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Department of Anesthesiology, University of Utah Orthopaedic Center, University of Utah, Salt Lake City, Utah, jeff.swenson{at}hsc.utah.edu
In Response:
We appreciate the comments of Drs. Chidiac and Perov (1) regarding our series of outpatients with continuous peripheral nerve blocks (CPNB). It is reassuring to learn that other programs have produced results similar to our own with respect to outpatient CPNB management. As more institutions adopt these protocols, patient care will be improved and the need for in-hospital pain control will be reduced.
We agree that the use of lower anesthetic concentrations during catheter infusion is beneficial. In fact, after sending more than 1,000 patients home with CPNB, we also have transitioned to the use of 0.125% bupivicaine for all outpatient catheters. This change was due in large part to reports by patients of being "too numb." We have observed that 0.125% bupivicaine provides adequate analgesia while sparing motor function in most cases.
With respect to nerve stimulation, we could not disagree more strongly with Chidiac and Perov. For many years, nerve stimulation has been the "de facto" gold standard for peripheral nerve blocks because it was the only alternative to paresthesia techniques. This is despite evidence that nerve stimulators vary greatly in their accuracy of current output (2). Much worse, motor response (even at currents of 1 mA) is not a reliable indicator of direct needle contact with the nerve (3). As for the "further refinement" of stimulating catheters mentioned by Chidiac and Perov, we would direct the readers to recent publications comparing nerve stimulating versus nonstimulating catheters (4,5). These studies do not show any benefit of stimulating over nonstimulating catheters. The largest of these studies (419 patients), concluded, "a convincing argument has yet to be made for the routine use of the stimulating catheter ..." (6).
Ultrasound has been a welcome relief for those of us who are seeking a better alternative to NS techniques. In 2005, Marhofer reported more than 4000 blocks performed using only ultrasound guidance with success rates approaching 100% (7). Since that time, his numbers have almost certainly increased. Regarding ultrasound techniques, Marhofer accurately states, "Nerves are not blocked by the needle but by the local anesthetic." Likewise, at the University of Utah, we stopped using the nerve stimulator over 2 years ago. We too, have performed over 3500 blocks (2000 catheters) using only ultrasound guidance. It should be no surprise that a technique successful for single injections would also work for catheter placement. The result has been a generation of residents from our program who have learned to "stay away from the nerve with the needle but reach the nerve with local anesthetic." A prospective study at our institution shows a success rate of 97% for single blocks and catheters placed using only ultrasound guidance (8). This same study shows the cost savings (by eliminating the cost of stimulating needles) to be more than $16,000/yr when performing more than five nerve blocks per day.
Ultrasound is ideal for catheter placement as a "stand alone" technique. We believe the nerve stimulation will soon take its place beside the copper kettle as a technique of only historical interest. In other words, yesterday’s "gold standard" has become today’s "old standard."
REFERENCES
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