October, 2007

In a perfect world, we would all be able to buy the most comprehensive health, auto, disability, life and homeowner insurance available, and be comfortable knowing that every possible loss is fully covered. In the real world, though, we all have to make tradeoffs, going without some coverages and choosing higher deductibles to obtain a reasonable cost.

Those of us who place continuous nerve blocks face a similar dilemma. Ideally, we would all use a stimulating catheter to ensure that our continuous blocks work every time. In real life, of course, it's not quite that easy.

During nerve blocks, most practitioners find the nerve plexus with a needle attached to a stimulator. When the needle nears the plexus, the relevant muscles twitch, signaling that the needle found its target. For continuous blocks, we thread a catheter through the needle's lumen and advance it beyond the needle tip. We then withdraw the needle, leaving the catheter in place. As we do, the flexible catheter tip can get dislodged, the analgesic can miss its target, and the block can fail. A stimulating catheter guards against this. It allows us to double-check catheter placement by delivering current through it. When we see the desired muscle response, we know the catheter is where it should be.

Unfortunately, it takes more time to use a stimulating catheter than a non-stimulating one, and stimulating catheters are also more costly. Because the catheter tips are flexible and challenging to direct through soft tissue, even experienced practitioners sometimes need to insert and reinsert them to achieve the desired muscle response. What's more, some studies suggest that they don't improve accuracy. However, this may be because most of these studies involve femoral nerve blocks, which don't require pinpoint accuracy. As long as we enter the iliac fossa with the needle, we can reach the target nerve; there are no structures to impede analgesic spread. This is especially true when we use large volumes of analgesic.

Some first-generation stimulating catheters also take extra time because they require us to manually detach the leads from the stimulator and attach them to the catheter. Fortunately, we are about to get help in the form of a new stimulating catheter that allows us to move the current to the catheter and back to the needle by flipping a switch.

For now, stimulating catheters remain controversial. Many of us use them only when we have extra time, or when we expect the patient will experience severe, prolonged pain if we miss the block, or if we're placing an especially difficult block. As we move forward, I hope my colleagues will be motivated to learn and use continuous peripheral nerve blocks, so all qualified patients can benefit. With additional research and more user-friendly stimulating catheter technology, we'll get even closer to this worthwhile goal.

Dr. Clark is Director of Acute Pain and Regional Anesthesia and is a Professor with the University of Louisville Department of Anesthesiology