RESUMEN
BACKGROUND: In this prospective, randomized study, we tested the hypothesis that interscalene catheters placed for shoulder surgery using an ultrasound needle end point provide postoperative analgesia similar in quality to those placed using a neurostimulation needle end point. Secondary end points included needle time under the skin, procedure-related pain, and the incidence of early neurological complications. METHODS: Patients presenting for shoulder surgery were recruited. Needles introduced for catheter insertion were initially guided with out-of-plane ultrasound imaging but were prospectively randomized to either sonographic placement immediately lateral to the interscalene interface (n = 41) or to an appropriate motor response at <0.5 mA (n = 40). Catheters were then advanced blindly 2-3 cm beyond needle tip. All surgery was conducted under general anesthesia. At the end of surgery, an infusion of ropivacaine 0.2% 2 mL/h with as-required hourly 5 mL boluses was instituted and continued at home for 2-5 days. Needle time under the skin and numerical rating pain score (NRPS) during insertion were recorded. Patients recorded worst NRPS, the need for supplementary ropivacaine boluses and tramadol on postoperative days 1 and 2. All patients were questioned at Day 10 for new neurological symptoms. RESULTS: There was no significant difference in the worst NRPS at rest and on movement and the requirement for supplementary ropivacaine boluses or tramadol during the first 48 postoperative hours. In one patient in group ultrasound, a satisfactory ultrasound image was unobtainable. An appropriate motor response was obtained in all subjects in group neurostimulation. The median (quartiles) needle time under the skin was 78 (65-101) s in group ultrasound and 108 (94-129) s in group neurostimulation (P < 0.001). The median (quartiles) insertion NRPS was 2 (0-4) in group ultrasound and 3 (1-5) in group neurostimulation (P < 0.048). There was no difference in the frequency of neurological complications between groups. CONCLUSIONS: Interscalene catheters placed for shoulder surgery using an ultrasound needle end point provide postoperative analgesia that is of similar quality to that obtained when using a neurostimulation needle end point. The ultrasound end point was associated with a reduction in needle under the skin time and procedure-related pain.