◊ 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.
◊ Reviewed by W. Urmey, MD,
Dept. Anesthesiology,
Clinical Associate Professor of Anesthesiology, Weill Cornell Medical College, Associate Scientist
Hospital for Special Surgery, Dept. Anesthesiology,
New York, USA
The authors designed this study to test the hypothesis that similar postoperative analgesia could be obtained independent of whether needle tip positioning was guided by ultrasound or nerve stimulation. This study compared the analgesic effects of catheters placed in the brachial plexus at the interscalene level. An altered technique for interscalene block was employed for both ultrasonographic guidance as well as nerve stimulation guidance patients. This technique involved advancing a stimulating 18G Tuohy needle in a caudad and lateral direction into the body of the middle scalene muscle. A superficial cervical plexus block preceded catheter placement in every case. The ultrasonographic technique was out of plane and only the position of the needle tip was visualized. After an acceptable endpoint, the catheter was blindly threaded 2-3 cm beyond the needle tip in each group. The surgery itself was performed under general anesthesia. Secondary outcomes of catheter placement were compared between groups which included a new outcome defined as “needle under the skin time” as well as ropivacaine boluses for patient-controlled analgesia (PCA) and amount of tramadol consumed.
This study has multiple design flaws which significantly limit its value to the practicing clinician. One must be careful when interpreting the data presented in the manuscript and sensitive to the significance, or lack of significance, of the authors’ conclusions. The authors utilized a secondary outcome, postoperative analgesia, to evaluate accuracy of catheter positioning. A major problem, as pointed out by the authors, is the variability in postoperative analgesia associated with different types of shoulder surgery. The surgery itself was performed using general anesthesia, which included variable amounts of alfentanil. Adding further confusion to meaningful data interpretation was the fact that patient boluses of ropivacaine and another analgesic, tramadol, were used to treat pain, making it much harder to ascertain true differences between techniques. When comparing one technique to another for catheter placement, it is far preferable to measure primary outcomes such as standard sensory and motor testing by blinded observer or surgical success rate using regional anesthesia alone. It is difficult to come to any useful conclusion regarding catheter efficacy by comparing self-reported analgesia for varying procedures in the setting of other analgesics.
Regarding the respective techniques, placement of a cervical plexus block can easily result in local anesthetic flow into the brachial plexus, making it more difficult to elicit motor response to electrical nerve stimulation. Placement of “interscalene block” was not by the widely accepted interscalene block technique. Rather the needle was advanced in a caudad/lateral direction into the middle scalene muscle. This technique was used for the nerve stimulation group as well, and therefore does not represent the normal nerve stimulation guided catheter technique. Data collection during catheter insertion and surgery was not blinded. One of two meaningful outcomes reported by the authors was a 30s decrease in “needle under the skin time”. This has very little significance because set-up and initial scanning and imaging (not to mention equipment transportation) constitutes the major time consumption relating to ultrasonographic guidance for regional anesthesia. Further, for the nerve stimulation guidance group, “needle under the skin time” most certainly was affected by altering the standard technique and approach used for nerve stimulation guidance by utilizing U/S as part of the stimulation technique. Finally, by blindly advancing the catheters, the major potential benefit of U/S guidance, i.e. visualization of the catheter tip in its relation to the nerves of the plexus was never assessed.
In summary, ultrasonographic guidance may prove to be beneficial for interscalene catheter placement. However, assessment of catheter placement should be focused on primary outcomes such as visualization of the catheter tip within the plexus and whether this is associated with any differences in block quality, duration, or local anesthetic distribution by objective measurements. Small differences in time to placement, discomfort associated with the procedure, or patient-reported resulting analgesia when supplemented by other analgesics, are of questionable significance.
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