To the Editor:—
Correct localization of an implanted infusion pump injection port only by palpation can sometimes be cumbersome, especially in obese patients and when there are no visible signs of previous successful punctures. Fluoroscopy, if available, is sometimes used in these difficult cases. We found that ultrasound can be helpful to facilitate puncture and that the method is easily practicable.
A 43-yr-old patient with an implanted intrathecal drug delivery device (Archimedes Implantable Constant-Flow Pump; Codman, Raynham, MA) was suffering from acute breakthrough pain of malignant origin (duodenal carcinoma with lumbar bone metastases). We decided to deliver a bolus through the bolus injection port of the implanted pump. This type of pump has a separate bolus port located on the outer end of the circular symmetrical body, distant from the centrally located port to refill the reservoir chamber. Thus, depending on the orientation of the pump during the implantation, the bolus port can be found anywhere on the circumference and may be difficult to localize depending on the overlying tissue. Moreover, because aspiration through a correctly positioned bolus needle is not consistently feasible, control possibilities after positioning of the needle are limited. In our case, repeated careful palpation of the skin to find the port was inconclusive. Therefore, we decided to use sonography for localization. With a 5–10 MHz linear “hockey-stick” transducer attached to a portable ultrasound device (SonoSite 180; SonoSite, Bothell, WA) we could easily visualize the bolus port (fig. 1). The skin was marked accordingly and a needle was introduced successfully at this point perpendicular to the skin.
Only in one case report by Egerszegi et al. in 19901was ultrasound used to facilitate the repeated localization of a soft expander injection port in a pediatric patient. It is important to note that we did not perform real-time guidance of the needle under ultrasound in this case but only used sonography to mark the puncture site before disinfection and insertion of the needle. It seems to be easier for this application, is effective, and avoids sterile wrapping of the transducer.
Ultrasound guidance has gained increasing interest in regional anesthesia and pain medicine in recent years.2Many private offices and outpatient pain clinics and most hospitals are equipped with ultrasound devices today. The development of smaller, portable systems has further increased the availability of ultrasound. Compared with fluoroscopy that could also be used to facilitate port localization in difficult cases, ultrasound is portable today, more easily available, and not associated with exposure to ionizing radiation. We believe that with this easy-to-learn method, which is another useful application of ultrasound in pain medicine, multiple puncture attempts can be avoided when conventional localization of a pump injection port becomes difficult.