To the Editor:—
Klein et al. 1recently presented two cases of continuous perineural infusion of local anesthetics for the treatment of prolonged postoperative pain in an ambulatory setting. These cases deserve the following comments.
1. Patients undergoing outpatient procedures deserve the same level of care as if they had remained in the hospital. In our practice, in which continuous perineural infusions are frequently used for total joint replacements (shoulder, ankle, hip, and knee), catheters are evaluated at least once a day to verify that they provide the expected sensory block and that the site is clear and there is no leaking, inflammation, or infection. We typically prefer approaches that allow a direct visual inspection of the site. For this reason, we favor the use of a lateral approach 2rather than the posterior approach chosen by Klein et al. 1for continuous infusions at the popliteal fossa. We also insist on removing these catheters ourselves. Transferring the responsibility for the care of these catheters to the patient seems to be inappropriate. After discharge, many patients undergoing same-day surgery are home alone for extended periods of time. Because confusion is one of the early symptoms of local anesthetic toxicity, one can question whether the patient or a significant other could qualify as a proper substitute to a trained healthcare professional. Several telephone calls from a trained healthcare professional and follow-up visits represent the minimum postoperative involvement.
2. Local anesthetics are intrinsically toxic; therefore, they should always be used at the minimum effective dose. The use of a device that allows an infusion at a rate of only 10 ml/h obviously does not allow any adjustment. In contrast, there are ambulatory pumps that offer variable basal rate combined with a patient-control analgesia (Sorenson Medical, West Jordon, UT). These patient-controlled analgesia pumps allow us to use smaller rates of infusion at which local anesthetics are administered and to adapt to any additional patient needs.
3. The technique described does not allow confirmation that the catheter was properly positioned in the first patient. By injecting 30 ml ropivacaine, 0.5%, before introduction of the catheter, the authors induced motor and sensory blocks that lasted long after the patient’s discharge. The second patient was more lucky; although the pump was connected 7 h after the initial bolus injection, she remained in the hospital long enough for verification that the infusion of 0.2% ropivacaine at a rate of 10 ml/h may have produced the desired sensory block. Given the potential local anesthetic toxicity and the possible complications of the perineural infusion techniques, it is important to confirm the intensity of the sensory block before discharge. The authors may want to consider using the technique described by Ayers and Enneking, 3which is based on an initial injection of 3 to 4 ml local anesthetic solutions using the introducing needle, followed by catheter placement and injection of the remaining volume of local anesthetic through the catheter. With this technique, it is possible to verify that the catheter is well-positioned before the patient’s discharge.
4. Like the authors, we also perform popliteal blocks for patients undergoing similar surgery. Although in the past we preferred the use of the single-injection techniques, we are evaluating continuous infusions for outpatient surgery. However, independent of the technique, our protocol includes calling the patient the day of and a week after surgery to verify the absence of complications and the quality of postoperative pain control.
5. It is of special interest to recognize that the sensory sapheneous nerve blocks (without continuous infusion) were effective for 24 and 23 h, respectively. Because 0.5% ropivacaine produced a block of similar duration in the sciatic and femoral territories, is it possible that the benefits were mostly a result of the initial bolus injection? Last, after confirmation from B. Braun Medical, Inc. (Bethlehem, PA), we would like to mention that this company did not manufacture 100-mm insulated needles, but rather 89-mm insulated needles.
In our opinion, the appropriate approach for ambulatory perineural infusion should include the use of an electronic pump with patient-controlled analgesia and, most importantly, close monitoring of the patient by a trained professional.
