Stimulating catheters have been recently introduced in clinical practice. We assessed the efficacy of stimulating and nonstimulating catheter placement for pain control and local anesthetic requirements after hallux valgus repair with continuous sciatic popliteal nerve block in this comparative, randomized, blinded-to-observer study of 48 patients. A stimulating catheter was placed in groups S-125 and S-0625. The same catheter was inserted without stimulation in group NS-125. An infusion of 0.125% levobupivacaine was given in groups S-125 and NS-125, whereas 0.0625% levobupivacaine was used in group S-0625. All patients received an infusion of the test drug at a basal rate of 3 mL/h, with the possibility of an additional bolus of 3 mL every hour. Verbal analog scale (VAS) scores for pain were assessed between 6-8 h and between 19-23 h postoperatively. Multiple attempts were required for catheter insertion in all patients in groups S-125 and S-0625. Lower median (range) VAS scores for pain (0-100 points) were found in group S-125 at 6-8 h postoperatively when compared with groups S-0625 and NS-125: 5 (0-17.5) versus 60 (15-80) and 70 (25-80), respectively (P < 0.05); and lower VAS scores for pain were also found in group S-125 at 19-23 h when compared with group NS-125: 0 (0-0) and 7.5 (0-10), respectively (P < 0.05). Fewer patients required IV opioid analgesia in group S-125 than in groups S-0625 and NS-125: 0, 5, and 7 patients, respectively (P < 0.05). We conclude that efficacy in pain control was increased with stimulating catheter placement.
For sciatic nerve blockade, no study has defined the optimal volume of local anesthetic required to block the nerve. The current, prospective, randomized investigation was designed to find a minimum volume of 1.5% mepivacaine required to block the sciatic nerve using the subgluteal and posterior popliteal approaches. A total of 56 patients undergoing foot surgery were randomly assigned to receive sciatic nerve block by means of a posterior subgluteal (group subgluteal, n = 28) or a posterior popliteal (group popliteal, n = 28) approaches. All blocks were performed with the use a nerve stimulator (stimulating frequency, 2 Hz, intensity 1.5-0.5 mA) and a perineural stimulating catheter. In all patients, plantar flexion of the foot was elicited at <0.5 mA, to maintain consistency among groups. The volume of local anesthetic used in each patient was based on the modified Dixon's up-and-down method. Complete anesthesia was defined as complete loss of pinprick sensation in the sciatic nerve distribution with concomitant inability to perform plantar or dorsal flexion of the foot 20 min after injection. The mean volume of local anesthetic required to block the sciatic nerve was 12 +/- 3 mL in the subgluteal group and 20 +/- 3 mL in the popliteal group (P < 0.05). The ED95 for adequate block of the sciatic nerve was 17 mL in the subgluteal group and 30 mL in the popliteal group. The authors conclude that a larger volume of local anesthetic is necessary to block the sciatic nerve at a more distal site (popliteal approach) as compared with a more proximal level (subgluteal approach).
In this prospective, blinded study, we randomized 56 patients undergoing hallux valgus repair to receive continuous sciatic nerve block using a subgluteal (n = 28) or a posterior popliteal approach (n = 28) with a perineural stimulating catheter. Postoperatively, the stimulating catheter was connected to a patient-controlled analgesia pump with 0.0625% levobupivacaine (basal infusion rate of 3 mL/h, patient-controlled bolus dose of 3 mL, and lockout time of 20 min). Both approaches provided similar postoperative analgesia; however, local anesthetic consumption was larger in the popliteal group (4.9 +/- 1.4 mL/h) compared with the subgluteal group (3.8 +/- 1.1 mL/h; P < 0.05). We conclude continuous postoperative analgesia using stimulating catheters was effective at both injection sites; however, a subgluteal approach reduced the overall amount of local anesthetic.
In lateral sciatic nerve blockade, a more proximal approach to the sciatic nerve provides shorter onset times and more frequent success than a more distal injection site when a single injection of 20 mL of mepivacaine 1.5% is used.
Confirmation of the perivascular position of the needle by the injection of cold saline may be helpful to the perivascular technique, since the elicitation of a paresthesia indicates the correct positioning of the needle. In this prospective, randomized study of 48 patients, we found a 100% incidence of successful block with saline at 8-11 degrees C compared to 75% in a control group with saline at room temperature. The paresthesia induced by cold saline appears to be due to thermic stimulation and not to mechanical nerve compression by the saline entering the axillary space. A more frequent rate of correct positioning of the needle was found in the group with cold saline.
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