The principal finding of this study is that placement of a PAC through the left internal jugular vein by monitoring the pressure waveform needed a longer time to cross over the tricuspid valve than the placement through the right internal jugular vein, while the time to cross over the pulmonary valve was comparable.
Anatomically, it has been well known that it may be difficult to approach from the left internal jugular vein to the superior vena cava, because the venous course forms the left internal jugular vein arcs through the innominate vein to the superior vena cava in a gentle curve, while the right internal jugular vein follows to the superior vena cava directly . This longer and more complicated route to reach the tricuspid valve from the left internal jugular vein may be related to the present results, that is, the longer time was needed to pass the tricuspid valve. The present study was designed to place a PAC by monitoring the pressure waveform, and we started the measurement after the CVP waveform was confirmed. Thus, we have to acknowledge that the CVP waveform may not always guarantee that the tip of the catheter exists in the right atrium especially in group L. So, it may be possible that the catheter migrated to a wrong vein, such as right internal jugular vein and internal thoracic vein, or made a loop in the right atrium. With helpful visual guidance including transesophageal echocardiography and X-ray fluoroscopic system, we could identify the location of the catheter and reduce the time duration in group L. In fact, recent reports recommended using transesophageal echocardiography in potentially difficult patients such as those with pulmonary hypertension [6, 7].
Thus, one may deduce that the present results showing that a longer time was needed to advance a PAC through the tricuspid valve in group L is as expected. On the other hand, it is interesting that the time duration to pass through the pulmonary valve was comparable, for it suggests that difficulty of the catheter placement to the pulmonary artery is similar regardless of the cannulation sites, once a PAC can pass through the tricuspid valve and reach the right ventricle.
It is generally accepted that visual guidance is preferred to monitoring the pressure waveform. Nevertheless, the placement of a PAC with the pressure monitoring is still common in clinical situations. Presumably, these guidance systems need additional factors, such as manpower and exposure of radiation. In addition, a recent report has documented that placement with monitoring the pressure waveform is not time-consuming compared with transesophageal echocardiographic guidance . Thus, if we try placement of a PAC through the left internal jugular vein with monitoring the pressure waveform and feel difficult to cross over the tricuspid valve, we should not hesitate to induce visual guidance to pass the tricuspid valve. On the other hand, once a PAC can pass the tricuspid valve, we may be able to advance the catheter to the pulmonary artery without difficulty.
This was designed to be a prospective and observational study in the course of 2 years, so the number of group L was exclusively small and characteristics of the patients in each group were not completely identical (Table 1). If a strict comparison of the two cannulation sites was planned, a randomized control study would be preferred. However, it is clinically established that the right internal jugular vein is the preferred site for cannulation and the left jugular vein is less reliable . Therefore, a randomized control study to compare the right and left internal jugular vein might be unacceptable from an ethical point of view. We suppose that our study design may be an alternative option, and we acknowledge that the clinical significance of the present results would be interpreted with caution.
We have to discuss potential limitations in our study. This study included multiple anesthesiologists who performed placement of a PAC, so the technique of the placement may not be identical . Thus, these individual differences might affect the results of this study.