We thank Drs. Bahk and Ryu for their interest in our article1and valuable comments. We would like to take the opportunity to address the issues raised by their insights, point by point.
First, the longest overlap length between the lower border of the clavicle and the subclavian vein (SCV) in the inner third of the clavicle was cited as one of the principal reasons for recommending a lowered shoulder position. Drs. Bahk and Ryu describe concern about cases in which a needle may cross the lower border between the midclavicular line and inner third of clavicle. However, a lowered shoulder seems to offer a more appropriate position than other shoulder positions, because overlap increases with extension to the lateral side from the inner third of the clavicle, as described in our article. The lowered shoulder also increases the proximity of the SCV to the undersurface of the clavicle. This allows reliable SCV puncture and reduces the risk of complications such as pneumothorax during the use of basic SCV puncture technique (needle advancement contacting the undersurface of the clavicle), because the needle is not advanced beyond the necessary depth. The shaded area in figure 2 of our article1extends from the SCV to the innominate vein because we were using the definition of overlap described by Land2as the area of clavicle overlapping with the SCV, including the innominate vein.
Second, although we assessed probability of contact between the needle and the SCV using the longest and shortest diameters of the vein, assessment using SCV cross-sectional area may be more suitable, as indicated by Drs. Bahk and Ryu. We therefore reevaluated contact probabilities using the products of both halves of the longest and shortest diameters and the circular constant, expressing the area of an ellipsoid, and then compared values among the three shoulder positions, because the cross-sectional area of the SCV can be regarded as an ellipsoid, as indicated in figure 2 of our article.1The result was Areadown≈ Areaneutral≈ Areaupl, being consistent with the results as assessed using SCV diameters, resulting in being substantially comparable in the contact probability among the three shoulder positions. Although we assessed overlap using the same methods described by Land2and Tan et al. 3as mentioned before, we agree with the proposal by Drs. Bahk and Ryu that overlap length of the SCV on an imaginary line drawn between the needle entry point and the midportion of the clavicular head is more relevant than using a point on the lower border of the clavicle. We are grateful to both doctors for making this recommendation.
Regarding the third and fourth comments made by Drs. Bahk and Ryu, the small number of patients participating in this clinical trial limited comparisons of SCV cannulation success rates between elevated and lowered positions only, where comparisons were expected to identify the most marked differences. From our experience, we believe that a clinical trial with a sufficient sample population will confirm the superiority of a lowered shoulder position over a neutral position in terms of success rates for SCV puncture. However, this issue must be clarified in a randomized clinical trial in the future. All catheterizations performed in the present trial were inserted into the right SCV, and no catheters were directed into the internal jugular vein. With our procedure inserting a catheter or guide wire into the SCV, advancement after a change in shoulder position from lowered to neutral may contribute to leading the catheter or guide wire toward the innominate vein. In addition, although Drs. Bahk and Ryu express concern regarding the risk of withdrawing the puncture needle from the SCV during the change in shoulder position after successful venipuncture, we believe that the risks associated with the procedure in actual practice are not as large as they suggest. Even if shoulder position changes from a lowered to a neutral or even a slightly elevated position, we have experienced minimal movement of the puncture needle. This is due to movement of the needle and syringe in an integrated manner along with the clavicle and surrounding tissue and due to the motionless area of the sternoclavicular joint, resulting in the needle remaining relatively still in the region of insertion. However, we do not recommend marked shoulder elevation. Shoulder movement after SCV puncture in infant cases may also increase the risks associated with withdrawing the needle. We think that our procedure can be applied to school-aged children and older patients, but not to children younger than school age, and infants in particular. In the case of infants, tilting the head toward the side of catheterization may help to reduce the incidence of catheter malposition into the internal jugular vein, as recommended by Drs. Bahk and Ryu.4
* Tsuruta Hospital, Ushizu, Saga, Japan. firstname.lastname@example.org