How to Make Peripheral Nerve Blocks Even Safer

J. Eric Greensmith, MD, PhD, Hershey, Pa.

May, 2007

PERIPHERAL NERVE BLOCKS ARE safe; a growing body of clinical evidence confirms it. But by adding a few simple safety measures, it's possible to make them even safer. Here's how. Foremost, know the anatomy. There's no substitute for a detailed understanding of relevant structures.

Next, make every effort to help ensure accuracy. We use a blunttipped needle, and we try to block nerves where they are not encased so the nerve will move away from the needle should we get too close to it, just as an apple slips away when you're bobbing for apples. In about a third of our cases, when we feel it adds to the safety margin, we use ultrasound guidance in addition to nerve stimulation. For instance, we use it when the target nerve is close to significant vascular structures, which are highly visible on ultrasound, and to see the pleura during supraclavicular blocks to avoid pneumothorax. We also use saline rather than analgesic to perform the Raj test (a small “pre-injection”) because a local anesthetic injection might ablate the pain that would otherwise signify intraneural injection and mask the test result. To make our blocks even safer, we add epinephrine to the analgesic injection only in heavily vascularized areas, like the head and neck. We don't use it for sciatic blocks, since portions of the sciatic nerve are not well-vascularized. Eliminating vasoconstrictors (like epinephrine) helps minimize the risk of nerve ischemia.

We also take great care to minimize injection pressure. Long, thin needles and extension tubing ensure a pressure drop between the syringe and needle tip. We also inject very slowly, typically waiting 15 seconds between each 5-ml injection, so we can recognize intravascular injection early. We try to ensure that our threshold currents for nerve stimulation are not unduly low, and we stop the injection immediately if there is pain.

Finally, we keep a 20% lipid emulsion on hand in case of local anesthetic toxicity. Bupivicaine and ropivicaine cardiac toxicity are very rare, but it can be highly refractory since these amide local anesthetics are long-acting. Fortunately, both drugs are lipidsoluble, and injecting the lipid emulsion encapsulates and neutralizes the drug in the bloodstream. Several authors have published case reports showing successful resuscitation after otherwise intractable cardiac arrest.

We perform more than 4,000 peripheral nerve blocks a year. Our seizure rate is about one in 1,000, we have had no cardiac arrests, and our latest research shows that the rare case of neurologic damage is often due to factors other than the block. Our complication rate may never be zero, but by aggressively working to make a safe procedure even safer, it's possible to come tantalizingly close.

Dr. Greensmith is Associate Professor of Anesthesiology with the Penn State Milton S. Hershey Medical Center College of Medicine, Hershey, Pa.


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