plane, out-of-plane, and medial-oblique approaches. The fact that there are so many different techniques to perform the task of vessel cannulation only reinforces that accurate needle placement using ultrasound is not always easy and no single technique is successful every time. Indeed, even ultrasound-guided in-plane approaches have been associated with a high level of procedural errors, primarily advancing without visualization.5 As with any study, we wanted to replicate the conditions of actual clinical practice, and we found that the out-of-plane needle approach was very common among our peers and numerous studies. The authors of the aforementioned letter will be pleased to know that the ultrasound technology highlighted in our article is able to track needles with any needle/probe orientation, including in-plane. However, results of our study may not be directly transferrable to in-plane approaches and confirmation with further research would be required to make any definitive statements on the benefits of needle guidance with in-plane approaches.
The authors declare no competing interests.