In this study, we retrospectively analysed the post-operative chest radiographs of infants who underwent cardiac surgery and assessed the possibility of using a vertebral body as a radiographic landmark for the identification of the depth of right internal jugular vein catheterisation. CVC insertion, including internal jugular vein catheterisation, femoral vein catheterisation, and subclavian catheterisation, is a very important perioperative technique. Currently, the most widely utilised form is right internal jugular vein catheterisation.12 The optimal timing of surgical treatment for children with certain congenital heart diseases is during infancy. Infants have a relatively large head and short neck; therefore, it is difficult to insert and place the right internal jugular vein catheter, especially in terms of the appropriate depth. There have been reports that improper CVC placement can cause serious complications in infants.13–15
According to current literature, the carina can be used as a reliable reference index for the depth of right internal jugular vein puncture. In this study, we retrospectively analysed post-operative chest radiographs of infants and observed that the carina was not clearly visible in a substantial proportion (36%) of chest radiographs; however, the vertebral bodies were clear in 100% of cases. Moreover, we discovered that the fourth thoracic vertebra was at the same level as the carina in most cases (98%), contrary to what is observed in adults11; this discrepancy may be due to differences in the physical development stages of infants and adults. Our results suggest that the fourth thoracic vertebra can also be used as a radiographic marker for optimal CVC positioning, which may reduce complications.
Previous studies on the depth of right internal jugular vein catheterisation in infants, e.g. that of Lopéz Álvarez et al.,16 have relied on special equipment for guidance, such as those used during transoesophageal echocardiography and ultrasonography; these are expensive, difficult to operate, and not suitable for most hospitals. Other researchers, such as Uchida et al.,17 have relied on chest radiography to locate the carina for the optimal placement depth of the CVC. As discussed above, this is not possible in all cases; we could only distinguish the general anatomy of the trachea, as well as that of the left and right main bronchi; only the approximate position of the carina was determined.
The distance from the fourth thoracic vertebra to the CVC tip in our study was 11 ± 8 mm; in 77% of cases, the tip was below the fourth thoracic vertebra. In a previous study, it was revealed that the junction of the superior vena cava and the right atrium may be 22 mm below the carina in infants.9 We therefore speculated that the CVC may be too deep when placed more than 22 mm below the fourth thoracic vertebra, as this may cause the CVC to enter the right atrium. In this study, there were seven cases where the CVC tip was located more than 22 mm below the fourth thoracic vertebra; in one case, the distance from the CVC tip to fourth thoracic vertebra was 40 mm. Theoretically, the CVC may enter the right atrium when placed at such a depth; however, such a complication was not recorded by the surgeons. In 66 cases, the catheter tip was located no more than 22 mm below the fourth thoracic vertebra; we speculate that the CVC tip is located in the lower segment of the superior vena cava when placed at this depth, which is reported as the most suitable depth.18,19 However, it has been reported20 that head position may have an effect on the internal jugular vein size and, thus, the catheter tip position. If placed near the fourth thoracic vertebra or carina, this effect is likely minimal; however, if the CVC is placed closer to the right atrium, a change in head position may cause the catheter to enter the right atrium, interfering with the operation and risking complications such as cardiac perforation and tamponade. Since we did not require the same head position during data collection, a closer proximity of the catheter tip to the right atrium increases the risk of complications. Based on the above analysis, the CVC should be withdrawn approximately 10 mm, on average, to the level of the fourth thoracic vertebra; this seems to be a reliable indication of a safe CVC depth for the children analysed in this study. According to our observations, the CVC tip was located above the fourth thoracic vertebra in a safe position in three cases. However, a position that is too high would lead to inaccurate determination of the central venous pressure, increasing the risk of the catheter being pulled out.
This was a retrospective study, which resulted in certain limitations. First, post-operative chest radiography was not performed using standardised radiographic parameters for observing the position of the carina; therefore, not all carina were visible. However, regardless of the radiation parameters, vertebral bodies were clearly visible. Second, during chest radiography, the infants’ head positions were not uniformly fixed, which may have affected the depth of CVC placement. Third, many studies have indicated that the insertion depth of the catheter was highly correlated with infant height6,7,21; however, we did not obtain infant height data from the medical records, and were therefore unable to determine whether there was such a correlation. Fourth, we did not receive feedback from the surgeon regarding the position of the catheter during the operation; therefore, we could not verify our results with more clinical information. Finally, we only focussed on infants; our results are therefore not necessarily applicable to children of all ages. These limitations highlight the need and scope for further, preferably prospective, studies on this topic.