A nerve block is an injection of local anesthetic close to a nerve. The drug attaches to the nerve and blocks any nerve signals travelling to or from the brain. The blockage occurs where the needle is inserted. Depending on the kind of nerve being blocked, the patient may feel numbness (no nerve signals going to the brain), weakness/paralysis (no nerve signals coming from the brain) or both.
Anyone who has had “freezing” for dental work has had a nerve block and knows what it can do. Spinals, epidurals and caudals are nerve blocks that affect the spinal cord and/or nerves. If enough local anesthetic is injected, everything below the level of the injection can be “frozen” to the point of allowing surgery.
The safety of nerve blocks depends on the skill of the person performing them, the health of the patient and the location of the injection. Some nerve blocks are relatively simple and safe, requiring less training and few special precautions. Examples include various blocks in the head, face and limbs. Others require a higher level of technical skill and are inherently more dangerous when the target nerve is near organs, blood vessels or other nerves that could be damaged. Some blocks can only be performed using imaging technology to see exactly where the needle goes. Diagnostic facet nerve and celiac plexus blocks are examples.
Certain nerve blocks in the head, neck and back are often used repetitively in the management of chronic pain. I have used them to treat headaches, neck/trapezius pain and back pain. Some patients get relief that lasts only about as long as the “freezing” does, i.e. as long as the local anesthetic does. Depending on the kind and amount of the drug injected this is usually no longer than a few hours. However some people get relief that lasts longer – days or weeks – for reasons that are not scientifically clear.
There has been little good research on the use of nerve blocks for chronic pain. There is some evidence to support the use of blocks in the management of some headaches but we are far from understanding what kind of patient with what kind of pain might benefit from what kind of nerve block. This is a problem for pain patients when offered this kind of treatment because they have little evidence to rely on when making a decision.
Fortunately most of the nerve blocks now being offered for headache and other common forms of chronic pain are relatively safe and technically simple. Nevertheless, it is crucial that a patient be evaluated carefully and fully informed of potential risks before undergoing treatment. Furthermore, the doctor must also have the skills, additional personnel and equipment immediately at hand to deal with any possible complication that might arise.
Over the years I’ve performed hundreds of nerve blocks on hundreds of patients. None were cured, some achieved good relief for weeks or months and some had little response after the local wore off. I have seen very few serious complications and none of my patients have sustained a permanent injury. The results, to me, seem like any other treatment I’ve used for treating chronic pain. Some people do okay and others not so much. I see nerve blocks as a potential tool that desperately needs more testing if we are going to use it rationally.