A well centered chest X ray is a must for studying the relation between central line and trachea

Abstract

We appreciate the interest shown by Lin and Tseng [1, 2] in our article. We understand the problems faced by the authors in distinguishing the placement (artery or vein) of the left sided central venous catheter (CVC). A well centered chest X ray (CXR) is the most important basic necessity while commenting on relationship of the structures in a CXR. However, we wish to draw the attention of the authors to figure 1 (CXR) provided by them. In this CXR, observe for the medial ends of the clavicles. Medial end of the left clavicle is overlapping the shadow of the vertebra while medial end of the right clavicle is far away from the vertebral shadow indicating significantly rotated CXR film. Unfortunately, this has resulted in an illusion where the trachea seems to have deviated to right side of the vertebral column while the left sided CVC appears to overlap the position of the right sided CVC. Now, we wish to draw the attention of the authors to figure 2 (CT scan). In this image, the trachea has already divided into primary bronchi and therefore, the image is taken below the level of the carina. If two vertical and parallel lines can be drawn from both edges of the sternum to meet the respective edges of the vertebra, it will become evident that the CVC in the aorta is aligned to the line joining the right borders of the sternum with vertebra while the CVC in the superior vena cava is lying outside these lines (on to the right side). This clearly demonstrates that the aortic CVC has not completely crossed over to right side even below the carina. On the contrary to this CT evidence, the CXR shows trachea deviated to right side and both CVCs appear to be on the right side of the vertebral column as well as the tracheal shadow with the aortic (left sided CVC) appearing to have crossed over to right side well above the carina (this is due to rotated film). Anatomically, carina acts as a landmark for beginning and end of the arch of aorta. Therefore, ascending aorta lies below the carina and slightly to the right side of the midline. Hence, the aortic CVC should descend down on the left side of the trachea (may partly lie within the shadow of the trachea) till carina and then the tip may cross over slightly to right side below the carina. The authors have described position of tip of the CVC as a guide to judging placement of the CVC in their article [1]. However, on the contrary, our study actually describes the course of the CVC in relation to the trachea (up to carina) and not just the tip location for detection of accidental arterial placement of the CVC [2]. Since the objective of our study was to evaluate the relationship of CVC course to trachea, we did not evaluate the course of the CVC below the carina. However, this is sufficient enough to easily distinguish CVC that is placed in aorta from venous placement [2]. Since the CT scan provided by the authors (figure 2) is taken below the level of the carina, the aortic CVC is more towards right side. More proximal sections of the CT scan or coronal plane images would have provided better understanding of the relationship between the two CVCs and the tracheobronchial tree in this article [1]. This article is the response to Chia-Wei Lin and Chun-Kai Tseng (doi:10.1007/s10877-012-9343-3).